;ODERN ELECTIffCAL'^ [«]3SI!llLilIll HOESTMANN &" WUSIM ^ j*^^ g M ^ML_ .!w^i k^'AQr m ])^7 Class. Book. N». COPM^IGHT DEPOSIT. m. MODERN Electrical Construction A RELIABLE, PRACTICAL GUIDE FOR THE BEGINNER IN ELECTRICAL CONSTRUCTION SHOWING THE LATEST APPROVED METHODS OF INSTALLING WORK OF ALL KINDS AC- CORDING TO THE^SAFETY RULES OF THE National Board of Fire Underwriters By HENRY C. HORSTMANN and VICTOR H. TOUSLEY Authors of "Modern Wirhig Diagrams and Descriiitions" "Electf-ical Wiring and Construction Tables, Etc." 3IUuBtratf& Second Edition ■ — Revised and Enlarged CHICAGO FREDERICK J. DRAKE & CO., PUBLISHERS ftfH^.stY o1 GONfiRE'SS? I wo oooies rtetwvcc OLAttS. 3- AAC Nw. COPY a. ^ Copyright, 1904 BY horstmann and tousley Copyright, 1908 BY HORSTMANN AND ToUSLEY ^ \ PREFACE In this volume an attempt is made to provide the beginner in electrical construction work with a reliable, practical guide; one that is to tell him exactly how to install his work in ac- cordance with the latest approved methods. It is also intended to give such an elaboration of "safety rules" as shall make the book valuable to the finished work- man as well. To this end the rules of the "National Electrical Code" of the National Board of Fire Underwriters have been given in full, and used as a text in connection with which there is interspersed in the proper places a complete explana- tion of such work as the rules may apply to. This method of teaching and explaining practical electricity may at first glance seem somewhat haphazard, but it resembles very closely the actual method by which the most successful, practical work- men have learned the trade. It is thought that explanations pertaining directly to the work in hand will be more deeply considered and more likely to be fully comprehended than explanations necessarily more abstract. It should be noted that, while the rules published in the "National Electrical Code" are standard and work done in conformity with them will be first-class, several of the larger cities have ordinances governing electrical work which con- flict in some details with these rules. Workers in such cities should, therefore, provide themselves with copies of these ordinances (usually obtainable without charge), and compare them with the rules given in this work. It is necessary for the electrical worker at all times to keep himself posted, for safety rules are liable to change. The tables concerning screws, nails, number of wires that can be used in conduit, etc., are especially prepared for this volume, and give to it particular value for practical men. The Authors. PREFACE TO SECOND EDITION The favorable reception which the first edition of this work has received at the hands of electrical workers generally has induced the authors to prepare this, the Second Edition. Considerable new matter, notably a section on Theater Wir- ing, has been added. All the necessary alterations and addi- tions have been made in the text to conform to the latest issue of the National Code, together with the required explan- ations and illustrations. Other sections have been extended and the whole work has been carefully gone over and re- vised wherever the progress of the art has made it desir- able. The Authors. CHAPTER I. The Electric Current. It is quite customary and convenient to speak of that agency by which electrical phenomena, such as heat, light, magnetism, and chemical action are produced as the electric current. In many ways this current is quite analogous to cur- rents of air or water. Just as water tends to flow from a higher to a lower level, and air from a region of greater density or pressure to one of lesser density, .so do currents of electricity flow from a region of high pressure to one of low pressure. Currents of electricity form no exception whatever to the general law of all action, which is along the lines of least resistance. It must not be understood, however, that electricity actually flows in or along a conductor, as water does in a pipe, and the analogy must not be carried too far, for the flow of water in pipes is influenced by many conditions which do not influence a flow of electricity at all, and vice versa; there are conditions surrounding conductors, which influence the flow of electricity which do not affect the flow of water. Above all, let it be understpod that electricity is not inde- pendent energy, any more than the belt which gives motion to a pulley is. In other words, it is not a prime mover, it is simply a medium which may be, used for the transmission of energy, just as the belt is used. To use electricity as a medium for the transmission of energy, it must be, we may say, compressed, or, to use a more properly technical expres- sion, a difference of potential or pressure must be created in a system of conductors. This is very similar to the use of air 8 MODERN ELECTRICAL CONSTRUCTION. for power transmission ; this must also be compressed so that a difference of pressure exists within a system of piping. It is the flow of electricity or air which takes place when switches or valves are operated and which tends to equalize this pressure, i. e., flow from high to low pressure, that does our work. The real energy, however, (so far as we are con- cerned), to which we must look for our initial motion in either case is derived from the coal which generates steam ; or, in the case of water-driven machinery, the rays of the sun which evaporate water, allowing it to be carried to higher levels, from whence it flows downward over dams ar.d falls on its way back to the lowest level. In the battery, the real energy is that of chemical action, which is transformed into electrical energy. The flow of current can take place only in a systen?. of conductors which usually, for convenience, are made in the form of wires. The current for practical purposes may be considered as flowing along such wires only. It is not, how- Figure 1 ever, necessary that these wires should be of any particular size, or consist all of the same material. In an electric bat- tery, part of the circuit consists of the liquid contained within the battery ; the rest being made up usually of wire. In an incandescent light circuit part of the circuit consists of the ELECTRIC CURRENT. 9 lamp filament (usually carbon), while the balance of the cir- cuit consists of copper wire. The flow of current is also said to have a certain direction ; that is, it is noticed that many of its effects are reversed when the terminals of the battery are reversed. Referring to Fig. 1, which shows a battery of three cells, the current flows from the copper element at bottom of jar 1, along the wire to the zinc element at top of jar 2, thence through the liquid to the copper element at bottom of jar 2, and from there to the zinc at top of jar 3, etc., and finally through the wire a back to the starting point. Within the battery the current flows from the zinc to the copper and the decomposition of the zinc gen- erates the current. In the wire outside of the battery the cur- rent flows from the copper to the zinc as indicated by arrows. The combination of battery and wire is known as an electric circuit. The current will flow in this circuit only while it is complete, that is while each wire connects to its proper place as shown. If any wire is disconnected, the current flow will cease. Such a circuit is said to be open, but when all connections are properly made it is said to be closed. Work can be obtained from a flow of current in many ways. If the current be forced to flow over a wire which is very small in proportion to the current carried, it will be heated thereby and finally melted if the current is excessive. This is how electric light is obtained. If a wire carrying current be w^ound many times about an iron bar this bar becomes a magnet; that is, while the cur- rent is flowing around it, the bar has the power to attract other objects of iron or steel. The bar if made of well an- nealed iron will be a magnet while current is flowing around it, but will cease to be magnetic whenever the current flow ceases. Upon this fact the operation of electric bells, telegraT)h instruments and motors is based. If a current of electricity flow through a properly arranged 10 MODERN ELECTRICAL CONSTRUCTION. "bath," one of the plates will be gradually consumed and the other increased in weight. This effect is made use of in electro-plating, etc. If the jar contains water slightly acid- ulated and the current flows through it, the water will be decomposed and oxygen and hydrogen gas will be formed. This and many kindred effects are daily used in thousands of chemical laboratories. If a wire carrying an electric current be placed very close to another wire forming a closed circuit, a wave of current will be induced in that wire every time the current in the other is made or broken, i. e., whenever it starts to flow or stops flowing. This fact forms the basis of the alternating current transformer. All of these facts are used sometimes together, sometimes singly in measuring the electric current. Conductors and Insulators. Electrically speaking, all substances are divided into two classes. They are either conductors or insulators. By thi'-^ is not meant that some substances can carry no current at all, for, as a matter of fact, there is no such thing as either a perfect conductor or a pecfect insulator. A current of elec- tricity can be forced through any substance, provided the pres- sure (E. M. F.) be made great enough, and there is no easier path open to the current. The two terms, conductor and insulator, are relative terms and must be understood simply to mean that the electrical resistance of a good conductor is infinitesimally small as compared to that of a good insulator. The lower the specific resistance of any substance, the better its conducting qualities ; the higher the specific resistance of any substance, the better will be its insulating qualities. At the left is given a list of good conductors, in the order qf their conductivity, the figures representing the relative con- ELECTRO- MOTIVE-FORCE. 11 diictivity of these metals. A list of insulators is given at the right; all of these are more or less affected by moisture, los- ing their insulating qualities vv^hen wet. Silver 100.0 Dry air. Fiber. Copper 94.0 Rubber. Wood. Gold 73.0 Paraffin. Shellac. Platinum 16.6 Slate. Iron 15.5 Marble. Tin 11.4 Glass. Lead 7.6 Porcelain. Bismuth 1.1 Mica. Pressure or Electro-Motive Force. Currents of electricity flov^ only in obedience to electrical pressure. This pressure is measured and expressed in volts, the unit of electrical pressure being the volt. If we speak of water or steam pressure, we speak of it in pounds, the pound being the unit of measurement. In speaking of elec- trical pressure we refer to it as of so many volts. There is no direct connection between the pound and the volt, but each in its place means about the same thing. The volt is defined as that difference of potential (pres- sure) that must be maintained to force a current of one ampere through a resistance of one ohm. If we have a resistance greater than one ohm and wish to send a current of one ampere through it, we can do so by increasing the pressure or voltage, as it is termed, accordingly. The current flowing in a circuit can also be reduced by reduc- ing the voltage. The ordinary incandescent lamps operate at about 110 volts pressure, although some are built for 220 volts. An elec- tric bell requires about 2>4 volts (a battery of 2 cells) for proper operation. 12 MODERN ELECTRICAL CONSTRUCTION. Resistance. We have seen that a flow of current always takes place along or in a conductor. Every conductor, no matter how large or small it may be, offers some resistance to this flow of current just as the water pipe offers more or less resisiance to the flow of water. This resistance may be measured and expressed in ohms; the unit of electrical resistance being the ohm. The ohm is defined as that resistance which requires a difference of potential of one volt to send a current of one ampere through it. If we should desire to send a greater cur- rent through any resistance, we can do so by increasing the pressure, just as we can increase the flow of water in a pipe by increasing the pressure or head of water in the tank that supplies it. If the pressure is fixed we can decrease the current by using a wire of greater resistance or increase it by using wires of lesser resistance. The ohm is the resistance of a column of mercury 106.2 centimeters long (about 3^ feet) and one square millimetre (about .0015 sq. in.), in cross-section, at the temperature of melting ice. The resistance of a No. 14 copper wire about 380 feet long is equal to one ohm. The resistance of all conductors increases directly as the 3' Figure 2 length and decreases as the cross-section increases. In Figure 2 the resistance of the two bars of copper is exactly equal. Bar No. 1 having a cross-section of 4 square inches and being 4 feet long, while bar No. 2 has a cross-section of only 1 square inch and is only one foot long. If bar No. 1 were OHMS LAW. 13 reduced to a cross-section of 1 square inch, it would become 16 feet long and would have a resistance 16 times as great as that of bar No. 2. Current. The electric current is the result of electrical pressure (volts) acting through a resistance, and is measured in amperes, the ampere being the unit of current strength. The ampere is defined as that current which will flow through a resistance of one ohm when a difference of potential or pres- sure of one volt is maintained at its terminals. The ampere expresses only the rate of flow, not the quan- tity. Knowing the amperes if we would know the quantity, we must multiply by the time that the rate of flow continues. Ihe rate of flow is analogous to the speed of a train; unless we know how long the train is to maintain a certain speed, we have no idea how far it is going. Quantity in electricity is measured in coulombs. The coulomb is the quantity of current delivered by a flow of one ampere in one second. Ohm's Law. Ohm's law expresses the relation of the three principal electrical units to each other and forms the basis of all elec- trical calculations. This law states that in any electric circuit (with direct current) the current equals the electro-motive force divided by the resistance. The current, we have already seen, is the medium which does our work. Current flow, we see from this law, can be increased either by increasing the electro-motive force, or electric pressure, which causes the flow; or by decreasing the resistance which tends to prevent current flow. Expressed in symbols it is this: I=E/R; where I stands for 14 MODERN ELECTRICAL CONSTRUCTION. current, E, for electro-motive force, and R for resistance. If, as an example, we have an electro-motive force (which we shall henceforth designate by the customary abbreviation, E. M. F.) of 110 volts and a resistance of 220 ohms, the resulting current will be 110 divided by 220=^ ampere, being approxi- mately the current used in a 16 cp. incandescent lamp at 110 volts. Thus it will be seen that by a very simple calculation we can find the current flow in any conductor if we but know the E. M. F. and the resistance of that circuit. This formula can also be used to find the E. M. P., if we know the value of current and the resistance, since E divided by R=I ; I times R must equal E. If the current and resist- ance are known, we need only to multiply them together to find the E. M. F.; IXR=E. Knowing the current and E. M. F., we can find the value of the resistance by dividing the E. M. F. by the current; E/I=R. As a practical application of these formulas: If we wish to know how much current a certain E. M. F. can force through a certain resistance, we must divide the E. M. F. (volts) by the resistance (ohms.) If we wish to know what E. M. F. (volts) will be necessary to force a certain cur- rent (amperes) through a certain resistance, we need only multiply the current (amperes) to be obtained by the resist- ance in ohms. If we wish to know how much resistance (ohms) must be placed in a circuit to keep down the current flow to a certain limit, we need only divide the E. M. F. (volts) by the desired current (amperes) ; the result will be the value in ohms of the required resistance. Power. The power consumed or transmitted in an electric cir- cuit equals the product of the volts and amperes ; pressure and current. POWER. 15 To find the power of a steam engine, we must know the pressure of the steam and the quantity used ; the power con- tained in the water of a dam depends upon its vokime and its head. The power we can obtain from the wind depends upon its speed and the surface we expose to it which also measures the quantity. All of these cases are analogous and similar. Power ex- presses the rate of doing work, thus the rate of work is the same whether we are lifting one pound at the rate of 100 feet per minute, or 100 pounds at the rate of one foot per minute. The unit of electrical power is the watt. It is the power expended in an electric circuit when one ampere flows through a resistance of one ohm, or when a difference of potential of one volt is maintained in a circuit having a resist- ance of one ohm. In an electric light circuit, for instance, as far as the power is concerned, it is immaterial whether each lamp requires 110 volts and ]4 ampere, or 55 volts and one ampere, or 220 volts and % ampere. The power (watts) expended in an electric circuit is always equal to the volts multiplied by the amperes; thus, one ampere at 1,000 volts is equal to 100 amperes at 10 volts, or to 200 amperes at 5 volts. In any power transmission whenever the pressure (volts) is lowered, the current (amperes) must be increased or the power (watts) will fall off, and, on the other hand, whenever the pressure is increased the current may be decreased. Instead of multiplying volts by amperes, we can find the power in an electric light circuit by multiplying the current by itself and then by the resistance; or the E. M, F. by itself and divide by the resistance. Thus knowing the volts and the amperes, we use the formula E X I=W. Knowing only the amperes and the ohms, we may use the formula, V X R = W ; and lastly. 16 MODERN ELECTRICAL CONSTRUCTION. knowing only the volts and ohms, we use the formula, EVR = W. In the above E stands for E. M. P., or volts ; I for current or amperes ; and R for resistance or ohms. Divided Circuits. Currents of electricity always flow along the paths of least resistance just as currents of water do. Water, it is well known, will not flow over the top of a mill dam while Figure 3 there is an opening alongside of it through which it can flow. If a barrel of water be provided with two openings, one large opening and one small, a much larger quantity will flow out through the large opening than through the small. This is because the resistance to the flow of water of the large opening is so much less than the resistance of the small opening. An electric current will act in just the same way; the conductor having the lesser resistance will carry the greater current. If we know the resistances of the different paths open to a certain current we can determine to a nicety how much current will flow in each. In Figure 3, which repre- sents diagramatically a battery of two cells and an electric circuit, the resistance of the two paths, a and b, is equal to DIVIDED CIRCUITS. 17 10 ohms each, and the current will divide equally between them. If the resistance of a were 5 ohms, and that of b, 10 ohms, two-thirds of the total current would pass through a and the one-third through h. In all such divided circuits, the current is always in- versely proportional to the resistance and the simplest way to find the current in each is to add the resistances of the two circuits ; for instance as above, 5 plus 10 equals 15 ; now 5/15 of this current will flow through the 10 ohms and 10/15 of the current will flow through the 5 ohms. To determine the combined resistance of the two wires, a and h, we need simply to consider them as made into one wire. If they are both alike, they would, if made into one wire, be twice as large as either one is at present, and would then have only one-half as much resistance as either one had before; for the resistance of any conductor increases directly as its length, and decreases as the cross-section increases. The combined resistances of any two conductors can be found by multiplying their two resistances together and dividing this product by their sum. Thus, again taking the value of a and h as 10 ohms each, 10X10 equals 100, this divided by 10 plus 10 equals 5, which is the combined resistance of the two. If we have a large number of branch circuits as shown in Figure 4, which represents diagramatically an incandescent hhh:^ Figure 4 electric light circuit of 12 lights (which is equal to 12 separate circuits, since each lamp really forms a circuit by itself), we can find the joint resistance of the 12 by proceeding as before; that is, multiplying together the resistance of the first and 18 MODERN ELECTRICAL CONSTRUCTION. second lamp and dividing by the sum of these resistances ; next take the result so obtained (which is the combined resist- ance of the first two lamps) and with it multiply the resist- ance of the third lamp and divide by the sum as before. By repeating this operation and always treating the joint resist- ances already found as one circuit, the joint resistance of any number of such circuits can be found. Another and a very much quicker way consists in using the following formula : The joint resistance of any number of parallel circuits is equal to the reciprocal of the sum of the reciprocals. The reciprocal of any number is 1 divided by that number. If we have three circuits, having respectively 10, 20, and 30 ohms resistance, we proceed in the following way : The reciprocal of 10 is 1/10, of 20, 1/20, etc., the joint resistance, there- fore, is 1/10 plus 1/20 plus 1/30 equals 11/60, and 1 divided by this number which is 5 5/11. These methods are only necessary when the resistances are of different values. When all of them are alike, as is usual with incandescent lights, the resistance of one lamp needs only to be divided by the number of lamps to find the joint resistance. Thus, supposing each of the 12 lamps to nave a resistance of 220 ohms, the joint resistance of the circuit would be 220/12 = 181/3. CHAPTER II. Electric Bells. We are now in a position to apply the electrical laws we have just discussed practically, and for this purpose may take up electric bells and bell circuits. Figure 5 shows an electric bell, push button and battery, all connected up and complete. The action of the bell when Figure 5 fully connected is as follows : Pressing the push button closes the circuit and current at once flows from the carbon pole marked + through the push button to the binding post A on the bell frame, thence along the fine wire W to the iron frame-work supporting the armature, B. This frame- 20 MODERN ELECTRICAL CONSTRUCTION. work is in electrical connection with B. The armature, B, is provided with contact spring S, which normally rests against the adjusting screw, C. The current now passes from the contact spring to the adjusting screw and from it to the wire wound on the magnets, M, around the many turns of wire to the binding post, D, and back to the zinc pole of the battery marked — . The current circulating many times in the wire wound on the spools of M makes the iron cores magnetic so that they now attract the armature B. When this armature is at- tracted, it moves towards the magnets, M, and carries the small contact spring with it, thus breaking the connection be- tween C and S. This stops the current flow and the magnets, M, are at once demagnetized, thus releasing the armature B, which flies back and again clones the circuit at CS, this causes the armature to be attracted again and once more the circuit is broken. In this way the armature is made to strike the gong continuously while the circuit is kept closed at the push button. When the button is released, the circuit is permanently open and the bell at rest. In the figure there is shown only one cell, this, if a good form is selected, is sufficient for a new bell if the circuit is not long. When, however, the bell is used much the contact points are eaten away by the little sparks occurring every time the bell breaks the circuit. Dirt is also likely to gather on them and prevent good contact being made. Both of these factors add resistance to the circuit, and consequently lessen the current flow. We have seen before that the current equals the E. M. F. divided by the resistance, and in order to obtain the necessary current flow to operate the bell, we may either clean the contact points to lessen the resistance, or increase the E. M. F. by adding another cell in series with the first. ELECTRIC BELLS. 21 The latter expedient is by far the better, because it gives us a little surplus of power which is very useful to over- come variations in adjustment of the contact spring, loose contacts, dirt, etc. We should avoid using too many cells as well as not enough. If too many cells are used, there Q D n Q n •t ji) Figure 6 will be much unnecessary damage done to contact points by the larger sparks. If the circuit is very long, the great length of wire will also provide additional resistance. This can be overcome in two ways, by increasing the E. M. F. as above, or by using larger wires. We have already seen that the larger the wire, the less will be its resistance. It is common practice to use 22 MODERN ELECTRICAL CONSTRUCTION. No. 18 copper wire for all ordinary distances and for single bells. With large bell systems, it is customary to use No. 16 or 14 for the main wire, which leads to all of the bells and may be called upon to supply several bells at the same time. Figure 6 shows a diagram of such a system and in case the three push buttons are used at the same time, three times as much current will flow in the main or battery wire a as in either of the other wires. We have seen before that currents of electricity divide among different circuits in the inverse ratio of their resist- ances. In other words, the circuit having the least resistance will carry the most current. If our bell system, Figure 6, be "grounded" at the two points x and y (i. e., bare wire in contact with metal parts of buildings which are connected together) the current instead of flowing through the longer circuit and the bell, will flow through the short circuit and leave it impossible to operate the bells. If the contacts, at X and y are poor, i. e., of high resistance, only a small part of the current will leak from one to the other. In such a case, the bells may work properly, but the battery will soon run down and there is a strong likelihood that one of the wires will be eaten away through electrolytic action. To prevent troubles of this kind, bell wires should be well in- sulated and kept away from pipes or metal parts of building. Damp places should also be avoided and special care is recommended for the battery wire a, Figure 6. For further information concerning diagrams, etc., of bell circuits the reader is referred to Wiring Diagrams and Descriptions by the authors of this work, Fred J. Drake & Co., Chicago. Bell wires are usually run along base boards, over picture mouldings, etc., in some cases they are also fished as explained further on. Batteries should be located in cool,' dry places, where they are not liable to freeze, and where they are readily accessible as they must be kept nearly full of water and must be recharged from time to time. 23 The Telephone. The principle and action of the Bell telephone can be best explained by reference to Figure 7. In this figure, A repre- sents the transmitter, and B, the receiver. The essential parts of the transmitter are : the diaphragm, a; an electric "circuit, containing a battery, bj and consisting of the wires, c, c^ and partly wound upon an iron core, d. This electric circuit, it will be seen from the figure, con- nects with one pole to the diaphragm, a, and with the other to a small metal plate, \ / Figure 14 ished. This is accomplished by means of an automatic regulator connected to the dynamo. The current used with this system seldom exceeds ten amperes and large wires are never required. This system is best suited for street lighting where long distances are to be covered. In these diagrams, D represents the dynamo, and F, the "field" coils of the dynamo. With constant current systems the "fields" are usually in series with the armature of the dynamo, as shown in Fig. 14, and the lamps, so that the same current must pass through all. With ccnstant WIRING SYSTEMS. 33 potential systems, the field coils are generally independent of the rest of the circuit. With such systems the current used in the circuit is so variable that it cannot be used in the fields. Another system, known as the multiple arc or parallel system, is shown in Figure 15. In this system the E. M. F. never varies, but the current is always proportional to the Figure 15 number of lights used. If, for instance, only one light is used, there is a current of about one-half arhpere, but if ten 16 cp. lights are used there must be a current of about five amperes. Where many lights are used with this system, the main wires require to be quite large, and must always be proportional to the number of lights. This system is oper- ated usually at 110 volts and is suitable for residences, stores, factories and all indoor illumination. It is not well adapted to the transmission of light and power over long distances. The 3-wire system shown in Figure 16 combines many of A i i i i A A H t t t t t t Figure 16 the advantages of both the foregoing systems. As will be seen from the diagram, it consists of two dynamos connected in series and a system of wiring of one positive +, one nega- tive — and a neutral ^ wire. So long as an equal number of 34 MODERN ELECTRICAL CONSTRUCTION. lights are burning on both sides of the neutral wire, this wire carries no current, but should more lights be in use on one side of the system than on the other, the neutral wire will be called upon to carry the ditference. If all the lights on one side are out, the dynamo on that side will be running idle. The currents in the neutral wire may be either positive or negative in direction. The principal advantage of this sys- tem is that with it double the voltage of the 2-wire systems is employed and yet the voltage at any lamp is no greater than with the use of two wires. It is customary to use 110 volts on each side of the neutral wire and this gives a total volt- age over the two outside wires of 220 volts. As the same current passes ordinarily through two lamps in series, we need, for a given number of lamps only half as much current as with 2-wire systems and can, therefore, use smaller wires. For the same number of lights and the same per- Figure 17 centage of loss the amount of copper required in the two outside wires is only one-foujrth that of 2-wire systems; to this must be added a third wire of equal size for the neutral, so that the total amount of copper required with this system is ^ of that of 2-wire system using the same kind of lamps. Incandescent lamps are often run in multiple-series, as in WIRING SYSTEMS. 35 Figure 17, without a neutral wire. The number of lamps to be used in series depends upon the voltage of the dynamo. If that is 550, five 110 volt lamps are required in each group, 3r ten 55 volt lamps. If the filament of one lamp breaks all of the lamps in ^^^^^^ 9 rO- -O- -O- -O- UUc^<^ ■o-J Figure 18 that group are extinguished and if one is to be used all must be used. Figure 18 shows the diagram of a series-multiple system. This style of wiring should be avoided. A diagram of an alternating current system is shown in w Figure 19 Figure 19. In this system extremely high voltage is used and consequently the currents are never very great. This makes 36 MODERN ELECTRICAL CONSTRUCTION. it extremely useful for long distance transmission. Since, however, the high pressure employed cannot be used directly in our lamps it must be transformed into lower pressure. This is done by means of transformers, and it is possible to reduce the line voltage to any desirable extent. As the volt- age is reduced, however, the current increases and the wires taken from the transformers into the buildings must be as large as those for 2-wire systems using the same kind of lamps. The high pressure, or primary wires, are rarely allowed inside of buildings. The Transmission of Electrical Energy. We have seen that currents of electricity flow only in electrical conductors, and that these conductors are usually arranged in the form of wires. We have further seen that the power transmitted is proportional to the product of the volts and amperes used. The actual amount of energy trans- mitted being the product of the above multiplied by the time. Currents of electricity always encounter some resistance and in consequence of this resistance, generate heat; the generation of heat in any electric circuit being proportional to the square of the current multiplied by the resistance. This formula, P X R expresses the loss of electrical energy due to the resistance of the conductors and which reappears in the form of heat. If this loss is not kept within reasonable limits, the wires will become very hot and destroy the in- sulation or ignite surrounding inflammable material. The above loss and hazard is generally guarded against by insur- ance companies and inspection boards by designation of the current in amperes which certain wires may be allowed to carry. Table No. 1 gives the currents which the National Board of Fire Underwriters has decided to consider safe and which ELECTRICAL TRANSMISSION 37 should be closely followed, and on no account should wires smaller than those indicated be used. There is no harm and no objection to using wires larger than indicated, but neither is there much gained unless the run be a long one as we shall see further on. The table of carrying capacities shows a great discrepancy between the relative cross-section of large and small wires and the currents they are allowed to carry; thus a No. 0000 wire has a cross-section about eight times as great as that of No. 6, yet is allowed to carry less than five times as much. This discrepancy arises from the different rate of heat radiation. The radiating surface or circumference of a small circle or wire is relatively to its cross-section much greater than that of a large circle, and other things being equal the ratio existing between the heat given to a body and its radiat- ing surface determine its temperature. We have seen before that the power (either for lights or motors) consists of two factors; current and pressure, ex- pressed respectively as amperes and volts. We have also seen that the power (watts) equals the product of these two; hence it follows, that as we increase either one, we may de- crease the other, or conversely, as one is decreased the other must be increased in order to deliver a given amount of power. We further know that it is the current alone which heats the wires and that accordingly as our currents are large or small, the wires used to transmit them must be large or small. It is obvious, therefore, that we can save much on copper by using higher voltages, since, if we double the voltage, we shall need only one-half as much current and can, therefore, use a much smaller wire. As an example : Sup- pose we have power to transmit which at 110 volts requires 90 amperes. This requires a No. 2 wire containing 66,370 circular mils. Now, if we double the voltage, we shall need only 45 amperes; this much we are allowed to transmit over 38 MODERN ELECTRICAL CONSTRUCTION. a No. 6 wire which has only 26,250 circular mils. We must not, however, increase our voltage without due precaution and consideration, for high voltage is dangerous to life and in- creases the fire hazard. It also increases the liability to leakage and requires better and more expensive insulation which in a small measure offsets the other advantages. The usual voltage employed at present varies from 110 to 220 volts for indoor lighting and power; 500 to 650 volts for street railway work and from 2 to 20,000 volts for long distance transmission. The higher voltages mentioned are seldom brought into buildings, and are nearly always used with some transforming device which reduces the pressure to 110 or 220 volts for indoor lighting or power. The flow of current through a given lamp, motor, or re- sistance determines the light, power or heat obtainable from such device. We know that the flow of current in turn (other things being equal) varies as the E. M. F. maintained at the terminals of any of these devices. Consequently in order to obtain a steady flow of current it is necessary to provide a steady E. M. F. The loss of E. M. F. in any wire is equal to the current flowing in that wire multiplied by the resistance of the wire. Since it is impossible to obtain wires without resistance, it is also impossible to establish a circuit without loss and wherever electricity is used some loss must be reckoned with. We may make this loss as large or as small as we desire. Where the cost of fuel is high, it is important to keep this loss quite small, using for that purpose larger wires. On the other hand where there is an abundance of cheap fuel, or, where, for instance, water power is used, it will be more economical to waste five or ten per cent of the electrical energy than to spend the money needed to provide the copper necessary to reduce the waste to one or two per cent. In this connection, however, it must not be overlooked that ELECTRICAL TRANSMISSION 39 the quality of the service depends to a great extent upon the loss allowed and here the nature of the business supplied must be taken into consideration. In yards, warehouses, barns, etc., a variation of five or ten per cent in candle power may not matter much, but in residences or offices it is very annoying. The loss in voltage depends, as we have already seen, upon the current used, and the resistance of the wire em- ployed. If the current is decided upon, we can reduce the loss only by reducing the resistance ; the resistance can be re- duced only by increasing the size of wire used. If we double the cross-section of the wire, we decrease the resistance one- half and consequently reduce the loss or variation in volt- age one-half. Thus it will be seen that as we attempt to reduce the loss in voltage to a minimum we shall require very large wires and thus greatly increase the cost of our installation. For instance, if a line be in operation with a loss ^f twenty per cent, by doubling the amount of copper, we reduce the loss to ten per cent. In order to reduce our loss to five per cent, we must again double the amount of copper; and to reduce the loss still more, say to 2>4 per cent, a wire of double the cross-section of the last must be used. If the cost of copper in the original installation utilizing eighty per cent of the energy be taken as 1, then the cost of copper to utilize ninety per cent will be 2; of ninety-five per cent, 4; and of ninety-seven and one-half per cent, 8; and no amount of copper will ever be able to save the full 100 per cent. We must not overlook, however, that although a reduction of loss from four to two per cent requires us to double the amount of copper, it does not necessarily double the cost of our installation, for in many cases it adds but a small per- centage to the total cost. For Instance, if it were decided to use No. 12 instead of No. 14 wire in moulding or insulator 40 MODERN ELECTRICAL CONSTRUCTION. work, the cost of labor would not be appreciably affected thereby; similarily in connection with a pole line, the dif- ference in total cost occasioned by the use of say No. 6 instead of No. 10 wire would be small. Calculation of Wires. In electrical calculations so far as they relate to wiring, the circular mil plays an important part, and it becomes necessary to thoroughly understand its meaning. The mil is the 1/1000 part of an inch, consequently one square inch contains 1,000x1,000 equals 1,000,000 square mils. If all elec- trical conductors were made in rectangular form, we should be able to get along nicely by the use of the square mil, but, since they are nearly all in circular form, the use of the square mil as a unit would necessitate otherwise unnecessary figures. The circular mil means the cross-section of a circle one mil in diameter, whereas the square mil means a square each side of which is equal to one mil in length. Square mils, can, therefore, be transformed into circular mils by dividing by .7854, and circular mils into square mils by multiplying by .7854, since it is well known that a circle which can be inscribed within a square bears to that square the ratio of .7854 to 1. To illustrate : Using square mils if we wish to determin*? the cross-section of a wire having a diameter of 50 mils, we must first square the diameter and then multiply by .7854; 50 X 50 X .7854, or 1963.5, which is the cross section of the wire expressed in square mils. To express the cross-section in circular mils, we have but to square the diameter, or 50 X 50 = 2500 circular mils. The 2500 circular mils are exactly equal to the 1963.5 square mils. The adoption of the circular mil simply eliminates the figure .7854 from the calculations. The resistance of a copper wire having a cross-section of CALCULATION OF WIRES ^' one mil and a length of one foot is from 10.7 to 10.8 ohms, .he variation being due to the temperature of the wire. 10.8 ohms is the resistance usually taken. This resistance in- creases directly as the length and decreases as the cross-sec- tion increases. The resistance of an}^ copper wire can, there- fore, be found by multiplying its length by 10.8 and dividing by the number of circular mils it contains. Expressed in L X 10.8 formula this becomes R = where L stands for the C. M. total length of wire in feet, and C. M. for the cross-section in circular mils, and R for the resistance in ohms. In order to find the loss in volts, we must multiply the resistance by the current used. Representing this current by I, the I X L X 10.8 formula becomes = V; V being the volts lost. C. M. It is, however, seldom necessary to find how many volts would be lost with a certain wire and current, but rather to find how many circular mils are necessary in a wire so that the volts lost may not exceed a certain percentage. In order to determine this, we transpose V and C. M. and the formula now becomes I X L X 10.8 = C, M. This is the final formula and gives V directly the number of circular mils a wire must have so that the loss with this current and length of wire shall not exceed the limits set by V. As an example, we have a current of 20 amperes to trans- mit a distance of 200 feet and the loss shrJl not exceed two per cent; voltage 110. This requires 400 feet of wire (two wires 200 feet long) and two per cent of 110 is 2.2. We therefore have 20 X 400 X 10.8 divided by 2.2, which gives us 39,270 circular mils, which we see by table I is a little less than a No. 4 wire. 42 MODERN ELECTRICAL CONSTRUCTION. The above formula will answer for all 2-wire work^ whether it be lights or power. It is simply necessary to find the current required with whatever devices are to be used. These calculations are not often made in actual practice. It is much easier to refer to tables such as II. Ill, IV, V, Vl, given at the end of this volume, by which the proper size of wire can be determined at a glan^^e almost. In connection with 3-wire systems using two lamps in series, we need to calculate the two outside wires only, the neutral wire should then be taken of the same size. We must however assume double the voltage existing on either side of the neutral; that is to say, a 2-wire system using 110 volts would be figured at 110 volts, while a 3-wire system, using 110 volt lamps on each side of the neutral wire would be figured at 220 volts. It must also be noted that with 3-wire systems the cur- rent required is only Yz of that required with 2-wire sys- tems. Ordinarily we have two lamps in series and the same current passes through both. Applying this to our formula we see that with the 3-wire system* the current I is only half as great as with 2-wire systems and (the percentage of loss in both cases being the same) V, which stands for the volts to be lost, becomes twice as great. Owing to these two fac- tors, the wire for 3-wire systems need have only ^ as many circular mils as that of a 2-wire system with the same per- centage of loss. To this must be added the neutral wire so that the total cost of wire must be Yz of that for the 2-wire systems. The amount of copper required in power transmission for a given percentage of loss varies as the square of the voltage employed. By doubling the voltage we can transmit power with the same loss four times as far; or, if we do not change distance or wire, we shall have only one-fourth of the loss CALCULATION OF WIRES 43 we had before. A practical idea of the laws governing the distribution of circuits and the losses in voltage and wire which are unavoidable may be gained from Figure 20. Figure 20 shows 96 incandescent lights arranged on one floor and placed 10 feet apart each way. With all cutouts placed at A and circuits arranged as in No. 1, 2,080 feet of branch wiring for the eight circuits of 12 lights each, will be required. If the cutouts be placed in the center, B, the same length of wire will be necessary. We have in this case merely transferred the cross wires from one end of the hall to the center. If we arrange two sets of cutouts as at C and D and run circuits as 3 and 4 the total amount of wire necessary will be only 1,920 feet. By this arrangement we avoid the necessity of crossing the space indicated by dotted lines at the right, opposite B. If we run the circuits on the plan of No. 2, the least amount of wire for the eight circuits will be 2,560 ft. Such wir- ing would require extra wires feeding the various groups. Should we run a set of mains along ACBD, and make 12 circuits of the installation by placing one cutout for each eight lights, the amount of wire required will be 1,680 feet. If we run a set of mains through B as shown by dotted lines using 12 lights per circuit, 1,760 feet of wire will be re- quired. If we now double the number of lights in the same space or limit the number per circuit to six, we shall require 3,200 feet of wire to feed them all from A, but only 2,400 to feed them from B ; to feed them all from the two centers C and D will also require 2,400 feet. The most economical location of cutout centers will, with even distribution of light, and in regard to branch wiring only, be such that it is unnecessary to run circuits like No. 2; in other words, not more than the number of lights allowed on one circuit should lead away from it in one direction. Suppose, for instance, the number of lights be increased 44 MODERN ELECTRICAL CONSTRUCTION. gc §0 o o o o o o o o o o / • 9 I09;l? I09.Z 5 o oxDra n () — n () O ZX) () () ) () a 0- yvvQ" Figure 25. should be placed in those leads w^hich feed into the positive and negative mains, Figure 25. They should not be placed in 54 MODERN ELECTRICAL CONSTRUCTION. the equalizer lead or in the lead connected to the series field for the reasons already given. It will be noticed that the two generators shown at the right of the diagram are con- nected in a reverse manner from those at the left. An ex- amination of the diagram, Figure 26, will show the reason for -QvvJ hO^aa. -r>v\) Kl)vv\ Figure 26. this. In this case the placing of the fuse in the lead not affected by the equalizer current brings it in the lead con- nected to the neutral bus. If, with the fuse located in this line, the generator winding should become grounded a short circuit would result, as the neutral wire is always grounded, current flowing from the positive bus bar through the positive lead and the wires on the generator to the ground. The gen- erator would have absolutely no protection in a case of this kind and a fire would be sure to result. If the fuses were placed in the outside leads the circuits would be immediately opened and current shut off from the machine. Figures 27, 28 and 29 show the proper location of fuses in three-wire, direct current generator installations. In Fig- ure 27 is shown the wiring connection of a three-wire direct current generator. The armature of this generator contains GENEKATORS. 55 two separate armature windings, each winding being provided with its own commutator, located on each side of the arma- ture. Two separate series field windings are provided, each ir 5 Figure 27. field winding being connected in series with an armature wind- ing. The shunt field connections are not shown. To comply with the requirements each generator should be connected to the bus bars and fuses installed as shown. The simplified diagram. Figure 30, shows in a plainer manner the reason for this arrangement. Referring to the connections shown it will be seen that .the fuses protect each armature winding both from overload or from possible shorts caused by the grounding of the armature windings. A wrong ar- rangement of the fuses, and one that should be avoided, is shown in the diagram, Figure 31. In this case fuses are in- stalled in the lead from the series winding. The first objec- tion to this arrangement is the one which has already been explained, i. e., the current from the armature having two paths open to it, one through the series field and one through 56 MODERN ELECTRICAL CONSTRUCTION. the equalizer, .the armature could generate an excessive cur- rent without the fuse, which may be carrying only a part of the current, blowing. If for any reason one of the fuses shown did blow serious conditions might result owing to the fact that the armature of that machine is still connected to the armatures of all the remaining machines through the equalizer bus. A double-pole circuit breaker so arranged as to open both the series field lead and the equalizer lead would remove this objection, but, as the circuit breaker would be actuated by the current in the series field lead the objections before Fig-ure stated still exist. Locating the fuse in the armature lead con- nected to the neutral bus would leave the generator unpro- tected in case of grounds. Figure 28 shows the connections of the Westinghouse direct current, three-wire generator. In this generator direct cur- rent at the potential of the outside mains, usually 220 volts, is taken off the commutator side while the neutral connection is made through auto transformers to slip rings on the opposite GENERATORS. 57 side of the armature shaft. Two separate series field windings are connected in series with each direct current armature lead. In order to place a fuse in each direct current armature lead, fuses would have to be mounted on the generator itself or the leads would have to be carried from the armature brushes to the switchboard and back to the series field. The usual pro- tection provided with this generator consists of double-pole, double-trip circuit breakers connected in the leads from the series fields and corresponding equalizer connection, this cir- cuit breaker being actua.ted by the current in the lead from the series field and arranged to open both series field and equalizer leads. As this generator is designed to withstand only a 25 per cent overload the circuit breakers should be interconnected so that in case one generator lead opens it automatically opens the remaining lead. Figure 29 shows the wiring connections of a compensator Fignre 29. set. This set consists of two machines, the armature shafts of which are rigidly connected together. Each machine acts as 58 MODERN ELECTEICAL CONSTBUCTION. a motor or generator, depending on the condition of unbal- ance ; and they are used only to balance the system, other gen- erators supplying current to the outside mains. This class of apparatus is protected in the same manner as in the case just described. A double-pole, double-trip cir- cuit breaker should be installed in each outside lead and cor- d . ■-i ± L ■? Figure 30. Figure 31. responding equalizer lead. It might be well to state that with apparatus designed on the principle just described various details of construction of the machines, as built by the dif- ferent manufacturers, require a more complicated system of protection so that the above rule is not always exactly com- plied with. Circuit breakers, when used for protection in dynamo leads, are generally mounted on the switchboard and con- nected in the circuit ahead of the main switch. The circuit breaker as at present constructed is, in nearly all cases, a much more efficient and reliable device than the fuse, and its use is to be recommended. The fusing point of an ordinary fuse depends on the temperature of the fuse metal. When fuses are used in an engine room where the temperature is often very high the fuse may blow when it is carrying a cur- rent very much less than its rated capacity, and this will gen- erally result in a larger fuse being installed. The circuit GENEEATOES. 59 breaker is no.t affected by this increase in temperature. When a fuse blows from overload it generally occurs at a time when all the apparatus is in use and serious delays are apt to result before the fuse can be replaced. This objection does not exist where the circuit breaker is used. As to the relative currents at which the fuse and circuit breaker should be set to operate, authorities differ. Some ad- vise that both be set to operate at the same current strength so that the fuse, which takes a longer time to operate, will blow only in case the circuit breaker fails. Another recom- mends that the fuses be of such capacity as to carry any load which will be required of them and to set the circuit breaker a little higher than the fuses so that the fuses will operate on overload and the circuit breaker on short circuit. The prac- tice of setting the fuses at about 25 per cent above the circuit breaker seems to be preferred, for it frequently happens, when both are set to operate at the same current strength, the fuse alone will "blow," due to the excessive heat produced in the fuse at full load. There is a tendency in the design of some of the newer generators to do away with binding posts, leads properly bushed through the generator frame and arranged for direct connection to leads from switchboard being provided instead. As this does away with exposed, live parts it is to be recom- mended. Where there are exposed live parts on the genera- tor or its connections they should be protected from accidental contact, except where they are at the same potential as the ground, as in the case of the neutrals on the direct current three-wire systems and the ground return on trolley systems. Cases are sometimes found where the cessation of current due to the blowing of a fuse could cause more damage than would result from an overload, as, for instance, where the 60 MODERN ELECTRICAL CONSTRUCTION. dynamo operates some safety device. In cases of this kind the Inspection Department having jurisdiction may modify the requirements. e. Must each be provided with a name-plate, giving the maker's name, the capacity in voUs and amperes, and the normal speed in revolutions per minute. f. Terminal blocks when used on generators must be made of approved non-combustible, non-absorptive insulating material, such as slate, marble or porcelain. 2. Conductors. From generators to switchboards, rheostats or other instru- ments, and thence to outside lines. a. Must be in plain sight or readily accessible. Wires from g-enerator to switchboard may, however, be placed in a conduit in the briclt or cement pier on which the generator stands, provided that proper precautions are talcen to protect them against moisture and to thoroughly insulate them from the pier. If lead-covered cable is used, no further protection will be required, but it should not be allowed to rest upon sharp edges which in time might cut into the lead sheath, especially if the cables were liable to vibration. A smooth runaway is desired. If iron conduit is provided, double braided rubber-covered wire (see No. 47) will be satis- factory. h. Must have an approved insulating covering as called for by rules in Class "C" for similar work, except that in cen- tral stations, on exposed circuits, the wire which is used must have a heavy braided, non-combustible outer covering. Bus bars may be made of bare metal. Rubber insulations ignite easily and burn freely. Where a number of wires are brought close together, as is generally the case in dynamo rooms, especially about the switchboard, it is therefore necessary to surround this inflammable ma- terial with a tight, non-combustible outer cover. If this is not done, a fire once started at this point would spread rapidly along the wires, producing intense heat and a dense smoke. Where the wires have such a covering and are well Insulated and supported, using only non-combustible materials, it is believed that no appreciable fire hazard exists, even with a large group of wires. Flame proofing should be stripped back on all cables a sufficient amount to give the necessary insulation distances for the voltage of the circuit on which the cable is used. The stripping back of the flame proofing is ne.cessary on account CONDUCTORS. 61 of the poor insvilating- qualities of the flame proofing- material now available. Flame proofing- may be omitted where satis- factory fire proofing- is accomplished by other means, such as compartments, etc. c. Must be kept so rigidly in place that they cannot come in contact. d. Must in all other respects be installed with the same precatitions as required by rules in Class "C" for wires carry- ing a current of the same volume and po.tential. e. In wiring switchboards, the ground detector, voltmeter, pilot lights and potential transformers must be connected to a circuit of not less than No. 14 B. & S. gage wire tha.t is protected by an approved fuse, this circuit is not to carry over 660 watts. For the protection of instruments and pilot lights on switchboards, approved N. E. Code Standard Enclosed Puses are preferred, but approved enclosed fuses of other designs of not ovpr two (2) amperes capucity may he used. Voltmeter switches having- concealed connections must be plainly marked, showing- connections made. A number of different methods are used for running wires in d^mamo rooms. Where the dynamo is located in a room with a low ceiling, or where it is not desirable to run the wires open, metal conduits may be imbedded in the floor and the wires run in them. If the engine room is located in the basement or in any place where water or moisture is liable to gather in the conduits the wires should be lead covered. At outlets the conduits should be carried some distance above the floor level and close to the frame of the machine, where they will be protected from mechanical injury. If the space under the machine will allow it, the conduit should be ended there where it will be protected by the base frame. Where lead covered, wires are used, the lead should be cut back some distance from the exposed part of the wire and the end of the lead should be well taped and compounded so that no moisture can creep in between the lead and the insulation. In place of .the metal conduits tile ducts can be used ; or, if the floor is of cement, a channel may be left in the floor 62 MODERN ELECTRICAL CONSTRUCTION. and the wires run into it. A removable iron cover should be provided. The wires may be run open on knobs or cleats as described in Class C. Where there are many wires, cable racks, con- structed of wood or preferably iron, having cleats bolted to them, may be used. As a general rule moulding should not be used for this class of work. Especially in central stations the generators are often called upon for a very heavy overload and should the wires becom.e overheated a fire is much more apt to result when the leads are run in moulding than if they were run open where any trouble could be immediately no- ticed. 3. Switchboards. a. Must be so placed as to reduce to a minimum the danger of communicating fire to adjacent combustible material. Special attention is called to the fact that switchboards should, not be built down to the floor, nor up to the ceiling. A space of at least ten or twelve inches should be left between the floor and the board, except when the floor about the switchboard is of concrete or other fireproof construction, and a space of three feet, if possible, between the ceiling and the board, in order to prevent fire from communicating from the switchboard to the floor or ceiling, and also to prevent the forming of a partially concealed space very liable to be used for storage of rubbish and oily waste. h. Must be made of non-combustible material or of hard- wood in skeleton form, filled to prevent absorption of moisture. If wood is used all wires and all current-carrying parts of the apparatus on the switchboard must be separated therefrom by non-combustible, non-absorptive insulating material. c. Mus.t be accessible from all sides when the connections are on the back, but may be placed against a brick or stone wall when the wiring is entirely on the face. If the wiring is on the back, there should be a clear space of at least 18 inches between the wall and the apparatus on the board, and even if the wiring is entirely on the face it is much better to have the board set out from the wall. The space back of the board should not be closed in, except by grating or netting either at the sides, top or bottom, as such an enclosure is almost sure to be used as a closet for clothing SWITCHBOARDS. or for the storage of oil cans, rubbish, etc. An open space is much more likely to be kept clean, and is more convenient for making- repairs, examinations, etc. d. Must be kept free from moisture. e. On switchboards the distances between bare live parts Figure 32. of opposite polarity must be made as great as practicable, and must not be less than those given for tablet-boards (see No. 53 A). The switchboard may be located in any suitable place in the dynamo room. It should generally be placed in a central position as close as possible, without inconvenience, to all machines and perfectly accessible. Do not locate a switch- 04 MODERN ELECTRICAL CONSTEtCTION. board under or near a steam or water pipe or too close to windows, as these may accidentally be the means of wetting the board. The ma.terial generally used for the construction of switch- boards is slate or marble, free from metallic veins. If metallic veins are not guarded against they may cause great leakage of current, which will manifest itself in heating the slate or marble. The switchboard may be made of hardwood in , skeleton form (see Figure 32), but in this case all switches, cutouts, instruments, etc., must be mounted on non-combustible, non- absorptive insulating bases, such as slate or marble and all wires must be properlv bushed where they pass through the woodwork and must be supported on cleats or knobs. Wood base instruments are not approved. Marble or slate boards are usually set in angle iron frames and are much safer and better than the skeleton board shown. It is a good plan to have the iron legs rest on a wooden base, so that they will be insulated from the ground. Although only 18 inches clear space is required back of the board, where the board is back connected, this should be increased wherever possible, especially in the case of large boards. 4. Resistance Boxes and Equalizers. (For construction rules, see N'o. 6o.) a. Must be placed on a switchboard or, if not .thereon, at a distance of at least a foot from combustible material, or separated therefrom by a non-inflammable, non-absorptive insulating material such as slate or marble. This will require the use of a slab or panel of non-com- bustible, non-absorptive insulating material such as slate or marble, somewhat larger than the rheostat, which shall be secured in position independently of the rheostat supports. Bolts for supporting- the rheostat shall be countersunk at least % inch below the surface at the back of the slab and RESISTANCE BOXES. filled. For proper mechanical strength, slab should be of a thickness consistent with the size and weight of the rheostat, and in no case to be less than y^ inch. If resistance devices are installed in rooms where dust or combustible flyings would be liable to accumulate on them, they should be equipped with a dust-proof iiace plate. Ordinarily the dynamo field rheostat is mounted on the back of the board if the board is back connected, a small hand wheel being provided so that the rheostat may be operated from the front of the board. If the switchboard is in skele- ton form, or if the rheostat is placed on a wall, it should be mounted on a solid piece of slate or marble. Separate screws should be used for at- taching the rheostat .to the slate Figure 33. or marble and the slate or marble to the wall, for, if the same screws were used for this purpose, they would be apt to ground the rheostat frame. (See Figure 33.) On central stations where current is furnished over a large area, there is on some of the circuits, especially the long ones, a considerable "drop," or loss of potential. In order to keep the voltage at the point of supply on these circuits at the proper value, the voltage at the station must be raised. This in turn causes the voltage on those circuits near the dynamo to become excessive. Equalizers, which are large resistance boxes generally constructed of iron wire or strips, and capable of carrying a heavy current, are connected in the circuits and adjusted at such resistances as to make the voltage at the various points of supply uniform. They are generally too heavy to mount on the board, but should be raised on non- combustible, non-absorptive insulating supports and should be separated from all inflammable material. 6b MODERN ELECTRICAL CONSTRUCTION. b. Where protective resistances are necessary in connec- tion with automatic rheostats, incandescent lamps may be used, provided that they do not carry or control the main current or constitute the regulating resistance of the device. When so used, lamps must be mounted in porcelain recep- tacles upon non-combustible supports, and must be so arranged that they cannot have impressed upon them a voltage greater than that for Mfhich .they are rated. They must in all cases be provided with a name-plate, which shall be permanently at- tached beside the porcelain receptacle or receptacles and stamped with the candle-power and voltage of the lamp or lamps to be used in each receptacle. c. Wherever insulated wire is used for connection be- tween resistances and the contact plate of a rheostat, the insu- lation must be slow burning (see No. 43). For large field rheostats and similar resistances, where the contact plates are not mounted upon them, the connecting wires may be run together in groups so arranged that the maximum difference of potential between any two wires in a group shall not exceed 75 volts. Each group of wires must either be mounted on non-combustible, non-absorptive insulators giving at least J/j inch separation from surface wired over, or, where it is neces- sary to protect the wires frorn mechanical injury or moisture, be run in approved lined conduit or equivalent. 5. Lightning Arresters. (For construction rules, see No. 63.) a. Must be attached to each wire of every overhead cir- cuit connected with the station. It is recommended to all electric lig-ht and power companies that arresters be connected at intervals over systems in such numbers and so located as to prevent ordinary discharges en- tering- (over the wires) buildings connected to the lines. b. Must be located in readily accessible places away from combustible materials, and as near as practicable to the point where the wires enter the building. In all cases, kinks, coils and sharp bends in the wires be- tween the arresters and the outdoor lines mus.t be avoided as far as possible. The switchboard does not necessarily afford the only loca- tion meeting thes^ requirements. In fact, if the arresters LIGHTNING ARRESTERS. 67 can be located in a safe and accessible place away from the board, this should be done, for in case the arrester should fail or be seriously damaged there would then be less chance of starting arcs on the board. c. Must be connected with a thoroughly good and perma- nent ground connection by metallic strips or wires haying a conductiyity not less than that of a No. 6 B. & S. gage copper wire, which must be run as nearly in a straight line as possible from the arresters to the ground connection. Ground wires for lightning arresters must not be attached to gas pipes within the buildings. It is often desirable to introduce a choke coil in circuit between the arresters and the dynamo. In no case should the ground wires from the lightning arresters be put into iron pipes, as these would tend to impede the discharge. d. All choke coils or other attachments, inherent to the lightning protection equipment, shall haye an insulation from the ground or other conductors equal at least to the insulation demanded at other points of the circuit in the station. A lightning discharge is simply a discharge of electricity at very high potential. While the insulation of the ordinary wire seryes yery well for the yoltages for which it is used it offers yery little resistance to a current of such high potential, and providing the discharge can reach the ground VWWWVWx/'^/xA/ by jumping through the insula- /VWWWVWWV\ tion it will generally take that course unless some easier path is offered to it. A lightning arrester in its simplest form consis.ts of pjg. 34 two metal plates separated by a small air space as shown in Fig- ure 34. One of the plates is con- nected to the line and the other to the ground, a set being pro- vided for each line wire to be protected. The air space between the metal plates offers a much lower 68 MODERN ELECTKICAL CONSTEUCTION. resistance to the passage of such a sudden current as a dis- charge of Hghtning consists of, than do the magnets of a d3mamo, for instance, or highly insulated parts of the line. The current, therefore, jumps the air space and passes to ground. When the current jumps .this air space it produces an arc similar to that seen in an arc lamp, and after the light- ning discharge is over the dynamo current is very likely to maintain this arc and thus cause a short circuit from one lightning arrester through the ground to the other. Different methods of preventing this by interrupting the arc have been devised. Figure 35 shows the T. H. Hghtning arrester, in which the arc is extinguished by a magnetic field set up by the elec- tro-magnet. In the Wurts non-arcing lightning arrester (Fig- ure 36) the discharge takes place across the air gaps between the cylinders ; these are made of a metal which will not arc. A choice coil is simply a coil of wire, the size of wire and the number of turns depending upon the normal current and voltage of the system on which it is used. On 500 volt street railway circuits the choke coil sometimes consists of a spiral of five or six turns of heavy copper rod, while on high po- tential, alternating current circuits a greater number of turns and smaller wire is used. As every coil of wire has a certain amount of inductance, or, in other words, tends to hold back any change in the E. M. F., the placing of a coil in the cir- cuit between the lightning arrester and the apparatus on which the current is used affords a pro.tection to the apparatus and forces the lightning discharge to pass to the ground through the lightning arrester. • As the lightning arrester and choke coil are subjected to extremely high potentials they should be carefully insulated and properly located. 6. Care and Attendance. a. A competent man must be kept on duty where gen- erators are operating. Figure 35. b. Oily waste must be kept in approved metal cans and removed daily. Approved waste cans shall be made of metal, with legs raising can 3 inches from the floor and with self-closing covers. 7. Testing of Insulation Resistance. a. All circuits except such as are permanently grounded in accordance with Rule 13 A must be provided with reliable ground detectors. Detectors which indicate continuously and give an instant and permanent indication of a ground are preferable. Ground wires from detectors must not be at- tached to gas pipes within the building. b. Where continuously indicating detectors are not feasi- MODERN ELECTRICAL CONSTRUCTION. ble the circuits should be tested at least once per day, and preferably oftener. c. Data obtained from all tests must be preserved for ex- e ^ M «^ rm «TM — m. v^ Figure 45. where either inflammable gases or dust exist. If a starting box is to be located in a room where considerable dirt is apt to gather, or if the room is unusually damp, the starting box should be mounted in a dus.t-tight fire-proof box, which should be kept dosed at all times, except when starting the motor. If the enclosing box is rather large, sufficient venti- lation of the coils will be obtained while the motor is being started and .the door open. A speed controller should never be mounted in an enclosure unless the same is arranged to give a thorough ventilation to the outside air, as heat is con- stantly being generated in the coils of the rheostat, and this heat must be dissipated. A speed controller should never be located where dust or lint is apt to gather on it. If it is necessary to use one on a motor located in such a place, it should be mounted outside the room. In metal working establishments or in any place where there is a liability of the contacts on the switches or the starting boxes being short-circuited, they should be enclosed or suitably protected. e. Must not be run in series-multiple or multiple-series, except on constant-potential systems, and then only by special permission of the Inspection Department having jurisdiction. Figure 45 shows a series-multiple, and Figure 46 a multiple- series system of wiring. /. Must be covered with a waterproof cover when not in Figrure.46. use, and, if deemed necessary by the Inspection Department having jurisdiction, must be enclosed in an approved case. When it is necessary to locate a motor in the vicinity of 86 MODERN ELECTEICAIi CONSTRUCTION. combustibles or in wet or very dusty or dirty places, it is generally advisable to enclose it as above. Such enclosures should be readily accessible, dust proof and sufficiently ventilated to prevent an excessive rise of temperature. The sides should preferably be made largely of glass, so that the motor may be always plainly visible. This lessens the chance of its being neglected, and allows any derangement to be at once noticed. The usq of enclosed type ; motor is recommended in dusty places, being preferable to wooden boxing. From the nature of the question the decision as to details of construction must be left to the Inspection Department having jurisdiction to determine in each instance. Under certain conditions it is found necessary to enclose motors in dust-tight enclosures. The practice of building a small box which fits entirely around the motor, enclosing the pulley and provided with slots .through which the belt passes, is very unsatisfactory. While this construction prevents con- siderable dust from settling on and around the motor, still a great deal will be carried in by the belt. If the box is so made that it fits tightly around the shaft between the pulley and the motor frame and is otherwise well constructed, most of the dust and dirt can be kept out. As the efficient work- ing of the motor requires that it be kep.t as cool as possible, the box should afford sufficient ventilation- This may be obtained by making the box somewhat larger than the motor, thus allowing the heat to radiate from the sides, or the boxes should be ventilated to the outside air. A number of motors are so constructed that, by means of hand plates, they can be entirely enclosed. When they are so enclosed their efficiency and capacities are somewhat reduced, but cases are sometimes found where the conditions require motors of this kind to be used. In places where there is considerable dust flying about in the air, and where the dust is not readily combustible, a fine gauze can be used to close the hand holes. This gauze will allow ventilation, bu.t will prevent the dirt from gathering MOTORS. 87 inside the motor. The alternating induction motors, which are operated without brushes or collector rings, can be used in almost any location, as there is no sparking. g. Must, when combined with ceiling fans, be hung from insulated hooks, or else there must be an insulator interposed between the motor and its support. Ceiling fans are generally provided with an insulating knob on which the fan hangs. If this is not provided, a sim- ple knob break can be used, or the fan can be suspended from a hook screwed into a hardwood block, provided the hook does not pass through the block into .the plaster, the block being separately supported from the ceiling. h. Must each be provided with a name-plate, giving the maker's name, the capacity in volts and amperes, and the nor- mal speed in revolutions per minute. 1 i. Terminal blocks when used on motors must be made of approved non-combustible, non-absorptive insulating ma- terial such as slate, marble or porcelain. y. Variable speed motors, unless of special and appro- priate design, if controlled by means of field regulation, must be so arranged and connected that they cannot be started under weakened field. The speed of a motor may be changed either by inserting resistance in series with the armature, thereby cutting down the voltage at the armature terminals; or by decreasing the field current through the addition of resistance in series with the shunt field winding. By this latter method the lines of force passing through the armature gap are considerably decreased and the armature must therefore revolve at a greater speed to develop the proper counter electro-motive force. When a motor is started under a weakened field, the starting torque being reduced, the armature is slow in coming up to speed. This prevents the rapid rise of counter E. M. 88 MODERN ELECTRICAL CONSTRUCTION. F. which takes place in the ordinary motor and consequently the heavy rush of current through the armature is more likely to continue and burn out the armature. Unless motors are so designed that they do not require this excessive current when starting under a weakened field, the field rheostat, if separate from the starting rheostat, must be provided with a no-voltage release, such as is described in figure 41. When the field rheostat is combined with the starting rheostat the apparatus should be so constructed that Figure 47 the motor cannot be started under a weakened field. Figure 47 shows a starting rheostat of this kind, the last four con- tacts at the right being connected to the shunt field resistance. Moving the rheostat arm to the right cuts this resistance in series with the shunt field. 9. Railway Power Plants. a. Each feed wire before it leaves the station must be equipped with an approved automatic circuit breaker (see No. 52) or other device, which will immediately cut off the current TEANSFOEMEKS. in case of an accidental ground. This device must be mounted on a fireproof base, and in full view and reach of the attend- ant. 10. Storage or Primary Batteries. a. When current for light or power is taken from pri- mary or secondary batteries, the same general regulations must be observed as apply to similar apparatus fed from dynamo generators developing the same difference of poten- tial. b. Storage battery rooms must be thoroughly ventilated. c. Special attention is directed to the rules for wiring in rooms where acid fumes exist (see No. 24 i and ;). d. All secondary batteries must be mounted on non-ab- sorptive, non-combustible insula.tors, such as glass or thor- oughly vitrified and glazed porcelain. e. The use of any metal liable to corrosion must be avoided in cell connections of secondary batteries. Rubber-covered wire run on glass knobs should be used for wiring storage battery rooms. The knobs should be of such size as to keep the wire at least one inch from the surface wired over, and they should be separated 2^4 inches for voltage up to 300 and 4 inches for voltage over 300. Water- proof sockets hung from stranded rubber covered wire and properly supported independently of the joints should be used ; these lights to be controlled by a switch placed out- side of battery room. All joints after being properly sold- ered and taped with both rubber and friction tape should be painted with some good insulating compound. This tends to keep all acid fumes away from the wire. Acid fumes are not only liable to bring about a fire haz- ard, but are also irritating to employes. Thorough ventila- tion is therefore very important. 90 MODERN ELECTRICAL CONSTRUCTION. 11. Transformers. (For construction rules, see No. 62.) (See also Nos. 13, 13a, 36.) a. In central or sub-stations the transformers must be so placed that smoke from the burning out of the coils or the boiling over of the oil (where oil filled cases are used) could do no harm. If the insulation in a transformer breaks down, consid- erable heat is likely to be developed. This would cause a dense smoke, which might be mistaken for a fire and result in water being- thrown into the building, and a heavy loss there- by entailed. Moreover, with oil cooled transformers, especialls' if the cases are filled too full, the oil may become ignited and boil over, producing a very stubborn fire. b. In central or sub-stations casings of all transformer,' must be permanently and effectively grounded. Transformers used exclusively to supply current to switch- board instruments need not be grounded, provided they are thoroughly insulated. NOTICE— DO NOT FAIL TO SEE WHETHER ANY RULE OR ORDINANCE OF YOUR CITY CON- FLICTS WITH THESE RULES. Class B. OUTSIDE WORK. (Light, Power and Heat. For Signaling Systems, see Class E.) All Systems and Voltages. 12. Wires. a. Line wires must have an approved weatherproof or rubber insulating covering (see No. 44 and No. 41). That portion of the service wires between the main cut-out and switch and the first support from the cut-out or switch on outside of the building must have an approved rubber insulat- ing covering (see No. 41), but from the above mentioned support to the line may have an approved weatherproof in- sulating covering (see No. 44), if kept free from awnings, swinging signs, shutters, etc. By service wires are meant those wires which fenter the building. It is custom.ary to run the rubber-covered wire from the service switch and cut-out inside of building through the outer' walls, and to leave but a few feet of wire to which the line wires can later be spliced. This is illustrated in Figure 48, which shows how wires are run from pole to building. b. Must be so placed that moisture cannot form a cross connection between them, not less than a foot apart, and not 92 MODERN ELECTRICAL CONSTRUCTION. in contact with any substance other than their insulating sup- ports. Wooden blocks to which insulators are attached must be covered over their entire surface with at least two coats of waterproof paint. c. Must be at least 7 feet above the highest point of flat roofs, and at least one foot above the ridge of pitched roofs over which they pass or to which they are attached. Roof structures are frequently found which are too low or much too light for the work, or which have been carelessly put up. A structure which is to hold the wires a proper distance above the roof in all kinds of weather must not only be of sufficient height, but must be substantially constructed Of strong material. It is well to avoid fastening wires perpendicular above one another, as in winter icicles may form which extend from the Figure 48. top to the lower wire, and the moisture on these will often cause much trouble. The rule requires that wires be 7 feet above flat roofs, and roof structures must, therefore, be made high enough to allow for "sag." In moderately long runs 2 or 3 feet will be sufficient. For long runs, see following OUTSIDE WORK. 93 table, taken from construction rules of Commonwealth Elec- tric Company of Chicago : The tension on wires should be such that the sag of a span of 125 feet will not exceed the amounts shown. Temperature, F... 10 20 30 40 50 60 70 80 90 Sag, inches 6 8 8 10 10 12 12 14 14 This table will also be useful to consult when running wires over housetops to which they are not attached, as it shows the variation in "sag" due to different temperatures. Wires should be so run that even at the highest temperature they will still clear the buildings. Allowance should also be made for the gradual elongation of the wire to its own weight, giving way of supports or sleet that may at times weigh it down. d. Must be protected by dead insulated guard irons or wires from possibility of contact with other conducting wires or substances to which the current may leak. Special pre- cautions of this kind must be taken where sharp angles occur, or where any wires might possibly come in contact with elec- tric light or power wires. Crosses, when unavoidable, should he made as nearly at right angles as possible. These guard wires are run parallel to and above the lower set of wires. Their object is to prevent the upper crossing wires, should they break, from coming in contact with the lower. A separate set of cross arms must be placed on the lower poles or above the lower wires to which the guard wires must be fastened. In Figure 49 1 and 2 show break insulators that may be used to electrically disconnect guard e. Must be provided with petticoat insulators of glass or porcelain. Porcelain knobs or cleats and rubber hooks will not be approved. /. Must be so sphced or joined as to be both mechani- 94 MODERN ELECTRICAL CONSTRUCTION. cally and electrically secure without solder. The joints must then be soldered, to insure preservation, and covered with an insulation equal to that on the conductors. All joints must be soldered, unless made with some form of approved splicing device. This ruling- applies to joints and splices in all classes of wiring covered by these rules. Tn Figure 49 single and double petticoat insulators are shown. It is very often convenient to fasten such insulators upside down or horizontally, but this should never be done, as they will then fill with water or dirt and their insulating qualities be destroyed. g. Must, where they enter buildings, have drip loops out- side, and .the holes through which the conductors pass must be bushed with non-combustible, non-absorptive insulating tubes slanting upward toward the inside. For low potential systems the service wires may be brought into buildings through a single iron conduit. The conduit to be curved downward at its outer end and carefully sealed or equipped with an approved service-head to prevent the entrance of moisture. The outer end must be at least one H-..„jy Figure 49 foot from any woodwork and the inner end must extend to the service cut-out, and if a cabinet is required by the Code must enter the cabinet in a manner similar to that described in fine print note under No. 25 b. h. Electric light and power wires must not be placed on the same cross-arm with telegraph, telephone or similar wires, and when placed on the same pole with such wires the dis- OUTSIDE WORK. 95 tance between the two inside pins of each crossarm must not be less than twenty-six inches. i. The metalHc sheaths to cables must be permanently and effectively connected to "earth." The telephone of telegraph wires are sometimes placed above the power wires, and it very often becomes necessary for a lineman to pass .through the lower wires to get at the upper. Great care is necessary to avoid coming in contact with high tension power wires while handling the telephone wires. Poles should not be set more than 125 feet apart; 100 or 110 feet is good practice. For small wires poles with 6-inch tops are often used, but for heavier wires 7-inch tops are advisable. The tops of pole should be pointed, so as to shed water, and the whole pole be well painted. Steps should be placed so that the distance between any two steps on the same side is not over 36 inches ; these steps should all be the same distance apart, and should not extend nearer than 8 feet to the ground. All "gains" cut into poles should be painted before cross-arms are placed in them. Such places are more likely to hold moisture and rot than exposed parts. Wherever feed wires end or sharp angles occur, double cross- arms should be used, fastened on opposite sides of pole and bolted together. All bolts, lag screws, etc., should be galvanized. Poles should be set at least as far into the ground as shown in the following table: Length of pole. Depth in ground. 35 feet 5^ feet 40 " 6 45 " 6 50 " 6y2 " 55. '' 7 " 60 " 8 " 96 MODERN ELECTRICAL CONSTRUCTION. The holes should be large enough to admit of thorough tamping on all sides of bottom of hole. If the tamping at bottom of hole is not well done, the pole will always be shaky, no matter how much tamping may be done at the top. If the ground is soft, the pole may be set in cement, or short pieces of planking fastened to it at right angles underground. At the end of line or where sharp bends occur, strong gal- vanized guy cables fastened to poles six or eight feet long, buried underground, should be used. Trolley Wires. /. Must not be smaller than No. B. & S. gage copper or No. 4 B. & S. gage silicon bronze, and must readily stand the strain put upon them when in use. k. Mus.t have a double insulation from the ground. In wooden pole construction the pole will be considered as one insulation. /. Must be capable of being disconnected at the power plant, or of being divided into sections, so that, in case of fire on the railway route, the current may be shut off from the particular section and not interfere with the work of the firemen. This rule also applies to feeders. m. Must be safely protected against accidental contact where crossed by other conductors. Guard wires should be insulated from the ground and should be electrically disconnected in sections of not more than 300 feet in length. Ground Return Wires. n. For the diminution of electrolytic corrosion of under- ground metal work, ground return wires must be so arranged that the difference of potential between the grounded dynamo terminal and any point on the return circuit will not exceed twenty-five volts. It is sug-g-ested that the positive pole of the dynamo be connected to the trolley line, and that whenever pipes or other underground metal work are found to be electrically positive OUTSIDE WORK. 97 to the rails or surrounding: earth, that they be connected by conductors arranged so as to prevent as far as possible cur- rent flow from the pipes into the ground. 12 A. Constant-Potential Pole Lines, Over 5,000 Volts. (Overhead lines of this class unless properly arranged may increase the fire loss from the following causes: . _ Accidental crosses between such lines and low-potential lines may allow the high-voltage current to enter buildings over a large section of adjoining country. Moreover, such high voltage lines, if carried close to buildings, hamper .the work of firemen in case of fire in the building. The object of these rules is so to direct this class of construction that no increase in fire hazard will result, while a.t the same time care has been taken to avoid restrictions which would lin- reasonably impede progress in electrical development. It is fully understood that it is impossible to frame rules w^hich will cover all conceivable cases that may arise in con- struction work of such an extended and varied nature, and it is advised that the Inspection Department having jurisdiction be freely consulted as to any modification of the rules in par- ticular cases.) a. Every reasonable precaution must be takein in arrang- ing routes so as to avoid exposure to contact^ with other electric circuits. On existing lines, where there 'is, a liability to contact, the route should be changed by mutual agree- ment between the parties in interest wherever possible. . b. Stich lines should not approach other pole lines nearer than a distance equal to the height of the taller pole line, and such lines should not be on the skme poles with other wires, except that signaling wires used by the company operating the high-pressure system, and which do not enter property other than that owned or occupied by such com- pan}^ may be carried over the same poles. c. Where such lines must necessarily be carried nearer to other pole lines than is' specified in Section b above, or where i^ey — e- "r--oc-c-,-:i-- |^^ carried on the same poles with 98 MODERN ELECTRICAL CONSTRUCTION. other wires, extra precautions to reduce the liability of a breakdown to a minimum must be taken, such as the use of wires of ample mechanical strength, widely spaced cross- arms, short spans, double or extra heavy cross-arms, extra ? » >^ » I m Figure 50 heavy pins, insulators, and poles thoroughly supported. If carried on the same poles with other wires, the high-pressure wires must be carried at lea-st three feet above the other wires. d. Where such lines cross other lines, the poles of both lines must be of heavy and substantial construction. Wherever it is feasible, end-insulator guards should be placed on the cross-arms of the upper line. If the high-pres- OUTSIDE WORK. 99 sure wires cross below li.j other lines, the wires of the upper line should be deaa-enclecl at each end of the span to double-grooved, or to standard transposition insulators, and the line completed by loops. One of the following forms of construction must then be adopted : 1. The height and length of the cross-over span may be made such that the shortest distance between the lower cross-arms of the upper line and any wire of the lower line will be greater than the length of the cross-over span, so that a wire break- ing near one of the upper pins would not be long enough to reach any wire of .the lower line. The high-pressure wires should preferably be above the other wires. By reference to Fig. 50 it will be seen that the first plan of making cross-over is not very practical. In the lower left hand corner the vertical lines drawn alongside of the pole show the rate at which poles must be lengthened to comply wnth the rule when they are some distance from the pole to be crossed. If a line is to be crossed in this manner, economy and also good construction require that the poles be set close to the line to be crossed as shown at the right of the figure. The poles here are about twice the length of .the cross-arm apart. The wires between the two poles cannot touch the lower wires and the expense of the cross-over is only the setting of one pole and its cross-arms, etc. With the poles se.t as close as this there remains, however, the possibility of a wire in one of the adjacent spans breaking and, if strongly whipped about by the wind, being lashed against the lower wires. Guard wires can in a measure prevent such a wire coming in contact with the lower wire, but it is conceivable that the wire in question be broken . off at such a distance from the MODERN ELECTRICAL CONSTRUCTION. pole that it will swing over and lodge on top of the lower wires. If the cross-over poles are to be set farther apart to lessen this danger, .they must be increased two feet in height for every foot they are moved to one side. Figure 51 is a suggestion towards making crosses on a joint pole. It is simply a trough-like screen Ijuilt around the lower wires and set so that it must catch the upper wires when they break and confine them so that the wind cannot whip them out. A cross-over made on a joint pole in some such manner as this is probably the most satisfactory. Wires are abso- lutely prevented from coming together, and such a pole being braced by the wires in two ways would seem to be quite safe. When wires cross at rather an acute angle the Figure 51 screen mentioned stretched from pole to pole under the upper wires is probably the best safeguard. 2. A joint pole may be erected at the crossing point, high-pressure wires being supported on this pole at least three feet above the other wires. Mechan- ical guards or supports must then be provided, so that in case of the breaking of any upper wire it OUTSIDE WORK. 101 will be impossible for it to come into contact with any of the lower wires. Such liability of contact may be prevented by the use of suspension wires, similar to those em- ployed for suspending- aerial telephone cables, which will prevent the high-pressure wires from falling- in case they break. The suspension wires should be supported on hig-h potential insulators, should have ample mechanical streng-th, and should be carried over the hig-h-pressure wires for one span on each side of the joint pole, or where suspension wires are not desired guard wires may be carried above and below the lower wires for one span on each side of the joint pole, and so spread that a falling liigh-pressure wire would be held out of contact with the lower wires. Such g-uard wires should be supported on hi.?ii- potential insulators or should be g^rounded. When grounded, they must be of such size, and so con- nected and earthed, that they can surely carry to g-round any current which may be delivered by any of the high-pressure wires. Further, the construc- tion must be such that the g-uard wires will not be destroyed by any arcing at the point of contact likely to occur under the conditions existing-. 3. Whenever neither of the above methods is feasible a screen of wires should be interposed between the lines at the cross-over. This screen should be supported on high tension insulators or grounded and should be of such construction and strength as to prevent the upper wires from coming into contact with the lower ones. If the screen is g-rounded each wire of the screen must be of such size and so connected and earthed that it can surely carry to g-round any current which may be delivered by any of the hig-h pressure wires. Further, the construction must be such that the wires of screen will not be destroyed by any arcing at the point of contact likely to occur under the conditions existing. e. When it is necessary to carry such lines near buildings, they must be at such height and distance from the building as not to interfere with firemen in event of fire ; therefore, if within 25 feet of a building, they must be carried a.t a height not less than that of the front cornice, and the height must be greater than that of the cornice, as the wires come nearer MODERN ELECTRICAL CONSTRUCTION. to the building, in accordance with the following table : — Distance of wire Elevation of wire from building. above cornice of building. Feet. Feet. 25 20 2 15 4 10 6 5 8 21/2 9 It is evident that where the roof of the building: continue.s nearly in line with the walls, as in mansard roofs, the heiglit Figure 52. and distance of the line must be reckoned from some part of the roof instead of from the cornice. A graphic illustration of the rule concerning the placing of poles near buildings is given in Figure 52. The upper TKANS FORMERS. 103 group of figures and insulators shows the distance from the building and the corresponding height above high point of roof required with mansard roofs. Distance being measured from the roof. The lower groups show measurements taken from cornice line as will be proper with ordinary flat roofed buildings. 13. Transformers. (For construction rules, see No. 62.) (See also Nos. 11, 13A and 36.) Where transformers are to be connected to high-voltage circuits, it is necessary, in many cases, for best protection to life and property, that the secondary system be permanentlj'^ grounded, and provision should be made for it when the trans- formers are built. a. Must not be placed inside of any building, excepting central stations and sub-stations, unless by special permission of the Inspection Department having jurisdiction. An outside location is always preferable; first, because it keeps the high-voltage primary wires entirely out of the building and. second, for the reasons given in the note to No. 11 a. h. Must not be attached to the outside walls of buildings, unless separated therefrom by substantial supports. It is recommended that the transformers be not attached to frame buildings when any other location is practicabl'e. As a rule transformers are fastened .to buildings on horizontal bars of wood. This method is as satisfactory as any if the wood itself is securely enough fastened to the wall. The wooden supports of the transformer should be fastened to the wall either by suitable expansion bolts or bet- ter still by bolts passing entirely through the wall. In fast- ening transformers to poorly constructed walls where per- mission to go through the wall cannot be obtained, some ad- vantage can be gained by supporting the transformer sticks set vertically as shown in Figure 53. It must be borne in mind .that there is not only a downward strain on the sup- ports but also an outward tipping strain. Almost any wall 104 MODEIiN ELECTRICAL CONSTRUCTION. will Stand the downward strain but in a loosely constructed wall there may not be a good hold for the bolts and a heavy transformer may tear them out as indicated. If the trans- former is supported as indicated the supports may be dis- Figure 53. . tributed over a much larger wall area and a much greater leverage obtained against tipping strain than would be pos- sible with horizontally arranged timbers. The alternating current transformer consists of an iron core upon which wires of two distinct electrical circuits are wound. One of these is known as the primary circuit, and in it the high pressure currents coming direct from the dynamo circulate. The other is known as the secondary circuit, and in it the low pressure currents used inside of building circu- late. These .two circuits are wound generally one over the other, and are very close together. The pressure used in the primary coil is from 1,0C0 to 5,000 volts, while in the secondary it is reduced usually to 110 or 220. It quite frequently happens that the insulation between the TRANSFOKMEKS. 105 two windings breaks down and thus the high pressure is acci- dentally brought into buildings. Under such circumstances should any one touch any live part of the installation while touching also grounded parts of the building dea.th would very likely result. Also, should there be a weak spot in the insula- tion, it is quite likely the high pressure would pierce it at that point with a possible result of a fire. Many deaths and fires [B y U|//^K. @ S ^ 3 PHASE zjo r. Figure 54. have been caused in this way. If such lines are connected to ground the chances for harm are very much lessened, for the current will never take the path of high resistance through a man's body while a direct path through a low resistance wire is open to it. It must not be supposed that "grounding" one side of an electric light system is not often followed by serious conse- quences, for under such circumstances a ground coming on any other part of the system will cause a short circuit at once. 1C6 MODERN ELECTRICAL CONSTRUCTION. The grounding in these cases is to be looked upon as the lesser of two evils rather than as an advantage. With al- ternating currents, the chances of possible damage from grounding are much less than v^ith direct currents, because each transformer with its small group of lamps is a system by itself and no.t affected by grounds on other transformers. Thus a 5,000 light alternating current installation would con- sist of from 25 to 50 separate systems, each independent of defects on the rest, while in a continuous current installation a ground on the most remote branch circuit would in con- junction with a ground on the opposite pole of any other part of the system form a short circuit. Methods of grounding secondary wires of alternating cur- rent transformers are shown in Figure 54, taken fiom an instruction book issued by the Commonwealth Electric Com- pany of Chicago. In connection with 3-wire systems, grounding of the cen- tral wire can do little harm, because ordinarily the neutral wire seldom carries much current, and that current is apt to vary in direction so that the electrolytic effect will be on the whole quite negligible. There is, of course, the hazard brought about by the fact that a ground coming on one of the outside wires will imme- diately form a short-circuit in connection with the ground on the neutral. In connection with 3-wire sj^stems, however, it is of the greatest importance (as more fully explained further on) that the neutral wire remain intact, and it being thoroughly grounded at all available outside places will help to keep it so. ISA. Grounding Low-Potential Circuits. The grounding- of low-potential circuits under the follow- ing- regulations is only allowed when such circuits are so GROUNDING. 107 arrang-ed that under normal conditions of service there will be no passage of current over the g'round wire. Direct-Current 3-Wire System. a. Neutral wire may be grounded, and when grounded the following rules must be complied with : — 1. Must be grounded at the Central Station on a metal plate buried in coke beneath permanent moisture level, and also through all available underground water and gas-pipe systems. 2. In underground systems the neutral wire must also be grounded at each distributing box through the box. 3. In overhead systems the neutral wire must be grounded every 500 feet, as provided in Sections c to g. Inspection Departments having- jurisdiction may require grounding if they deem it necessary. Two-wire direct-current systems having no accessible neu- tral point are not to be g-rounded. Alternating-Current Secondary Systems. b. Transformer secondaries of dis.tributing systems should preferably be grounded, and when grounded, the following rules must be complied with : — 1. The grounding must be made at the neutral point, or wire, whenever a neutral point or wire is accessible. 2. When no neutral point or wire is accessible, one side of the secondary circuit may be grounded, pro- vided the maximum difiference of potential between the grounded point and any o.ther point in the cir- cuit does not exceed 250 volts. 3. The ground connection must be at the transformer or on the individual service as provided in sec- tions c to g, and when transformers feed systems with a neutral wire the neutral wire must also be grounded at least every 250 feet for overhead sys- tems and every 500 feet for underground systems. 108 MODEEX ELECTRICAL CONSTEUCTION. Inspection Departments having- jurisdiction may require grounding if they deem it necessary. Ground Connections. c. When the ground connection is inside of any building, or .the ground wire is inside of or attached to any building (except Central or Sub-stations) the ground wire must be of copper and have an approved rubber insulating covering National Electrical Code Standard, for from to 600 volts. (See No. 41.) d. The ground wire in direct-current 3-wire systems must not at Central Stations be smaller than the neutral wire and not smaller than No. 4 B. & S. gage elsewhere. The ground wire in alternating current systems must never be less than No. 4 B. & S. gage. On three-phase system, the ground wire must have a carrying capacity equal to that of any one of the three mains. e. The ground wire should, except for Central Stations and transformer sub-stations, be kept outside of buildings as far as practicable, but may be directly attached to the build- ing or pole by cleats or straps or on porcelain knobs. Staples must never be used. The wire must be carried in as nearly a straight line as practicable, avoiding kinks, coils and sharp bends, and must be pro,tected when exposed to mechanical injury. This protection can be secured by use of an approved moulding, and as a rule the ground wire on the outside of a building should be in moulding at all places where it is within seven feet from the ground. f. The ground connection for Central Stations, transform- er sub-stations, and banks of transformers must be made through metal plates buried in coke below permanent moisture level, and connection should also be made to all available underground piping systems including the lead sheath of un- derground cables. g. For individual transformers and building services the ground connection may be made as in Section /, or may be made to water piping systems running into the build- ings. This connection may be made by carrying the ground GROUND rLATES. 109 wire into the cellar and connecting on the street side of meters, main cocks, etc. Where it is necessar}' to run the ground wire through any part of a building it shall be protected by approved porcelain bushings through walls or partitions and shall be run in approved moulding, except that in basements it may be sup- ported on porcelain. In connecting- a ground wire to a piping- system, the wire should be sweated into a lug- attached to an approved clamp, and the clamp firmly bolted to the water pipe after all rust and scale have been removed; or be soldered into a brass plug and the plug forcibly screwed into a pipe-fitting-, or, where the pipes are cast iron, into a hole tapped into the pipe itself. For large stations, where connecting to underg-round pipes with bell and spig-ot joints, it is well to connect to several lengths, as the pipe joints may be of rather high resistance. Where ground plates are used, a No. .16 Stubbs' g-ag-e copper plate, about three by six feet in size, with about two feet of crushed coke or charcoal, about pea size, both under and over it, would make a ground of sufficient capacity for a moderate-sized station, and would probably answer for the ordinary substation or bank of transformers. For a large central station, a plate with considerably more area mig-ht be necessary, depending upon the other underground con- nections available. The ground wire should be riveted to the plate in a number of places, and soldered for its whole leng-th. Perhaps even better than a copper plate is a cast- iron plate with projecting forks, the idea of the fork being to distribute the connection to the ground over a fairly broad area, and to give a large surface contact. The ground wire can probably best be connected to such a cast-iron plate by soldering it into brass plugrs screwed into holes tapped in the plate. In all cases, the joint between the plate and the ground wire should be thoroughly protected ag-ainst corrosion by painting- it with waterproof paint or some equivalent. NOTE.— DO NOT FAIL TO SEE WHETHER ANY RULE OR ORDINANCE OF YOUR CITY CONFLICTS WITH THESE RULES. Class C. INSIDE WORK. (Light, Pozver and Heat. For Signaling Systems, see Class E.) All Systems and Voltages. GENERAL RULES. 14. Wires. {For special rules, see A^os. i6, i8, 24, J5, jc? and jp.) a. Must not be of smaller size than No. 14 B. & S. gage, except as allowed under Nos. 24 v and 45 h. The exceptions being wires used inside of fixtures and flexible cord ased to suspend individual electric lights. For general purposes a wire smaller than No. 14 is too easily broken, either through a sharp kink or by drawing too tight with tie wires. To avoid trouble from kinks or sharp bends, wires smaller than 14 should preferably be stranded. h. Tie wires must have an insulation equal to tha.t of the conductors they confine. The use of some form of confining knob or insulator which will dispense with tie wires is recommended. This is considered necessary, because very often the tie wire cuts through the insulation of the wire it confines, and if the tie wire should come in contact with other than its msu- INSIDE WOKK. lating support, there would still be good insulation. In Figu';e 55, (1) and (2) illustrate the method of tying usually em- ployed with small wires on insulators ; (4) shows a method Figure employed with larger wires. This is also especially useful, because slack can be taken up if the tie wire is arranged to draw the main wire about half way around the insulator; (6) MODERN ELECTRICAL CONSTRUCTION. INSIDE WORK. 113 sliows a knot tied into the wire, as is usual where the end of the wire connects into cut-outs or switches. At (5) insula- tors are arranged to hold large ^wires. It is not advisable to tie large wires to insulators, as the weight of the wir(b will soon cause it to cut through the insulation. Cleats, such as shown at (8) and (9), are preferable. c. Must be so spliced or joined as to be both mechanically and electrically secure without solder. The joints must then be soldered to insure preservation, and covered with an insu- lation equal to that on the conductors. Stranded wires must be soldered before being fastened under clamps or binding screws, and whether stranded or solid w^hen they have a conductivity greater than that of No. 8 B. & S. gage they must be soldered into lugs ^^or all terminal connections. All joints must be soldered unless made with some form of appyoved splicing device. This ruling- applies to joints and splices in all classes of wiring covered by these rules. On the left at the upper part of Fig. 56 is shown the well- known Western Union joint. Before joining wires they should be thoroughly cleaned by scraping wi.th the back of a knife or sand or emery paper. The insulation should be removed, as indicated at h; if it is cut into as at a^ it is very likely that the wire will be "nicked" and will be likely to break at that point. It is also more difficult to tape a joint properly if the rubber has been cut in this way than it is with the rubber cut as at b. After the joint has been made it is covered with soldering fluid, a formula for which is given below. In lieu of this there are soldering sticks and salts, already prepared, on the market. The following formula for soldering fluid is suggested : — Saturated solution of zinc chloride 5 parts Alcohol . . 4 parts Glycerine 1 part The joint having been thoroughly covered with one of 114 MODERN ELECTRICAL CONSTRUCTION. these preparations is next heated with a gasoline or alcohol torch and a small piece of solder allowed to melt on it near the center. It is well to avoid heating too much at the ciids of the joint, as it weakens the wire. After the joint is partly cooled wipe off all moisture and cover with layers of rubber tape, enough, at least, so that it is equal in thickness lo the rubber insulation on the wire used, as shown at a and b. If the rubber tape is put on before the wire has entirely cooled the remaining heat will assist in vulcanizing the rubber. This rubber tape is then covered with friction tape to keep it in place. Before taping joints the outer braid of the wire should be carefully skinned back. If any of the cotton threads of which it consists w^ere to be left in contact with the bare wire, they would, when moist, form a leak, which might prove trou- blesome. If joints are exposed to the weather it will be well to paint them over with some insulating paint to keep :he friction tape in place, as it will otherwise soon work loose when it becomes dry. At c and d "tap" joints are shown. The method shown at d is preferable, because .the wire cannot easily work loose. The method of joining shown at e is useful when, for instance, two wires, each of which is fastened to an insulator, are to be joined. The wires can be drawn very tight in this way. This sort of joint is very common in fixture work, and should be finished off as at /. Twin wires other than flexible cord are allowed only in metal conduits, and joints in them should be made only within the junction boxes. When joints in conduit are unavoidable, twin wires should be joined as at g, so that the joints are not opposite each other. Joints in flexible cord should be avoided as much as possible. In splicing stranded wires it is customary to remove some of .the center strands to avoid making a very bulky splice. All INSIDE WORK. 115 stranded wires must be soldered where fastened under binding screws ; this refers also to flexible cord nsed in sockets. The best way to solder the ends of cords is to dip them in melted solder; a blow torch will easily c»verheat small wires and leave them brittle. Figure 57 shows lead covered wire spliced and laped. In handling lead covered wire great care must be exercised (especially with paper insulated) that it be not bruised and the lead not punctured. The lead covering is of use only as a protection against water; if it admits the least bit of moisture it is worse than useless. The ends of lead covered wires should always be kept sealed until ready for use ; in damp places the paper insulation may absorb moisture, which will ground the wire on .the lead. When installed the ends should always be sealed against moisture. Lead covered wires should never be used where there is a liability of nails being driven into them. Joints in lead covered wires are made just as in ordinary wires. Extreme care is necessary that no moisture be left on Figure 57. the wire when it is taped or covered up. Before the wire is joined a sleeve (Figure 57) is slipped over one of the wires. After the joint has been made and taped, this sleeve is placed so as to cover it, and the ends split and arranged to fit close against the lead on the wires. That part of the lead which must be soldered to make the joint watertight is scraped until it is perfectly bright and then coated with tallow candle grease. It can then be soldered with an iron, or melted solder can be 116 MODEKN ELECTRICAL CONSTRUCTION. poured on it and wiped around it, as plumbers do. If a soldering iron is used it must not be too hot and not allowed to remain in one place too long, as the lead itself melts at nearly the same temperature as the solder. An inexperienced workman may burn more holes into the lead than he closes. If a neat job is desired, that part of the lead which is to be kept free of solder is covered with lampblack and glue, or ordinary paper hanger's paste, or a m-ixture of flour and water boiled, so as to prevent the solder from taking on it. d. Must be separated from contact with walls, floors, timbers or partitions through which they may pass by non- combustible, non-absorptive insulating tubes, such as glass or porcelain, except as provided in No. 24 u. Bushing-s must be long- enough to bush the entire length of the hole in one continuous piece or else the hole must _IL Figure 58 first be bushed by a continuous waterproof tube. This tube may be a conductor, such as iron pipe, but in that case an insulating bushing must be pushed into each end of it, ex- tending far enough to l//. 'fn rf/ ////// /^^ Figure 92. (when required), if carrying alternating current must, or if direct current, may be placed within the same pipe. In damp places! the wooden boxing may be preferable be- cause of the precautions which would be necessary to secure proper insulation if the pipe were used. With this exception, however, iron piping is considered preferable to the wooden LOW POTENTIAL SYSTEMS. 159 boxing, and its use is strongly urged. It in especially suit- able for the protection of wires near belts, pulleys, etc. /. When run in unfinished attics, will be considered as concealed, and when run in close proximity to water tanks or pipes will be considered as exposed to moisture. In unfinished attics wires are considered as exposed to mechanical injury, and must not be run on knobs on upper edge of joists. Figure 92 illustrates the meaning of the rule in regard to wires run along low ceilings. Figure 93 gives the dimensions necessary for boxing wires on side walls. At the right, the side wall protection consists of conduit; a junction -box with the lower side knocked out is used to enclose bushings. When the cover is screwed on the wires are completely enclosed. SPECIAL RULES. For Open Work. In dry places. g. Must have an approved rubber, slow-burning weather- proof, or slow-burning insulation (see Nos. 41, 42 and 43). A slow-burning covering, that is, one that will not carry fire, is considered good enough where the wires are entirely on insulating supports. Its main object is to prevent the copper conductors from coming accidentally into contact with each other or anything else. h. Must be rigidly supported on non-combustible, non- absorptive insulators, which will separate the wires from each other and from .the surface wired over in accordance with the following table : Voltage. Distance from Distance between Surface. Wires. to 300 1/2 inch 21/^ inch 300 to 550 1 inch 4 inch Rigid supporting requires, under ordinary conditions, where vV'iring along' flat surfaces, supports at least every four and one-half feet. If the wires are liable to be disturbed, the dis- tance between supports should be shortened. In buildings of MODERN ELECTRICAL CONSTRUCTION. mill construction, mains of No. 8 B. & S. gage wire or over, where not liable to be disturbed, may be separated about six inches, and run from timber to timber, not breaking around, and may be supported at each timber only. This rule will not be interpreted to forbid the placing of the neutral of an Edison three-wire system in the center of a Figure 93. three-wire cleat where the difference of potential between the outside wires is not over 300 volts, provided the outside wires are separated two and one-half inches. Figure 94 shows different methods of running wires in buildings of mill construction. If the method shown at a is J used, a few insulators should be placed here and there and the! wires tied to them to prevent sagging. The arrangements' shown at b and c are suitable for small wires on high ceil- ings. The methods shown at d and e are sometimes used where LOW POTENTIAL SYSTEMS. there is no danger of interference. With long spans, supports as shown at / may be used. TBT Figure 94. In damp places, or huiMings specially subject to moisture or to acid or other fumes liable to injure the wires or their insulation. i. Must have an approved insulating covering. For protection against water, rubber insulation must be used. For protection against corrosive vapors, either weather- proof or rubber insulation must be used. (See Nos. 41 and 44.) j. Must be rigidly supported on non-combustible, non-ab- sorptive insulators, which separate the wire at leas.t one inch from the surface wired over, and must be kept apart at least two and one-half inches for voltages up to 300 and four inches for higher voltages. Rigid supporting requires, under ordinary conditions, where wiring over flat surfaces, supports at least every four and one- half feet. If the wires are liable to be disturbed, the distance between supports should be shortened. In buildings of mill construction, mains of No. 8 B. & S. gage wire or over, where not liable to be disturbed, may be separated about six inches, and run from timber to timber, not breaking around, and may be supported at each timber only. In damp places the wires are often run on the under side of an inverted trough as shown in Figure 95. The main point of usefulness of such a .trough lies in the fact that it prevents drippings from wetting the wires and insulators. Condensa- tion will, however, keep insulators and wires wet neverthe- less. The trough, to be useful, should be put together with many 1G2 MODEKN KLECTRICAL CONSTRUCTION. screws, the butting edges of the boards -having been first painted with a waterproof paint, with which, when finished, the whole trough is also painted inside and out. Notwithstanding the rule given above, it would seem far better where practicable to use petticoat insulators and keep them much farther apart, even if, in order to do so, a larger wire would be required. Each insulator, when wet, allows some current to leak over its surface and, therefore, the fewer we have the better so long as there is no danger of breaking wires. If splices arc necessary in wet places they should be made quite a distance from insulators , the insula- tion of a splice being always weaker than that of the unbroken wire. Care should also be taken that the insulation of wires be not damaged through tying. Weather-proof sockets are required by the rule and are Figure 95. best in such places when not subject to much handling. As these are, however, easily broken, brass shell sockets are of.ten used. These are thoroughly covered with tape and compound so as to exclude all moisture and are very durable. LOW POTENTIAL SYSTEMS. For Moulding Work (Wooden and Metal). {For constniction rules see No. 50. See also No. 25 A.) k. Must have an approved rubber insulating covering. (For wooden moulding see .No. 41, for metal moulding see No. 47.) /. Must never be placed in either metal or wooden mould- ing in concealed or damp places or where the difference of potential between any two wires in the same moulding is over 300 voLts. Metal mouldings must not be used for circuits requiring more than 660 watts of energy. As a rule, wooden moulding- should not be placed directly against a brick wall, as the wall is likely to "sweat" and thus introduce moisture back of the moulding-. m. Must for alternating current systems if in metal moulding have the two or more wires of a circuit installed in the same moulding. It is advised that this be done for direct current systems also, so that they* may be chang-ed to alternating- systems at any time, induction troubles preventing such a change if the wires are in separate mouldings. Figure 96 shows the dimensions of approved moulding. Figure 96. Figure 97. Figure 97 shows the proper method of making a tap joint moulding. This method brings the capping between the two in mou 164 MODEBN ELECTIIICAL CONSTRUCTION. wires of opposite polarity. Wires should never be crossed be- low the capping. If the exposed wire in Figure 97 is objec- tionable, part of the back of moulding may be cut out, or the wall back of the moulding may be gouged out as shown in Fig- ure 98. This method must, however, never be used with other than walls or partitions of hardwood. Figure 99 shows proper method of tapping flexible cord to Fig. Figure 99. wires in moulding. The vv^hole cord should never be taken out of one hole in capping. There is always some chance of abrasion and joints are often poorly covered, so that there is always more likelihood of short circuits at this point. Figure 100 shows how moulding should be fastened to tile ceiling. When toggle bolts are used, the nut should always be put on outside of capping (unless a very small one is used, or more than ordinary care is exercised). Many wiremen are careless and cut away the middle tongue too much, giving the nut a chance to work itself diagonally across it, so as to come in contact with both wires and, in time perhaps, cause short circuits. Although toggle bolts are mostly used, screws have been successfully used in tile. It is only necessary to first drill a hole of just the proper size for the screw to be used. A very rough, quick way of making a square turn with LOW rOTENTIAL SYSTEMS. moulding is shown in Figure 101. One piece is cut entirely off along the line a; the pieces are then joined as shown and Figure 101. Figure 102. the capping hides the botch work. Such work will not be passed by inspectors if no.ticed. The proper way of fitting moulding is shown in Figure 102. Figure 103 shows methods of running around corners. The saw cuts, a, b, c, etc., should be made with a fine saw and for short bends require to be close together. Bending is Figure 103. facilitated by wetting the moulding, and if, before the mould- ing is put in place, the saw cuts are filled with glue, it v/ill greatly add .to the durability of the job. Screws or nails used in fastening the capping should pass through the mould- ing into the wall to get a firm hold. I 166 MODEEN ELECTKICAL CONSTRUCTION. For Conduit Work. n. Must have an approved rubber insulating covering (see No. 47). 0. Must not be drawn in until all mechanical work on the building has been, as far as possible, completed. Conductors in vertical conduit risers must be supported within the conduit system in accordance with the following table :— No. 14 to every 100 feet. No. 00 to 0000 every 80 feet. 0000 to 350,000 C. M. every 60 feet. 350,000 C. M. to 500,000 C. M. every 50 feet. 500,000 C. M. to 750,000 C. M. every 40 feet. 750,000 C. M. every 35 feet. A turn of 90 degrees in the conduit system will constitute a satisfactory support, as per above table. The following methods of supporting cables are recom- mended : — ■ 1. Junction boxes may be inserted in the conduit system at the required intervals, in which insulating sup- ports of approved type must be installed and se- cured in a satisfactory manner so as to withstand the weight of the conductors attached thereto, the boxes to be provided with proper covers. 2. -Cables may be supported in approved junction boxes on two or more insulating supports so placed that the conductors will be deflected at an angle of not less than 90 degrees and carried a distance of not less than twice .the diameter of the cable from its vertical position. Cables so suspended may be additionally secured to these insulators by tie wires. Other methods, if used, must be approved by the Inspec- tion Department having jurisdiction. Figure 104 shows different methods employed to fasten LOW I'OTEXTIAL .SV:;TEMS. 1C7 wires in vertical runs in conduits. In the upper left-hand figure insulators are used, reinforced by metal straps so ar- ranged that they will prevent the insulators from being pulled off sideways. The method shown in the lower figure is some- a ■■ 1 ^ r ci^ u ®5** /§> r x^ ^'^.y f-A fef ( ' 1 "P= -T- ' 1 — r % i Oporcelain[oj 1 1 1 — i 1 — ' Figure 104. times used with cables so heavy that the rubber insulation will not stand the strain of supporting them. The figure shows a clamp made of copper so that it can be soldered to the bare wires of the cable. This clamp is mounted on slate so as to furnish the insulation necessary for the cable. p. Must, for alternating systems, have the two or more wires of a circuit drawn in the same conduit. It ia advised that this be done for direct-current systems 168 MODEEN ELECTRICAL CONSTRUCTION. also, SO that they may be changed to alternating systems at any time, induction troubles preventing such a change if the wires are in separate conduits. The same conduit must never contain circuits of different isystems, but may contain two or more circuits of tlie same system. If a single wire carrying alternating currents of electricity were run in iron pipe there would be a very large drop in voltage. This drop is due to the fact that all currents while changing in strength generate a counter E. M. F. in their sur- roundings. This is particularly strong when the wires are sur- rounded by, or very close to, iron. If both wires are run in the same pipe the current in one wire neutralizes that of the other and there is no trouble. For Concealed "Knob and Tube" Work. q. Must have an approved rubber insulating covering (see No. 41). ■ _ r. Must be rigidly supported on non-combustible, non-ab- sorptive insulators which separate the wire at least one inch from the surface wired over. Should preferably be run singly on separate timbers, or studdings, and must be kept at least five inches apart. Must be separated from contact with the walls, floor timbers and partitions through which they may pass by non-combustible, non-absorptive insulating tubes, such as glass or porcelain. Rigid supporting requires, under ordinary conditions, where wiring along flat surfaces, supports at least every four and one-half feet. If the wires are liable to be disturbed, tlie distance between supports should be shortened. At distributing centers, outlets or switches where space is limited and the five-inch separation cannot be maintained, each wire must be separately encased in a continuous length of approved flexible tubing. Wires passing through timbers at the bottom of plastered partitions must? be protected by an additional tube extending at least four inches above the timber. .y. When, in a concealed knob and tube system, it is im- practicable to place the whole of a circuit on non-combustible supports of glass or porcelain, that portion of the circuit which cannot be so supported must be installed with approved LOW POTENTIAL SYSTEMS. 169 metal conduit, or approved armored cable (see No. 24 0. ex- cept that if the difference of potential between the wires is not over 300 volts, and if the wires are not exposed to mois- ture, they may be fished if separately encased in approved flexible tubing, extending in continuous lengths from porce- lain support to porcelain support, from porcelain support to outlet, or from outlet to outlet. An illustration of wiring on the "loop" system is shown in Figure 105. This system makes it unnecessary .to have any concealed joints or splices. The amount of wire required is somewhat in excess of that required for tap systems, but this is often balanced by a saving in labor. Sometimes, however, the labor is also in excess of that required for tap systems. 170 MODEr.N ELECTRICAL COXSTKUCTIOX. The main advantage of the system is that all joints and splices are always accessible. The figure also shows mixed "knob and tube" work and "conduit" work. Along the walls behind the furring strips there is seldom sufficient space to admit of knob and tube work and conduit must be used. t. Mixed concealed knob and tube work is provided for in No. 24 s, must comply with requirements of No. 24 n to p, and No. 25, when conduit is used, and with requirements of No. 24 A, when armored cable is used. u. Must at all outlets, except where conduit is used, be protected by approved flexible insulating tubing, extending in continuous lengths from the last porcelain support to at kast one inch beyond the outlet. In the case of combination fix- tures the tubes must extend at least flush with outer end of gas cap. It is recommended, but not required, that approved outlet boxes or plates be installed at all outlets in concealed "knob and tube" work, the wires to be protected by approved flexible insulating tubing, extending' in continuous lengths from the last porcelain support into the box. Figure 106 is drawn to illustrate "fish work." Fish work is used in finished buildings, mostly, and is often very tedious and expensive. Hours are sometimes spent before wires can be brought through and often the effort is an entire failure. In combination work, as shown in Figure 91, there is usually little trouble, as there is the whole spnn between joists to run wires in. An eft'ort to fish a.t right angles to the joists (when there are si-rips under joists) is more diflicidt, but often suc- cessful if the distance is not too great When there are two men the usual method of- fishing is: One man takes a wire sufficiently long to reach from one open- ing .to the other, and, after bending a small hook on one end in such a way that it will not catch easily on obstructions, pushes this end into one opening and, by twisting and working backward and forward, gradually forces it toward the oth.er LOW POTENTIAL SYSTEMS. 171 opening. At this opening his helper is stationed with a short wire, also provided with a hook, with which he must seek to catch the other wire when it comes near his opening. When the two wires come in contact, the larger one is drawn out and the conducting wires (encased in approved flexible tubing) are fastened to it and drawn through. The tubing should always be put on the wires before drawing in. If it is put on ■,ijW^^>-i;g>,.yy-j.bwt,v'^wiHnu!gn:T!7i ^-. ^ -W. ^ i'^^Aii.iKi ■ ir^i..-'>J ! >)^-^i-'J' ■ h^-■;'.W . ,^^^'ill not be approved if installed over spe- 194 MODERN ELECTRICAL CONSTRUCTION cially inflammable stuff, or where exposed to flyings of com- bustible material. Waterproof sockets are constructed entirely of porcelain and are not provided with keys, therefore the circuits .to which they are connected must be controlled by switches. As a gen- eral rule these sockets are furnished with a short piece of Figure 115. stranded, rubber-covered wire extending through sealed holes in the top of the socket and the supporting wires are soldered to them. The method of suspending waterproof sockets varies with the conditions. Ordinarily, stranded rubber-covered wires of the proper length are suspended from single cleats as shown at b, in Figure 115, or, if the line knobs are large enough, the stranded wire may be supported from them. If the lamp is to be suspended only a short distance from the ceiling, where it will not be liable to be disturbed, it may be I LOW POTENTIAL SYSTEMS. 195 hung from two ordinary inch porcelain knobs, as shown in Figure 95. If cleats are used in a damp place for supporting the drop a half cleat must be provided back of the supporting cleat to give a one-inch separation, as required for wires in wet places. 28. Flexible Cord. a. Must have an approved insulation and covering (see No. 45). b. Must not be used where the difference of potential between the two wires is over 300 volts. The above rule does not apply to the grounded circuits In street railway property. c. Must not be used as a support for clusters, d. Must not be used except for pendants, wiring of fix- tures, portable lamps or motors, and portable heating ap- paratus. The practice of making the pendants unnecessarily long and then looping- them up with cord adjusters is strongly advised against. It offers a temptation to carry about lamps which are intended to hang freely in the air, and the cord adjusters wear off the insulation very rapidly. For all portable work, including those pendants which are liable to be moved about sufficiently to come in contact with surrounding objects, flexible wires and cables especially de- signed to withstand this severe service are on the market, and should be used. (See No. 45 f.) The standard socket is threaded for one-eighth-inch pipe, and if it is properly bushed the reinforced flexible cord will not go into it, but this style of cord may be used with sockets threaded for three-eighths-inch pipe, and provided with sub- stantial insulating bushings. The cable to be supported inde- pendently of the overhead circuit by a single cleat, and the two conductors then separated and soldered to the overhead wires. The bulb of an incandescent lamp frequently becomes hot enough to ignite paper, cotton and similar readily ignitible materials, and in order to prevent it from coming in contact with such materials, as well as to protect it from breakage, every portable lamp should be surrounded with a substantial wire guard. Cord adjusters should never be used where their use can be avoided and where they are installed should only be placed 196 MODERN ELECTRICAL CONSTRUCTION. on lamps which will seldom need adjusting. The indis- criminate use of cord adjusters cannot be too strongly con- demned, as the constant rubbing soon destroys the insulation. At c, Figure 115, shows a brass socket threaded for ^-inch pipe, and which is designed to be used with portable cord. Care should be taken in making up these sockets to see that the knot under the head of .the socket has a good bearing surface so that it will not pull through the larger bushing, these portables being very apt to be jerked about. A lamp guard to be of any value should be so constructed that the bulb of .the lamp cannot come in contact with any- thing outside of the lamp guard; it should also protect the lamp from any sudden jar. The design of the guard should be such that it can be firmly attached to the socket so it will no.t work loose and come in contact with the live butt of the lamp or projecting threaded portion of the socket. e. Must not be used in show windows except when pro- vided with an approved metal armor. The great number of fires which have been caused by the use of flexible cord in show windows is sufficient argument against its use. /. Must be protected by insulating bushings where .the cord enters the socket. g. Must be so suspended that the entire weight of the socket and lamp will be borne by some approved device under the bushing in the socket, and above the point where .the cord comes through the ceiling block or rosette, in order that the strain may be taken from the joints and binding screws. This is usually accomplished by knots in the cord Inside the socket and rosette. Special ceiling blocks or rosettes which facilitate the fastening of cords are on the market and should be used. In fastening the cord to sockets the end of the cord should be soldered. This does away with the liability of stray strands LOW POTENTIAL SYSTEMS. 197 short circuiting on the shell of the socket and also affords a better and stronger contact under the binding screws. This soldering is best done by dipping the ends of the cord in melted solder. If a blow torch is used the small wires are very easily overheated and the soldering may do more harm than good. It is also well to tape .the ends of cords, leaving only just enough bare metal to go under the binding screws ; the tape will hold the end of the braid and will confine any ends of wires which do not happen to come under the binding screws. 29. Arc Lamps on Constant-Potential Circuits. a. Must have a cut-out (see No. 17 a) for each lamp or each series of lamps. The branch conductors should have a carrying- capacity about 50 per cent in excess of the normal current required by the lamp to provide for heavy current required when lamp is started or when carbons become stuck without overfusing the wires. Figure 116 a.t the left gives a diagram of a constant poten- tial arc circuit as generally used at present for enclosed arc Figure 116. lamps. Each arc lamp of this kind requires a pressure of 110 volts. A steadying resistance, R, is always placed in series with constant potential lamps, its object being to keep down the current while the lamp feeds. During .the short time that 198 MODERN ELECTRICAL CONSTRUCTION. the two carbons are together, the resistance of the lamp is so low that an enormous amount of current would flow were it not for this resistance. With most lamps this resistance is now installed in the hood. Since the rule requires a carrying capacity about 50 per cent in excess of the normal current for branch conductors, it would be well to provide this also for mains in such cases where groups of arc lamps are likely to be controlled by one switch and used together. Figure 116 at the right shows a diagram of wiring for open arc lamps. Two lamps are usually run in series on 110 volts together with a steadying pressure. An open arc does not work well with a pressure higher than about 45 volts. b. Must only be furnished with such resistance or regula- tors as are enclosed in non-combustible material, such resist- ances being treated as sources of heat. Incandescent lamps must not be used for this purpose. c. Must be supplied with globes and protected by spark arresters and wire netting around the globe, as in the case of series arc lamps (see Nos. 19 and 58). Outside arc lamps must be suspended at least eight feet above sidewalks. Inside arc lamps must be placed out of reach or suitably protected. d. Lamps when arranged to be raised and lowered, either for carboning or other purposes, shall be connected up with stranded conductors from the last point of support to the lamp, when such conductor is larger than No. 14 B. & S. gage. 30. Economy Coils. a. Economy and compensator coils for arc lamps must be mounted on non-combustible, non-absorptive insulating sup- ports, such as glass or porcelain, allowing an air space of at least one inch between frame and support, and muct in gen- eral be treated as sources of heat. 31. Decorative Lighting Systems. a. Special permission may be given in writing by the LOW POTENTIAL SYSTEMS. 199 Inspection Department having jurisdiction for the temporary installation of approved Systems of Decorative Lighting, pro- vided the difference of potential between the wires of any circuit shall not be over 150 volts and also provided that no group of lamps requiring more than 1,320 watts shall be de- pendent on one cut-out. No "System of Decora,tive Lighting" to be allowed under this rule which is not listed in the Supplement to the National Electrical Code containing list of approved fittings. 31 A. Theater Wiring. {For rules governing- Moving Picture Machines see No. 65 A.) All wiring apparatus, etc., not specifically covered by special rules herein given must conform to the Standard Rules and Requirements of the National Electrical Code. In so far as these Rules and Requirements are concerned, the term "theater" shall mean a huilding or part of a build- ing in which it is designed to make a presentation of dramatic, operatic or other performances or shows for the entertain- ment of spectators which is capable of seating at least four hundred persons, and which has a stage for such perform- ances that can be used for scenery and other stage appliances. A. Services. 1. Where source of supply is outside of building there must be at least two separate and distinct services where practicable, fed from separate street mains, one service to be of sufficient capacity to supply current for the entire equip- ment of theater, while the other service mus.t be at least of sufficient capacity to supply current for all emergency lights. By "emergency lights" are meant exit lights and all lights in lobbies, stairways, corridors and other portions of theater to which the public have access which are normally kept lighted during the performance. 2. Where source of supply is an isolated plant within same building, an auxiliary service of at least sufficient ca- pacity to supply all emergency lights must be installed from some outside source, or a suitable storage battery within 200 MODERN ELECTRICAL CONSTRUCTION. the premises may be considered the equivalent of such serv- ice. The spirit of this rule requires that the "emergency" light- 1 Light Circuits M/^)N ForHovj se and Stage. Figure 117. ing system be kept entirely separate and distinct from the general lighting system. The emergency lighting system is LOW POTENTIAL SYSTEMS. 201 designed to provide illumination sufficient for the audience to get from the auditorium to the outside of the building under any and all conditions liable to exist, even where the general illuminating system has been rendered useless. It is, there- fore, of the utmost importance that the emergency system ;be made as reliable as is possible to the end that under no con- dition liable to exist will these lights be out of service. Fig- ure 117 shows how this rule and also e-4 may be complied with. The emergency circuit should if possible be taken from mains that have no connection whatever with those supplying the auditorium and stage lights. The emergency mains must lead to the lobby and are not allowed to have any fuses except those at the street and those finally pro- tecting the branch circuits. Under certain interpretation of this rule it is permissible to connect the two systems as Figure 118. shown by dotted lines. This is, however, bad practice, as the switch may be unintentionally left as shown in the cut and thus when the main fuse blows all of the lights will be 202 MODERN ELECTEICAL CONSTRUCTION. out. In many cases this arrangement will be very costly, as often lobby and theater mains do not run close together. As there is to be only one fuse between street and cut-out box, the mains to lobby will have to be of the same size as the house mains. It will be a good plan to arrange the house mains as shown in Figure 118. The double throw switch is provided 1 merely to enable a quick re-illumination to take place in case one of the fuses were to blow. The switch is located at the LOW POTENTIAL SYSTEMS. 203 electrician's station and it is but necessary for him to throw the switch to the other side to light up the house again. In order to be certain that the fuse in the street will not blow, the wires between street and switch may be made sev- eral sizes heavier than required and fuse accordingly. Under such circumstances it is extremely unlikely that any but the fuse at the electrician's station will blow. b. Stage. 1. All permanent construction on stage side of pro- scenium wall must be approved conduit, with the exception of border and switchboard wiring. 2 Szvitchhoards. — Must be made of non-combustible, non-absorptive material, and where accessible from stage level must be protected by an approved guard-rail to prevent accidental contact with live parts on the board. The switchboard of necessity being close to the stage proper is generally in such a position that persons leaving the stage pass directly in front of it. As the costumes worn by actors are very often made up of tinsel or other conduct- Figure 120. ing material, and as various metal trappings are carried, it is essential that the guard rail be of such design as to pre- 204 MODERN ELECTRICAL CONSTRUCTION. vent these materials from coming in contact with the live parts of the board. Where the guard rail is placed close to the board it is often advisable to provide a screen between the guard rail and the floor. 3. Footlights. a. Must be wired in approved conduit, each lamp recep- tacle being enclosed within an approved outlet box, the whole to be enclosed in a steel trough, metal to be of a thickness not less than No. 20 gage, or each lamp receptacle may be mounted on or in an iron or steel box so constructed as to enclose all the wires and live parts of receptacles. h. Must be so wired that no set of lamps requiring more than 1,320 watts will be dependent on one cut-out. Figure 119 shows a number of forms in which footlight troughs are made up. These troughs are constructed of No. 20 Stubbs gage iron or steel, the receptacles being attached to the upper section as shown in Figure 120. The completed footlight strip is shown in Figure 121. These Figure 121. strips are combined in various ways to make up the foot- light proper, their arrangement depending on the lighting effect desired. A common arrangement is shown in Figure 122, where two separate strips are used, one elevated above the other in order that the light from the back row of lamps will not be obstructed by the lamps in the front row. When footlights are installed in this manner more light is ob- tained when the clear lamps are placed in the front row, as only a small part of the light emitted from the colored lamps LOW rOTENTIAL SYSTEMS. ^US will be absorbed by passing through the clear globes, while, with the reverse arrangement, where the colored lamps are placed in the front row, a considerable amount of light would be absorbed by the light from the clear lamps passing through the colored glass. Owing to the fact that the foot- lights are generally placed in troughs cut in the stage floor, thus bringing the lamps below the level of the stage floor, the placing of the white lamps in the lower row would not Figure 122. allow sufficient light to illuminate the back part of the stage, and for this reason where footlights are placed as shown in the figure it is the usual practice to place the white lights in the upper row. Where all the lamps, both white and colored, are placed vO-Q-a^^-D-^a- Figure 123. in one row, a reflector of the design shown in Figure 123 will materially increase the useful light. Receptacles used in footlight construction must be of ap- proved design and where the receptacle is fastened to the 206 MODERN ELECTRICAL CONSTRUCTION. metal work with porcelain or metal threaded rings the re- ceptacle must be so designed that it cannot be turned by the insertion or extraction of the lamp. This is generally accomplished by means of notches or projections on the porcelain of the receptacle and the metal should always be stamped to fit these parts. Double braid, rubber covered wire must be used, and, with clip sockets, the wire must be soldered to the clip, in addition to being fastened by the binding screws. If the porcelain of the receptacle does not provide proper protec- tion all exposed contacts, including the clips themselves, should be taped or covered with a suitable compound. Com- pound should not be used on border lights, as the heat from the lamps will cause the compound to melt and run down on the lamps. This also applies to any device of this form where the lamp hangs down, or below, the trough. In cases of this kind the clips should be taped, or, better, properly designed receptacles used. The footlight circuits may be wired for a capacity of 1,320 watts, this allowing 24-16 c. p. lamps, 18-24 c. p. lamps, or 12-32 c. p. lamps on one circuit. 4. Borders. a. Must be constructed of steel of a thickness not less than No. 20 gage, treated to prevent oxidation, be suitably stayed and supported by a metal framework, and so designed that flanges of reflectors will protect lamps. b. Must be so wired that no set of lamps requiring more than 1,320 watts will be dependent upon one cut-out. c. Must be wired in approved conduit, each lamp recep- tacle to be enclosed within an approved outlet box, the whole to be enclosed in a steel trough, or each lamp receptacle may be mounted on or in the cover of a steel box so constructed as to enclose all the wires and the live parts of receptacles, metal to be of a thickness not less than No. 20' gage. d. Must be provided with suitable guards to prevent LOW POTENTIAL SYSTEMS. 207 scenery or other combustible material coming in contact with lamps. e. Cables must be continuous from stage switchboard to border; conduit construction must be used from switchboard to point where cables must be flexible to permit of the rais- ing and lowering of border, and flexible portion must be enclosed in an approvexi fireproof hose or braid and be suit- ably supported. Junction Boxes will be allowed on fly floor and rigging loft In existing theaters where the wiring has been completed and approved by Inspection Department having jurisdiction. /. For the wiring of the border proper, wire with slow burning insulation should be used. g. Must be suspended with wire rope, same to be in- sulated from border by at least two approved strain insulators properly inserted. The design and construction of border lights is similar to that just described for footlights with the exception of the arrangement of the strips and the kind of wire used. Border lights are suspended above the stage and are de- signed to throw the light downward and slightly to the back of the stage. To produce the proper lighting efifects the 3 Figure 124. border must be capable of adjustment, both as to its height above the stage and its position. Figure 124 shows several forms of border lights. 208 MODERN ELECTKICAL CONSTRUCTION. Figure 125 shows a simple form of border light in com- mon use. It will be noticed that the flange of the reflector is carried around the lamps in such a manner as to protect them from accidental contact with the scenery. Figure 125. ] Figure 126 shows a completed border light with one method of suspension. The iron bands to which are fas- tened the supporting chains are carried entirely around the border frame and serve as a means of attaching it to its support and at the same time provide mechanical protec- tion for the lamps. These bands are placed from four to six feet apart. Figure 126. The cables which carry current to the border lights are generally made up for each individual installation, the size and number of wires varying according to the number and LOW POTENTIAL SYSTEMS. 209 combination of lamps used and the distance of the border from the stage switchboard or center of distribution. There are at the present time no specifications govern- ing the construction of border light cable, but in a general way it should comply with the following: The wire of the cable should be stranded, the wires composing the strands to be of such size as will allow of sufficient flexibility with the required strength. Each of the stranded wires should be covered with a wind of cotton as required for flexible cord and should then be covered with a rubber covering of about the same thickness as required for rubber covered wires of corresponding sizes. Each wire should have a stout braid which should be filled with a waterproofing compound. To round out the cable, jute, slightly impregnated with a waterproof compound, should be used. The whole cable should be covered with a tough outer braid of. such thick- ness as to provide proper protection with continued rough usage. No rubber need be used between this outer braid and the individual wires comprising the cable. In reference to the above specifications it might be well to state .that they are given simply as a guide to enable one to choose a cable suitable to the work. There are at the present .time no Underwriters' specifications covering this class of wire and there is considerable cable in use which is entirely unsuited to the purpose. The latest Underwriters' rules should be consulted before buying or ordering cable. Border cables must be continuous from the stage switch- board or center of distribution to the border itself, the ex- posed portion of the cable being protected by a fireproof braid or hose. This fireproof covering can be put on when the cable is manufactured or fireproof hose suitable for the purpose may be obtained from the manufacturers of this class of goods and placed on the ordinary cable. The cables 210 MODERN ELECTRICAL CONSTRUCTION. should be long enough to allow .the border to be lowered to within six or seven feet of the floor to permit of the neces- sary repairs and adjustments and the replacement of lamps. "Take-up" devices, which are attached to the cable to take up the slack when the border is raised, should be fastened to the cable by some suitable device which will give a large bearing surface so that the insulation of the cable will not be injured. The practice of simply tying a rope around the cable is very bad, as the rope is sure to cut into the insula- tion. As considerable heat is developed in a border light, due to the great number of lamps employed and to the position of the border itself, the rubber covering of the ordinary rubber covered wire would be very apt to become useless as an insulator, so that for this class of wiring slow-burning wire should be used. Specifications covering this wire are given under "Fittings." Wire rope must be used for the suspension of the border lights. The rope should be of such size as to properly sup- port the border with an ample safety factor. Generally three or four ropes are provided, each rope being fastened to a bridle which will distribute the s,train uniformly along the length of the border frame. Two strain insulators of the type shown in Figure 49 should be connected in the cable at the point where it connects to .the border. The sup- porting cables are generally run to counterweights, hemp ropes fastened to either the counterweights or the border itself serving as a means to raise and lower the border. Where the border is small and of inconsiderable weight the wire rope is run directly to the point of fastening and the adjustments made with it direct. 5. Stage Pockets. — Must be of approved type controlled from switchboard, each receptacle to be of not less than fifty LOAV POTENTIAL SYSTEMS. amperes rating, and each receptacle to be wired with a separate circuit to its full capacity. For the connection of portable apparatus on the stage, pockets are provided in the stage floor. These pockets con- tain receptacles into which the plugs connected to cables attached to the apparatus are inserted. The pockets should be made absolutely fireproof and .the receptacles should be so installed that all live parts will be clear of the opening. It would be a good rule to have stage plugs of different shapes to be used in connection with arc and incandescent lights, so that it will be impossible to plug incandescent lights on arc light circuits. An arc light circuit requires a fuse of about forty amperes. Many times a single incan- descent light is plugged into such a circuit. A short circuit occurring under these circumstances would be accompanied with disastrous results. Figvire 127 shows a s.tage pocket 2l2 MODERN ELECTRICAL CONSTRUCTION. with receptacles. The average stage pocket accommodates four receptacles. 6. Proscenium Side Lights. — Must be so installed that they cannot interfere with the operation of or come in con- tact with curtain. Those lights placed at the stage opening on the stage side of the wall which separates the stage from the audi- torium (proscenium wall) are known as the proscenium side lights. They are constructed in the same manner as the footlights previously described, with the exception of Figure 128. the reflectors, which are of various shapes. Figure 128 shows a common form of proscenium side light. The troughs are generally hinged so that they may be turned to illuminate any particular part of the stage, and special care should be exercised in placing them so that they cannot in any manner interfere with the operating of the curtain. It is sometimes advisable, especially in the case of vaudeville or burlesque houses, to provide a wire mesh screen for the protection of the lamps. 7. Scene Docks. — Where lamps are installed in Scene Docks, .they must be so located and installed that they will not be liable to mechanical injury. LOW POTENTIAL SYSTEMS. 213 As scene docks are often used for the storage of scenery and other stage paraphernaHa and as lights are generally placed on the side walls, a substantial guard should be pro- vided. This guard should be capable of standing considerable hard usage and should be firmly attached. The ordinary lamp guard fastened to the socket or lamp itself is useless as a protection. 8. Curtain Motors. — Must be of ironclad .type and in- stalled so as to conform to the requirements of the National Electrical Code. (See No. 8.) Rheostats used with curtain motors, if installed on the stage wall or in any o.ther location outside of the motor room, should be entirely enclosed and well protected, so that nothing of an inflammable nature can come in contact with them. 9. Control for Stage Flues. a. In cases where dampers are released by an electric device, the electric circuit operating same must be normally closed. b. Magnet operating damper must be wound to take full voltage of circuit by which it is supplied, using no resist- ance device, and must not heat more than normal for ap- paratus of similar construction. It must be located in loft above scenery and be installed in. a suitable iron box with a tight self-closing door. c. Such dampers must be controlled by at leas.t two standard single pole switches mounted within approved iron boxes provided with self-closing doors without lock or latch, and located, one at the electrician's station, and others as designated by ,the Inspection Department having jurisdic- tion. The dampers referred to are ventilators arranged above the stage and scenery. In case of fire it is essential that these be opened immediately to allow smoke to escape and 214 MODERN ELECTRICAL CONSTRUCTION. also to prevent the total consumption of oxygen in the build- ing by the flames. This rapid consumption of oxygen, mak- ing it very difficult for people to breathe, thereby causing frantic efforts at inhalation, which result in inhaling large quantities of smoke and overheated air, are perhaps the main causes of the enormous death loss usual in theater fires. Where current is obtained from an isolated plant which is shut down at night time and is not supplied with storage Figure 12 battery, or where alternating current is used, it is generally more satisfactory to use battery current for the operation of the damper, gravity ceils being used for this purpose. Where the installation is supplied by a direct current system which is continuous .the damper circuit may be taken directly from the system. Figure 129 shows an inexpensive form of damper control which is supplied by current from two or three cells of gravity battery. The lever arms are made from bar iron formed in the shapes shown. The magnet LOW POTENTIAL SYSTEMS. ^lO is of the type used in door openers and is enclosed in an iron box, that part of the enclosure immediately surround- ing .the magnet pole pieces being of brass. When the cir- cuit is opened the armature falls and strikes the lower arm a sharp blow, thus releasing the damper rope. To close the damper the circuit is first closed, the magnet armature is pulled back in place by the cord attached to the lower end of it, and the damper is closed, the ball in the damper rope engaging in the slot in the end of the lever arm, c. Dressing Rooms. 1. Must be wired in approved conduit, except that in existing buildings where it is impracticable to install ap- proved conduit, approved armored cable may be used, pro- vided it is installed in accordance with No. 24 A. 2. All pendant lights must be equipped with approved reinforced cord or cable. 3. All lamps must be provided with approved guards. Experience has proven it a difficult matter to arrange dressing rooms in such a way that actors cannot disar- range them and thus cause troubles of many kinds. One of the principal preventive devices is a lamp guard fastened .to each socket in such a way that it cannot be removed with- out assistance from the house electrician. This will prevent the removal of the lamp and the substitution of a lamp of greater candle power or of the portable devices which many actors carry that require much more current. A lamp guard so arranged that it can be locked on will readily accomplish the purpose and such lamp guards are on the market. The principal use of light in .the dressing rooms is for the "make-up" of the actors. One light on each side of every mirror, suitably placed, with one or two lights for gen- eral illumination, are generally sufficient. A receptacle for 2l6 MODERN ELECTRICAL CONSTRUCTION. curling iron connection can also be provided, but should also be under lock and key. d. Portable Equipments. 1. Arc lamps used for stage effects must conform to .the following requirements : — a. Must be constructed entirely of metal except where the use of approved insulating material is necessary b. Must be substantially constructed, and so designed as to provide for proper ventilation, and to prevent sparks being emitted from lamps when same is in operation, and mica must be used for frame insulation. c. Front opening must be provided with a self-closing hinged door frame in which wire gauze or glass must be in- serted, excepting lens lamps, where the front may be sta- tionary and a soHd door be provided on back or side. d. Must be provided with a one-sixteen.th-inch iron or steel guard having a mesh not larger than one inch, and be substantially placed over top and upper half of sides and back of lamp frame ; this guard to be substantially riveted to frame of lamp, and to be placed at a distance of at least two inches from the lamp frame. e. Switch on standard must be so constructed that acci- dental contact with any live portion of same will be im- possible. /. All stranded connections in lamp and at switch and rheostat must be provided with approved lugs. g. Rheostat, if mounted on standard, must be raised to a height of at least .three inches above floor line, and in ad- dition to being properly enclosed must be surrounded with a substantially attached metal guard having a mesh not larger than one square inch, which guard is to be kept at least one inch from outside frame of rheostat. h. A competent operator must be in charge of each arc lamp, except that one operator may have charge of two lamps when they are not more than ten feet apart and are so located that he can properly watch and care for both lamps. On the stage hand-feed arc lamps are used almost ex- LOW POTENTIAL SYSTEMS. 217 clusively and an operator is always required to look after the lamps. The style of lamps generally used are shown in Figures 130 and 131. Figure 130 shows the focusing or Figure 130. Figure 131. Spot lamp and Figure 131 the open box or olivet lamp, which is used for general illumination. These arc lamps require a MODERN ELECTRICAL CONSTRUCTION. <52P- .Osp.. .flap. -aao- -333- Rheostat No. S3. Hard line — One lamp on 220 volts, 20 amperes. Dotted line— One lamp on 110 volts, 30 amperes. Rheostat No. 82. One lamp on 110 volts, 60 amperes. Rheostat No. 83. Two lamps on 110 volts each, 15 amperes. Rheostat No. 82. Hard line — Two lamps on 220 volts each, 20 amperes. Dotted line— Two lamps on 110 volts each, 30 amperes. '[^' >«'.. <& ^ Rheostat No. 82. One lamp on 223 volts, 35 amperes. -£8f> 93C>- Rheostat No. 82. One lamp on 450 volts, 20 amperes. 03^'' 93% Rheostat No. 81. One lamp on 550 volts, 22 amperes. Figure 132. I LOW POTENTIAL SYSTEMS. current of from 20 to 40 amperes and should be wired for accordingly. Figure 132 shows diagrammatically a very useful form of rheostat for stage purposes. As most "shows" are constantly traveling, the apparatus carried by them should be adjustable in so far as voltage is concerned and also as to system, i. e., alternating or direct current. As will be seen from the figure, this rheostat lends itself to any voltage or system. This particular rheostat is manufactured by the Chicago Stage Lighting Co. 2. Bunches, a. Must be substantially constructed of metal and must not contain any exposed wiring. b. The cable feeding same must be bushed in an ap- proved manner where passing through the metal and must be properly secured to prevent any mechanical strain from coming on the connection. The bunch light is used in various locations around the stage where only a small amount of illumination is required. 3. Strips, a. Must be constructed of steel of a thick- ness not less than No. 20 gage, treated to prevent oxidation, and suitably stayed and supported by metal framework. b. Cable feeding must be bushed in an approved manner where passing through the metal, and must be properly se- cured to prevent any mechanical strain coming on the con- nections. Strip lights are laid on the floor and hung on the scenery and are used to illuminate those parts of the scenery where the lights from the foots and borders is obstructed. Any of the forms shown in Figure 119 may be used for footlight construction. Reflectors are generally provided which serve to concentrate the light on the spot desired and to protect the lamps from accidental contact. Special care must be given to cables, where they leave strips ; being portable, they soon suffer damage at these points. MODEEN ELECTRICAL CONSTRUCTION. 4. Poftahle Plugging Boxes. — Must be constructed that no current carrying part will be exposed, and each re- ceptacle must be protected by approved fuses mounted on slate or marble bases and enclosed in a fireproof cabinet equipped with self-closing doors. Each receptacle must be constructed to carry thirty amperes without undue heating, and the bus-bars must have a carrying capacity equivalent to Figure 133. the current required for the .total number of receptacles, allowing thirty amperes to each receptacle, and approved lugs must be provided for the connection of the master cable. When a number of pieces of electrical apparatus are to be used at one time on the stage, instead of carrying a separate cable from each piece of apparatus to a pocket, a portable LOW POTENTIAL SYSTEMS. 221 plugging box or spider box is used. This is shown in Figure 133. One large cable is carried from the plugging box to a pocket or other convenient point of connection and the various pieces of apparatus connected to .the plugging box by plugs and short cables. This greatly reduces the amount of cable used and allows of rapid assembly and removal. 5. Pin Plug Conductors, a. When of approved type may be used to connect approved portable lights and ap- pliances. b. Must be so installed that the "female" part of plug will be on the live end of cable and must be so constructed Figure 134. that tension on the cable will not cause any serious mechan- ical strain on the connections. 6. Lights on Scenery. — When brackets are used they must be wired entirely on the inside, fixture stem must come through to the back of the scenery and end of stem be properly bushed. The usual method of complying with this rule is shown in 222 MODEEN ELECTRICAL CONSTRUCTION. Figure 134. Everything about the bracket is of metal and stage cable is used to make the connection to the outside. 7. String or Festoon Lights. — Wiring for same should be approved cable, joints where taps are taken from same for hghts to be properly made, soldered and taped, and where lamps are used in lanterns or similar devices lamps must be provided with approved guards. Where taps are taken from cable, they should be so staggered that joints of different polarity will not come immediately opposite each other and must be properly protected from strain. Figure 135. A good method of making tap joints in festoons is shown in Figure 135. The joints are made staggering and properly soldered and taped with both rubber and friction tape. The cable which is tapped on is then carried along the main cable for three or four inches and securely taped. This removes nearly all the strain from the joints and pre- vents the wires from working loose. 8. Special Electrical Effects. — Where devices are used for producing special effects, such as lightning, waterfalls, etc., the apparatus must be so constructed and located that flames, sparks, etc., resulting from the operation cannot come in contact with combustible material. The necessity for electrical current in connection with stage effects has of late years been greatly reduced. Scenes and effects of almost any description can be produced by LOW POTENTIAL SYSTEMS. 223 means of transparent films attached to and rotating in front of an arc lamp. Celluloid films, if they remain stationary exposed to the light of an arc lamp, may be ignited in two or three seconds and burn very rapidly. Care must be exercised in the use of some of these effects, as the sudden and unexpected production of a fire efifect or of a puff of smoke or momentary blaze such as would be produced by a short circuit might have a disastrous effect on the audience. In Figure 136 a device is shown for producing lightning flashes. It consists of a solenoid, the core of which is at- Fig-uie iob tached to a lever fitted with a piece of carbon. The carbon rests on a piece of steel bar. When the circuit is closed the solenoid operates and raises the carbon from the piece of steel, a considerable flash resulting. The carbon continues I 224 MODERN ELECTRICAL CONSTRUCTION. to rise until the circuit opens, when it drops again, causing another flash, etc. e. Auditorium. 1. All wiring must be installed in approved conduit, ex- cept that in existing buildings where it is impracticable to in- stall approved conduit, approved armored cable may be used, provided it is installed in accordance with No. 24 A. 2. All fuses used in connection with lights illuminating all parts of the house used by the audience must be installed in fireproof enclosures so constructed that there will be a space of at least six inches between the fuses and the sides and face of enclosure. 3. Exit lights must no.t have more than one set of fuses between same and service fuses. The only fuses allowed on the exit light, circuits are the branch fuses and the fuses at the service. This necessitates running the exit light main, direct to the service, no.t changing size and not tapping onto any other main unless both mains are of equal carrying capacity. 4. Exit lights and all lights in halls, corridors or any other part of the building used by .the audience, except the general auditorium lighting, must be fed independently of the stage lighting, and must be controlled only from the lobby or other convenient place in front of the house. All sockets used on the exit and emergency lighting should be of the keyless type, so that they cannot be controlled from any point except the lobby. 5. Every portion of the theater devoted to the use or ac- commoda.tion of the public, also all outlets leading to the streets and including all open courts, corridors, stairways, exits and emergency exit stairways, should be well and prop- erly lighted during every performance, and the same should remain lighted until the entire audience has left the premises. To conform with this rule there should be provided in LOW POTENTIAL SYSTEMS. 225 the auditorium a sufficient number of lights to properly il- luminate it at all times. These lights should never be turned out while the audience is in the building. They should be supplied with current from the emergency mains and should be controlled from the lobby. 32. Car Wiring and Equipment of Cars. a. Protection of Car Body, etc. 1. Under side of car bodies to be protected by approved fire-resisting, insulating material, not leess than 1-8 inch in thickness, or by sheet iron or steel, not less than .04 inch in thickness, as specified in Section a, 2, 3 and 4. This pro- tection to be provided over all electrical apparatus, such as motors with a capacity of over 75 H. P. each, resistances, con- tactors, lightning arresters, air-brake motors, etc., and also where wires are run, except that protection may be omitted over wires designed to carry 25 amperes or less if they are encased in metal conduit. 2. At motors of over 75 H. P. each, fire-resisting mate- rial or sheet iron or steel .to extend not less than 8 inches beyond all edges of openings in motors and not less than 6 inches be3'ond motor leads on all sides. 3. Over resistances, contractors and lightning arresters, and other electrical apparatus, excepting when amply pro- tected by their casing, fire-resis,ting material or sheet iron or steel to extend not less than 8 inches beyond all edges of the devices. 4. Over conductors, not encased in conduit, and con- ductors in conduit when designed to carry over 25 amperes, unless the conduit is so supported as .to give not less than ^ inch clear air space between the conduit and the car, fire- resisting material or sheet iron or steel to extend at least 6 inches beyond conductors on either side. The fire-resisting- insulating- material or sheet iron or steel may be omitted over cables made up of flame-proof braided outer covering- when surrounded by 1-8 inch flame- proof covering-, as called for by Section i, i. ■ 5. In all cases fireproof material or sheet iron or steel 226 MODERN ELECTRICAL CONSTRUCTION. to have joints well fitted, to be securely fastened to the sills, floor timbers and cross braces, and to have the whole sur- face treated with a waterproof paint. 6. Cut-out and switch cabinets to be substantially made of hard wood. The entire inside of cabinet to be lined with not less than 1-8 inch fire-resisting insulating material which shall be securely fastened to the woodwork, and after the fire-resisting material is in place the inside of the cabinet shall be treated with a waterproof paint. b. Wires, Cables, etc. 1. All conductors to be stranded, the allowable carrying capacity being determined by Table "A'' of No. 16, except that motor, .trolley and resistance leads shall not be less than No. 7 B. & S. gage, heater circuits not less than No. 12 B. & S. gage, and lighting and other auxiliary circuits not less than No. 14 B. & S. gage. The current used in determining the size of motor, trolley and resistance leads shall be the per cent of .the full load current, based on one hour's run of the motor, as given by the following table : Size each motor. Motor Leads. Trolley Leads. Resistance Leads. 75 H. P. or less Over 75 H. P. 50% 45% 40% 35% 15% 15% Fixture wire complying with No. 46 will be permitted for wiring- approved clusters. 2. To have an insulation and braid as called for by No. 41 for wires carrying currents of the same potential. 3. When run in metal conduit, to be protected by an additional braid as called for by No. 47. "Where conductors are laid in conduiu not being drawn through, the additional braid will not be required. 4. When not in conduit, in approved moulding, or in cables surrounded by ]4, inch flameproof covering, must com- ply with the requirements of No. 41 (except that tape may be substituted for braid) and be protected by an additional flameproof braid, at least 1-32 inch in thickness, the outside being saturated with a preservative flameproof compound. LOW POTENTIAL SYSTEMS. 227 This rule will be interpreted to include the leads from the motors. 5. Must be so spliced or joined as to be both mechan- ically and electrically secure without solder. The joints must then be soldered and covered with an insulation equal .to that on the conductors. Joints made with approved splicing devices and those con- necting' the. leads at motors, plows or third rail shoes need not be soldered. 6. All connections of cables to cut-outs, switches and fittings, except those to controller connection boards, when designed to carry over 25 amperes, must be provided with lugs that will grip .the conductor between the screw and the lug, the screws being provided with flat washers ; or by block terminals having two set screws, and the end of the conductors must be dipped in solder. Soldering, in ad- dition to the connection of the binding screws, is strongly recommended, and will be insisted upon when above require- ments are not complied with. This rule will not be construed to apply to circuits where the maximum potential is not over 25 volts and current does not exceed 5 amperes. c. Cut-outs, Circuit Breakers and Szvitchcs. 1. All cut-outs and switches having exposed live metal parts to be located in cabinets. Cut-outs and switches, not in iron boxes or in cabinets, shall be mounted on not less than ^ inch fire-resis.ting insulating material, which shall pro- ject at least >4 inch beyond all sides of the cut-out or switch. 2. Cut-outs to be of the approved cartridge or approved blow-out type. 3. All switches controlling circuits of over 5 ampere capacity shall be of approved single pole, quick break or ap- proved magnetic blow-out type. Switches controlling circuits of 5 ampere or less capacity may be of the approved single pole, double break, snap type. 4. Circuit breakers to be of approved type. 5. Circuits must no.t be fused above their safe carrying capacity. 6. A cut-out must be placed as near as possible to the 228 MODEKN ELECTRICAL CONSTRUCTION. current collector, so that the opening of the fuse in this cut-out will cut off all current from the car. When cars are operated by metallic return circuits, with circuit breakers connected to both sides of the circuit, fuses in addition to the circuit breakers will be required. d. Conduit. When from the nature of the case, or on account of the size of the conductors, the ordinary pipe and junction box construction is not permissible, a special form of conduit system may be used, provided the general requirements as g-iven below are complied with. 1. Metal conduits, outlet and junction boxes to be con- structed in accordance with Nos. 49 and 49A, except that conduit for lighting circuits need not be over 5-16 inch inter- nal diameter and 1-2 inch external diameter, and for heating and air motor circuits need not be over 3-8 inch internal diameter and 9-16 inch external diameter, and all conduits where exposed to dampness must be water tight. 2. Must be continuous between and be firmly secured into all outlet or junction boxes and fittings, making a thorough mechanical and electrical connection l;)etween same. 3. Metal conduits, where they enter all outlet or junction boxes and fittings, must be provided with approved bushings fitted so as to protect cables from abrasion. 4. Except as noted in Section i, 2, must have the metal of the conduit permanently and efifectively grounded. 5. Junction and outlet boxes must be installed in such a manner as to be accessible. 6. All conduits, outlets or junction boxes and fittings to be firmly and substantially fastened to the framework of the e. Moulding 1. To consist of a backing and a capping and to be con- structed of fire-resisting insulating material, except that it may be made of hard wood where the circuits which it is designed to support are normally not exposed to moisture. LOW POTENTIAL SYSTEMS. 229 2. When constructed of fire-resisting insulating material, the backing shall be not less than 1-4 inch in thickness and be of a width sufficient to extend not less than 1 inch beyond conductors at sides. The capping, to be not less than Vs inch in thickness, shall cover and extend at least ^ inch beyond conductors on either side. The joints in the moulding shall be mitered to fit close, the whole material being firmly secured in place by screws or nails and treated on the inside and outside with a waterproof paint. When fire-resisting- moulding- is used over surfaces already protected by 1-8 inch fire-resisting- insulating- material no backing will be required. 3. Wooden mouldings must be so constructed as to thor- oughly encase the wire and provide a thickness of not less than 3-8 inch at the sides and back of the conductors, the capping being not less than 3-16 inch in thickness. Must have both outside and inside two coats of waterproof paint. The backing and the capping shall be secured in place by screws. /. Lighting and Lighting Circuits 1. Each outlet to be provided with an approved porcelain receptacle, or an approved cluster. No lamp of over 32 candle power .to be used. 2. Circuits to be run in approved metal conduit or ap- proved moulding. 3. When metal conduit is used, except for sign lights, all outlets to be provided with approved outlet boxes. 4. At outlet boxes, except where approved clusters are used, porcelain receptacles to be fastened to the inside of the box and the metal cover to have an insulating bushing around opening for the lamp. When approved clusters are used, the cluster shall be thoroughly insulated from the metal conduit, being mounted on a block of hard wood or fire-resisting insulating mate- rial. 230 MODERN ELECTIilCAL CONSTRUCTION, 5. Where conductors are run in moulding the porce- lain receptacles or cluster to be mounted on blocks of hard wood or of fireproof insulating material. g. Heaters and Heating Circuits 1. Heaters to be of approved type. 2. Panel heaters to be so constructed and located that when heaters are in place all current carrying parts will be at leas.t 4 inches from all woodwork. Heaters for cross seats to be so located that current carrying parts will be at least 6 inches below under side of seat, unless under side of seat is protected by not less than 1-4 inch fire-resisting insulating material, or .04 inch sheet metal with 1 inch air space over same, when the distance may be reduced to 3 inches. 2. Circuits to be run in approved metal conduit, or in approved moulding, or if the location of conductors is such as will permit an air space of not less than 2 inches on all sides except from the surface wired over they may be sup- ported on porcelain knobs or cleats, provided the knobs or cleats are mounted on not less than 1-4 inch fire-resisting in- sulating material extending at least 3 inches, beyond con- ductors at either side, the supports raising the conductors not less than 1-2 inch from the surface wired over and being not over 12 inches apart. h. Air Pump Motor and Circuits. 1. Circuits to be run in approved metal conduit or in approved moulding, except that when run below the floor of the car they may be supported on porcelain knobs or cleats, provided the supports raise the conductor at least 1-2 inch from the surface wired over and are not over 12 inches apart. 2. Automatic control to be enclosed in approved metal box. Air pump and motor, when enclosed, to be in ap- proved metal box or wooden box lined with metal of not less than 1-32 inch thickness. When conductors are run in metal conduits the boxes surrounding automatic control and air pump and motors may serve as outlet boxes. LOW rOTENTIAL SYSTEMS. /. Main Motor Circuits and Devices 1. Conductors connecting between trolley stand and main cut-oiit or circuit breakers in hood to be protected where wires enter car to prevent ingress of moisture. 2. Conductors connecting between third rail shoes on same truck to be supported in an approved fire-resis.ting in- sulating moulding or in approved iron conduit supported by soft rubber or other approved insulating cleats. 3. Conductors on .the under side of the car, except as noted in Section i, 4, to be supported in accordance with one of the following methods : a. To be run in approved metal conduit, junction boxes being provided where branches in conduit are made and outlet boxes where conductors leave conduit. b. To be run in approved fire-resisting insulating mould- ing. c. To be supported by insula.ting cleats, the supports being not over 12 inches apart. 4. Conductors with flameproof braided outer covering, connecting between controllers a.t either end of car, or con- trollers and contactors, may be run as a cable, provided the cable where exposed to the weather is encased in a canvas hose or canvas tape, thoroughly taped or sewed at ends and where taps from the cable are made, and the hose or tape enters the controllers. Conductors with or without flameproof braided outer cov- ering connecting between controllers at either end of the car, or controllers and contactors, may be run as a cable, provided the cable throughout its entire length is surrounded by 1-8 inch flameproof covering, thoroughly taped or sewed at ends, or where taps from cable are made, and the flame- proof covering enters the controllers. , Cables where run below floor of car may be supported by approved insula^ting straps or cleats. Where run above floor of car, to be in a metal conduit or wooden box painted on the inside with not less than two coats of flameproof paiut, and where this box is so placed that it is exposed to water, as by washing of the car floor, attention should be given to making the box reasonably waterproof. 232 MODERN ELECTRICAL CONSTRUCTION. Canvas hose or tape, or flameproof material surrounding cables after conductors are in same, to have not less than two coats of waterproof insulating material. 5. Motors to be so drilled that, on double truck cars, connecting cables can leave motor on side neares.t to king bolt. 6. Resistances to be so located that there will be at least 6 inch air space between resistances proper and fire-resisting material of the car. To be mounted on iron supports, being insulated by non-combustible bushings or washers, or the iron supports shall have at least 2 inches of insulating sur- face between them and metal work of car, or the resistances may be mounted on hardwood bars, supported by iron stir- rups, which shall have not less than 2 inches of insulating surface between foot of resis.tance and metal stirrup, the entire surface of the bar being covered with at least 1-8 inch fire-resisting insulating material. The insulation of the conductor, for about 6 inches from terminal of the resistance, should be replaced, if any in- sulation is necessary, by a porcelain bushing or asbestos sleeve. 7. Controllers to be raised above platform of car by a not less than 1 inch hardwood block, the block being fitted and painted to prevent moisture working in between it and the platform. j. Lightning Arresters 1. To be preferably located .to protect all auxiliary cir- cuits in addition to main motor circuits. 2. The ground conductor shall be not less than No. 6 B. & S. gage, run with as few kinks and bends as possible, and be securely grounded. k. General Rules 1. When passing through floors, conductors or cables' must be protected by approved insulating bushings, which shall fit the conductor or cable as closely as possible. 2. Mouldings should never be concealed except where readily accessible. Conductors should never be tacked into moulding. LOW POTENTIAL SYSTEMS, 233 3. Short bends in conductors should be avoided where possible. 4. Sharp edges in conduit or in moulding must be smoothed to prevent injury to conductors. 33. Car Houses. a. The trolley wires must be securely supported on in- sulating hangers. b. The trolley hangers must be placed at such a distance apart that, in case of a break in the trolley wire, contact with the floor cannot be made. c. Must have an emergency cut-out switch located at a proper place outside of the building, so that all the trolley wires in the building may be cut out at one point, and line insulators must be installed, so that when this emergency switch is open, the trolley wire will be dead at all points within 100 feet of the building. The current must be cut out of the building when not needed for use in the build- ing. This may be done by the emergency switch, or if preferred a second switch may be used that will cut out all current from the building-, but which need not cut out the trolley wire outside as would be the case with the emergency switch. d. All lamps and stationary motors must be installed in such a way that one main switch may control the whole of each installation, lighting and power, independently of the main cut-out switch called for in Section c. e. Where current for lighting and stationary motors is from a grounded trolley circuit, the following special rules to apply: 1. Cut-outs must be placed between the non-grounded side and lights or motors they are to protect. No set or group of incandescent lamps requiring over 2,000 watts must be dependent upon one cut-out. 2. Switches must be placed between non-grounded side and lights and motors they are to protect. 234 MODERN ELECTIUCAL CONSTRUCTION. 3. Must have all rails bonded at each joint with a con- ductor having a carrying capacity at least equivalent to No. 00 B. & S. gage annealed copper v^ire, and all rails must be connected to the outside ground return circuit by a not less than No. 00 B. & S. gage copper wire or by equivalent bonding through the track. All lighting and stationary motor circuits must be thor- oughly and permanently .connected to the rails or to the wire leading to the outside ground return circuit f. All pendant cords and portable conductors will be con- sidered as subject to hard usage (see 45-/). g. Must, except as provided in Section e, have all wiring and apparatus installed in accordance with the rules for con- stant potential systems. h. Must not have any system of feeder distribution cen- tering in the building. i. Cars must not be left with the trolley in electrical con- nection with the trolley wure. 34. Lighting and Power from Railway Wires. a. Must not he permitted under any pretense, in the same eircuit with trolley zvires zvith a ground return, except in elc trie railway cars, electric car houses and their pozver stations, nor shall the same dynamo he used for both purposes. HIGH-POTENTIAL SYSTEMS. 550 TO 3,500 Volts. Any circuit attached to any machine or comhinatinn of ma- chines zvhich develops a diif(^rencc of potential, between any tzvo wires, of over 550 volts and less than. 3,500 volts, shall be considered as a high-potential circnit, and as coming under that class, unless an approz'cd transforming device is used, zvhich cuts the difference of potential down to 550 volts or less. (See note following- first paragraph under Low-Potential systems. HIGH POTENTIAL SYSTEMS. 2d5 35. Wires. (See also Nos. 14, 15 and 16.) a. Must have an approved rubber-insulating covering (see No. 41). h. Must be always in plain sight and never encased, ex- cept as provided for in No. 8 h, or where required by the In- spection Department having jurisdiction. c. Must (except as provided for in No. 8 h) , be rigidly supported on glass or porcelain insulators, which raise the wire at least one inch from .the surface wired over, and must be kept about eight inches apart. Rigid supporting- requires, under ordinary conditions, where wiring along flat surfaces, supports at least about every four and one-half feet. Tf the wires are unusually liable to be disturbed, the distance between supports should be shortened. In buildings of mill construction, mains of No. 8 B. & S. gage or over, where not liable to be disturbed, may be sep- arated about ten inches and run from timber to timber, not breaking around, and may be supported at each timber only. d. Must be protected on side walls from mechanical injury by a substantial boxing, retaining an air space of one inch around the conductors, closed at the top (the wires passing through bushed holes) and extending not less than seven feet from the floor. When crossing floor timbers, in cellars, or in rooms where they might be exposed to injury wires must be attached by their insulating supports to the under side of a wooden strip not less than one-half an inch in thickness. For general suggestions on protection, see note under No. 24 e. See also note under No. 18 e. 36. Transformers. (When permitted mside buildings, see No. 13.) (For construction rules, see No. 62.) (See also Nos. 13 and 13 A.) Transformers must not be placed inside of buildings with- out special permission from the Inspection Department having jurisdiction. 236 MODERN ELECTRICAL CONSTRUCTION. ! a. Must be located as near as possible to the point at which the primary wires enter the building. h. Must be placed in an enclosure constructed of fire- resisting material ; the enclosure to be used only for this pur- pose, and to be kept securely locked, and access to the same allowed only to responsible persons. c. Must be thoroughly insulated from the ground, or permanently and effectually grounded, and the enclosure in which they are placed must be practically air-tight, except that it must be thoroughly ventilated to the out-door air, if possible, through a chimney or flue. There should be at least six inches air space on all sides of the transformer. 37. Series Lamps. a. No multiple series or series multiple system of light- ing will be approved. h. Must not, under any circumstances, be attached to gas fixtures. EXTRA-HIGH-POTENTIAL SYSTEMS. Over 3,500 Volts. Any circuit attached to any machine or combination of ma- chines zvhich develops a difference of potential, between any two wires, of over 3,500 volts, shall be considered as an extra-high-potential circuit, and as coming under that class, unless an approved transforming device is used, which cuts the difference of potential down to 3,500 volts or less. 38. Primary Wires. a. Must not be brought into or over buildings, except power stations and sub-stations. EXTRA HIGH POTENTIAL SYSTEMS. 237 39. Secondary Wires. , a. Must be installed under rules for high-potential sys- tems when their immediate primary wires carry a current at a potential of over 3,500 volts, unless the primary wires are installed in accordance with the requirements as given in rule 12 A or are entirely underground, within city, town and village limits. NOTICE— DO NOT FAIL TO SEE WHETHER ANY RULE OR ORDINANCE OF YOUR CITY CONFLICTS WITH THESE RULES. Class D. FITTINGS, MATERIALS AND DETAILS OF CONSTRUCTION. (Light, Power and Heat. For Signaling Systems see Class E.) ALL SYSTEMS AND VOLTAGES. The following rules are hut a partial outline of require- ments. Devices or material zvhich fulfill the conditions of these requirements and no more will not necessarily' be ac- ceptable. All fittings and materials should be submitted for examination and test before bring introduced for use. INSULATED WIRES— Rules 40 to 48. 40. General Rules. a. Copper for insulated solid conductors of No. 4 B. & S. gage and smaller must not vary in diameter more than .002 of an inch from the standard. On solid sizes larger than No. 4 B. & S. gage the diameter shall not vary more than one per cent from the specified s.tandard. The conductivity of solid conductors shall not be less than 97% of that of pure copper of the specified size. In all stranded conductors the sum of the circular mils of the individual wires shall not be less than the nominal cir- cular mils of the strand by more than one and one-half per FITTINGS^ MATERIALS;, ETC. cent. The conductivity of the individual wires in a strand shall not be less than is given in the following table: Number Per cent 14 and larger 97.0 , 15 96.8 16 96.6 17 96.4 18 96.2 19 96.0 20 95.8 21 95.6 22 95.4 23 95.2 24 95.0 25 94.8 26 94.6 27 94.4 28 94.2 29 94.0 30 93.8 Standard for diameters and mlleag-es shall be that The adopted by the American Institute of Electrical Engineers. h. Wires and cables of all kinds designed to meet the following specifications must have a distinctive marking" the entire length of the coil, so that they may be readily identi- fied in the field. They must also be plainly tagged or marked as follows : 1. The maximum voltage at which the wire is designed to be used. 2. The words "National Electrical Code Standard." 3. Name of the manufacturing company and, if desired, trade name of the wire. 4. Month and year when manufactured. Wires described under Nos. 42, 43 and 44 need not have the distinctive marking, but are to be tagged. 41. Rubber-Covered Wire. a. Copper for conductors must be thoroughly tinned. Insulation for Voltages, to 600 inclusive. h. Must be of rubber or other approved substances, 240 MODERN ELECTRICAL CONSTRUCTION. homogeneous in character, adhering to the conductor and of a thickness not less than that given in the following table: B. & S. Gage. Thickness. 18 to 16 1-32 inch 15 to 8 . . . .3-64 4. 7 to 2 . . . .1-16 a 1 to 0000 5-64 M Circular Mils. 250,000 to 500,000. . . . . .3-32 .. 500 000 to 1 000,000. . .7-64 « Over 1 000 000. . 1-8 « Measurements of thinnest portion of insulating- wall the dielectric. are to be made at the c. The completed coverings must show an insulation re- sistance of at least 100 megohms per mile during thirty days' immersion in water at 70 degrees Fahrenheit (21 degrees Centigrade). d. Each foo.t of the completed covering must show a dielectric strength sufficient to resist throughout five minutes the application of an electro-motive force proportionate to the thickness of insulation in accordance with the following table : Thickness in 64th inches. 1 2 3 4 6 6 7 8 10 12 14 16 The source of alternating electro-motive force shall be a transformer of at least one kilowatt capacity. The application of the electro-motive force shall first be made at 4,000 volts for five minutes and then the voltage increased by steps of not over 3,000 volts, each held for five minutes, until the rupture of the insulation occurs. The test for dielectric strength shall be made on a sample of wire which has been immersed in Breakdown Test on 1 foot. 3,000 Volts A. C. 6,000 9,000 11,000 13,000 15,000 16,500 18,000 21,000 23.500 26,000 28,000 " FITTINGS,, MATERIALS, ETC. 241 water for seventy-two hours. One foot of wire under test is to be submerged in a conductino; liquid held in a metal trough, one of the transformer terminals being connected to the copper of the wire and the other to the metal of the trough. Insulations for Voltages between 600 and 3,500. e. The thickness of the insulating wall must not be less than that given in the following table: B. & S. Gage. Thickness. 14 to 1 3-32 inch. to 0000 3-32 inch, covered by tape or braid. Circular Mils. 250,000 to 500,000 3-32 inch, covered by tape or braid. Over 500,000 1-8 inch, covered by tape or braid. f. The requirements as to insulation and break-down re- sistance for wires for low-potential systems shall apply, with the exception that an insulation resistance of not less than 300 megohms per mile shall be required. Insulation for Voltage over 3,500. g. Wire for arc-light circuits exceeding 3,500 volts poten- tial must have an insulating wall not less than three-six- teenths of an inch in thickness, and shall withstand a break- down test of at least 23,500 volts and have an insulation of at least 50O megohms per mile. The tests on this wire to be made under the same condi- tions as for low-potential wires. Specifications for insulations for alternating- currents ex- ceeding 3,500 volts have been considered, but on account of the somewhat complex conditions in such work it has so far been deemed Inexpedient to specify general insulations for this use. General. h. The rubber compound or other approved substance used as insulation must be sufificiently elastic to permit all wires smaller than No. 7 B. & S. gage and larger than No. 11 B. & S. gage to be bent without injury to the insulation 242 MODERN ELECTRICAL CONSTRUCTION. around a cylinder twice the diameter of the insulated wire measured over the outer covering. All v^ires No. 11 B. & S. gage and smaller to be bent without injury to the insulation around a cylinder equal to the diameter of the insulated wire measured over .the outer covering. i. All of the above insulations must be protected by a substantial braided covering, properly saturated with a pre- servative compound. This covering must be sufficiently strong to withstand all the abrasion likely to be met with in 1 ^^^ Fig-ure 138. practice, and must substantially conform to approved sam- ples submitted by the manufacturer. 42. Slow-burning Weatherproof Wire. (See Figure 138.) This wire Is not as burnable as "weatherproof" nor as subject to softening under heat. It is not suitable for outside work. a. The insulation must consist of two coa.tings, one to be fireproof in character and the other to be weatherproof. The fireproof coating must be on the outside and must comprise about six-tenths of the total thickness of the wall. The com- pleted covering must be of a thickness not less than that given in the following table : B. & S. Gage. Thickness. 14 to 8 3-64 Inch 7 to 2 •. 1-16 1 to 0000 5-64 Circular Mils. 250,000 to 500,000 3-32 500,000 to 1,000,000 7-64 Over 1,000,000 1-8 Measurements of insulating- wall are to be made at the thinnest portion of the dielectric. h. The fireproof coating shall be of the same kind as that FITTINGS, MATERIALS, ETC. 243 required for "slow-burning wire," and must be finished with a hard, smooth surface. c. The weatherproof coating shall consist of a stout braid, applied and treated as required for "weatheroroof 43. Slow-burning Wire. a. The insulation must consist of three braids of cotton or other thread, all the interstices of which must be filled with the fireproofing compound or with material having equivalent resisting and insulating properties. The outer braid m.ust be specially designed to withstand abrasion, and Figure 139. its surface must be finished smooth and hard. The com- pleted covering must be of a thickness not less than that given in the table under No. 42 a. The solid constituent of the fireproofing compound must not be susceptible to moisture, and must not burn even when ground in an oxidizable oil, making a compound which, while proof against fire and moisture, at the same time has consider- able elasticity, and which when dry will suffer no change at a temperature of 250 degrees Fahrenheit (121 degrees Centi- grade), and which will not burn at even a higher temperature. This is practically the old so-called "underwriters" insula- tion. It is especially useful in hot, dry places where ordinary insulations would perish, and where wires are bunched, as on the back of a large switchboard or in wire tower, so that the accumulation of rubber insulation would result in an objectionably large mass of highly inflammable material. 44. Weatherproof Wire. (See Figure 139.) a. The insulating covering shall consist of at least three braids, all of which must be thoroughly saturated with a dense moisture-proof compound, applied in such a manner as to drive any atmospheric moisture from the cotton braiding, 244 MODERN ELECTRICAL CONSTRUCTION. thereby securing a covering to a great degree waterproof and of high insulating power. This compound must retain its elasticity at deg. Fahr. and must not drip at 160 deg. Fahr. The thickness of insulation must not be less than that given in the table No. 42 A, and the outer surface must be thoroughly slicked down. This wire is for use outdoors, where moisture is certain and where fireproof qualities are not necessary. 45. Flexible Cord. (For installation rules, see No. 28.) a. Must, except as required for portable heating ap- paratus (see section g), be made of stranded copper con- ductors, each strand to be not larger than No. 26 or smaller * Figure 140. than No. 30 B. & S. gage, and each stranded conductor must be covered by an approved insulation and protected from me- chanical injury by a tough, braided outer covering. For Pendant Lamps. (See Figure 140.) In this class is to be included all flexible cord which, under usual conditions, hang's freely in air, and which is not likely to be moved sufficiently to come in contact with surrounding objects. It should be noted that pendant lamps provided with long cords, so that they can be carried about or hung over nails or on machinery, etc., are not included in this class, even though they are usually allowed to hang freely in air. h. Each stranded conductor must have a carrying capacity equivalent to not less than a No. 18 B. & S. gage wire. c. The covering of each stranded conductor must be made up as follows: 1. A tight, close wind of fine cotton. 2. The insulation proper, which shall be waterproof. FITTINGS^ MATEKIALS^ ETC. 245 3. An outer cover of silk or cotton. The wind of cotton tends to prevent a broken strand punc- turing the insulation and causing a short circuit. It also keeps the rubber from corroding the copper. d. The insula.tion must be solid, at least one thirty-second of an inch thick, and must show an insulation resistance of fifty megohms per mile throughout two weeks' immersion in water at 70 degrees Fahrenheit, and stand the tests prescribed for low-tension wires as far as they apply. e. The outer protecting braiding should be so put on and sealed in place that when cut it will not fray out and where cotton is used it should be impregnated with a flameproof paint, which will not have an injurious effect on the insula- tion. For Portables. (See Figure 141.) In this classi is included all cord used on portable lamps, small portable motors, or any device which is liable to be carried about. /. Flexible cord for portable use except in offices, dwell- ings or similar places, where cord is not liable to rough usage and where appearance is an essential feature, must meet all the requirements for flexible cord for "pendant lamps," both Figure 141. as to construction and thickness of insulation, and in addi- tion mus.t have a tough braided cover over the whole. There must also be an extra layer of rubber between, the outer cover and the flexible cord^, and in moist places the outer cover must be saturated with a moisture-proof compound, thoroughly slicked down, as required for "weatherproof wire" in No. 44. In offices, dwellings, or in similar places where cord is not liable to rough usage and where appearance is an essential feature, flexible cord for portable use must meet all of the requirements for flexible cord for "pendant lamps," 246 MODEEN ELECTKICAL CONSTRUCTION. both as to construction and thickness of insulation, and in ad- dition must have a tough, braided cover over the whole, or providing there is an extra layer of rubber between the flexible cord and the outer cover, the insulation proper on each stranded conductor of cord may be 1-64 of an inch thickness instead of 1-32 of an inch as required for pendant cords. Flexible cord for portable use may, instead of the outer coverings described above, have an approved metal flexible armor. For Portable Heating Apparatus. (See Figure 11^2.) Applies to all smoothing and sad irons and to any other device requiring over 250 watts. g. Must be made as follows : 1. Conductors must be of braided copper, each strand not to be larger than No. 30 or smaller than No. 36 B. & S. gage. When conductors have a greater carrying capacity than No. 12 B. & S. gage they may be braided or stranded with each strand as large as No. 28 B. & S. gage. If stranded there must be a tight, close wind of cotton between the 'conductor and the insulation. Figure 142. An insulating covering of rubber or other approved material not less than one sixty-fourth inch in thick- ness. A braided covering of not less than one thirty-second inch thick, composed of best quality long fiber as- bestos, containing not over 5 per cent of vegetable fiber. The several conductors comprising the cord to be en- closed by an outer reinforcing covering not less than one sixty-fourth inch thick, especially designed to resist abrasion, and so treated as to prevent the cover from fraying. FITTINGS, MATEKIALS, ETC. 247 46. Fixture Wire. ( See Fig2ire 14J. ) (For installation rules, see No. 24 v to y.) a. May be made of solid or stranded conductors, with no strands smaller than No. 30 B. & S. gage, and must have a carrying capacity not less than that of a No. 18 B. & S. gage wire. b. Solid conductors must be thoroughly tinned. If a stranded conductor is used, it must be covered by a tight, close wind of fine cotton. e. Must have a solid rubber insulation of a thickness not less than one thirty-second of an inch for Nos. 18 to 16 B. & S. gage, and three sixty-fourths of an inch for Nos. 14 to 8 B. & S. gage, except that in arms of fixtures not exceeding twenty-four inches in length and used to supply not more than one sixteen-candle-power lamp or its equivalent, which are Figure 143. so constructed as to render impracticable the use of a wire with one thirty-second of an inch thickness of rubber insula- tion, a thickness of one sixty-fourth of an inch will be permit- ted. d. Must be protected with a covering at least one sixty- four.th of an inch in thickness, sufficiently tenacious to with- stand the abrasion of being pulled into the fixture, and suf- ficiently elastic to permit the wire to be bent around a cylinder with twice the diameter of the wire without in- jury to the braid. e. Must successfully withstand the tests specified in Nos. 41 c and 41 d. In wiring- certain designs of show-case fixtures, ceiling bulls-eyes and similar appliances in which the wiring is exposed to temperatures in excess of 120 degrees Fahrenheit (49 degrees Centigrade), from the heat of the lamps, slow- burning wire may be used (see No. 43). All such forms of fixtures must be submitted for examination, test and approval before being introduced for use, 248 MODERN ELECTRICAL CONSTRUCTION. 47. Conduit Wire. (For installation rules, see No. 24 n. to p.) a. Single wire for lined conduits must comply with the^ requirements of No. 41 (Figure 144). For unlined con- ] duits it must comply with the same requirements — except that ^'' Figure 144. Figure 145. Figure 146. tape may be substituted for braid — and in addition there must be a second outer fibrous covering, at least one thirty-second of an inch in thickness and sufficiently tenacious to with- stand the abrasion of being hauled through the metal con- duit (Figures 145 and 146). b. For twin or duplex wires in lined conduit, each con- ductor must comply with the requirements of No. 41 — except that tape may be substituted for braid on the separate con- ductors — and must have a substantial braid covering the whole. For unlined conduit, each conductor must comply with requirements of No. 41 — except that tape may be sub- stituted for braid — and in addition must have a braid covering the whole, at least one thirty-second of an inch in thick- ness and sufficiently tenacious to withstand the abrasion of being hauled through the metal conduit (Figure 147). c. For concentric wire, the inner conductor must comply with the requirements of No. 41 — except that tape may be Figure 147. Figure 148. substituted for braid — and there must be outside of the outer conductor the same insulation as on the inner, the whole to be covered with a substantial braid, which for unlined conduits must be at least one thirty-second of an inch in thickness, and sufficiently tenacious to withstand the abrasion of being hauled through the metal conduit. (Figure 148), riTTINGS, MATERIALS, ETC. 249 The braid or tape required around each conductor in duplex, twin and concentric cables is to hold the rubber insulation in place and prevent jamming- and flattening. All the braids specified in this rule must be properly sat- urated with a preservative compound. 48. Armored Cable. (See Figure 149.) (For installation rules, see No. 24A.) a. The armor of such cables must have at least as great strength to resist penetration of nails, etc., as is required for Figure 149. metal conduits (see No. 49 h), and its thickness must not be less than that specified in the following table : Nominal Actual Actual Internal Internal External Thickness Diameter. Diameter. Diameter. of Wall. Inches. Inches. Inches. Inches. Vs .27 .40 .06 1/4 .36 .54 .08 % .49 .67 .09 % .62 .84 .10 % .82 1.05 .11 1 1.04 1.31 .13 1^ 1.38 1.66 .14 1% 1.61 1.90 .14 2 2.06 2.37 .15 2»^ 2.46 2.87 .20 3 3.06 3.50 .21 3y2 3.54 4.00 .22 4 4.02 4.50 .23 4% 4.50 5.00 .24 6 5.04 5.56 .25 6 6.06 6.62 .28 250 MODERN ELECTRICAL CONSTRUCTION. An allowance of two one-hundredths of an inch for variation - in manufacturing- and loss of thickness by cleaning- will be permitted. b. The conductors in same, single wire or t-win conduc- tors, must have an insulating covering as required by No. 41 ; if any filler is used to secure a round exterior, it must be im- pregnated with a moisture repellent, and the whole bunch of conductors and fillers must have a separate exterior covering. 49. Interior Conduits. (For installation rules, see Nos. 24 n to p and 23.) a. Each length of conduit, whether lined or unlined, must have the maker's name or initials stamped in the n.etal or at- tached thereto in a satisfactory manner, so that inspectors can readily see .the same. The use of paper stickers or tag-s cannot be considered satisfactory methods of marking-, as they are readily loosened and lost off in the ordinary handling- of the conduit. Metal Conduits with Lining of Insulating Material. (See Figure 150.) b. The metal covering or pipe must be at least as strong as the ordinary commercial forms of gas pipe of the same Figure 150. size, and its thickness must be not less than that of standard gas pipe as specified in the table given in No. 48. c. Must not be seriously affected externally by burning out a wire inside the tube when the iron pipe is connected to one side of the circuit. d. Must have the insulating lining firmly secured to the pipe. e. The insulating lining must not crack or break when a length of the conduit is uniformly bent at temperature of 212 FITTINGS, MATERIALS, ETC. 251 degrees Fahrenheit to an angle of ninety degrees, with a curve having a radius of fifteen inches, for pipes of one inch and less, and fifteen times the diameter of pipe for larger sizes. /. The insulating lining must not soften injuriously at a temperature below^ 212 degrees Fahrenheit and must leave water in which it is boiled practically neutral. g. The insulating lining must be at least one thirty-second of an inch in thickness. The materials of which it is com- posed must be of such a nature as will not have a deteriorat- ing effect on the insulation of the conductor and be suffi- ciently tough and tenacious to withstand the abrasion test of drawing long lengths of conductors in and out of same. h. The insulating lining must no.t be mechanically weak after three days' submersion in water, and when removed from the pipe entire must not absorb more than ten per cent of its weight of water during 100 hours of submersion. /. All elbows or bends must be so made that the con- duit or lining of same will not be injured. The radius of the curve of the inner edge of any elbow must not be less than three and one-half inches. Unlined Metal Conduits. (See Figure i^i.) j. Pipe sizes to run as follows : Trade Size. Approximate Internal Minimum Thickness Inches. Diameter. of Wall. Inches. Inches. % .62 .100 % .82 .105 1 1.04 .125 1^/4 1.38 .135 11/2 1.61 .140 2 2.06 .150 2V2 2.46 .200 3 3.06 .210 31/2 3.54 .220 At no point (except at screw thread) shall the thickness of wall of finislied conduit be less than the minimum specified in last column of above table. k. Pipe to be thoroughly cleaned to remove all scale. 'ib^ MODERN ELECTRICAL CONSTRUCTION. Pipe should be of suffi'ciently true circular section to admit of cutting true,, clean threads, and should be very closely the same in wall thickness at all points with clean square weld. Figure 151. /. Cleaned pipe to be protected against effects of oxida- tion, by baked enamel, zinc or other approved coating which will not soften at ordinary temperatures, and of sufificient weight and toughness to successfully withstand rough usage likely to be received during shipment and installation ; and Figure 152. of sufficient elasticity to prevent flaking when 14 inch con- duit is bent in a curve the inner edge of which has radius of 3J^ inches. in. All elbows or bends must be so made that the con- duit will not be injured. The radius of the curve of the inner edge of any elbow not to be less than 3^ inches. 49 A. Switch and Outlet Boxes. {See Figure 1^2.) p. Must be of pressed steel having a wall thickness not fiTTlNGS, MATERIALS, ETC. 253 less than .081 in. (No. 12 B. & S. gage) or of cast metal having a wall thickness not less than 0.128 in. (No. 8 B. & S. gage.) h. Must be well galvanized, enameled or otherwise prop- erly coated, inside and out, to prevent oxidation. c. Must be so made that all openings not in use will be effectively closed by metal which will afford protection sub- stantially equivalent to the walls of the box. d. Must be plainly marked, where it may readily be seen when installed, with the name or trade mark of the -manufacturer. e. Must be arranged to secure in position the conduit or flexible tubing protecting the wire. This rule will be complied with if the conduit or tubing is firmly secured in position by means of some approved device v/hich may or may not be a part of the box. f. Boxes used with lined conduit must comply with the foregoing requirements, and in addition must have a tough and tenacious insulating lining at least 1-32 inch thick, firmly secured in position. g. Switch and outlet boxes must be so arranged that they can be securely fastened in place independently of the sup- port afforded by the conduit piping, except that when entirely exposed, approved boxes, which are threaded so as to be firmly supported by screwing on to the conduit pipe, may be used. h. Switch boxes must completely enclose the switch on sides and back and must provide a thoroughly substantial support for it. The retaining screws for the box must not be used to secure the switch in position. i. Covers for outlet boxes must be of metal equal in thickness to that specified for the walls of the box, or must be of metal lined with an insulating material not less than 1-32 inch in thickness, firmly and permanently secured to the metal. 254 MODERN ELECTRICAL CONSTRUCTION. SO. Mouldings. (For wiring rules, see No. 24 k to m.) Wooden Mouldings. a. Must have, both outside and inside, at least two coats of waterproof material, or be impregnated with a moisture repellent. h. Must be made in two pieces, a backing and a capping and must afford suitable protection from abrasion. Must be so constructed as to thoroughly encase the wire, be provided with a tongue not less than 1-2 inch in thickness between the conductors, and have exterior walls which under grooves shall not be less than 3-8 inch in thickness, and on the sides not less than 1-4 inch in thickness. It is recommended that only hardwood moulding be used. Metal Mouldings. {For wiring rules, see Nos. 24, k to m, and 25 A.) c. Each length of such moulding must have maker's name or trade mark stamped in the metal, or in some manner per- manently attached thereto, in order that it may be readily identified in the field. The use of paper stickers or tagrs cannot be considered FITTINGS^ MATERIALS, ETC. 255 satisfactory methods of marking-, as they are readily loosened and lost off in ordinary handling of the moulding. d. Must be constructed of iron or steel with backing at least .050 inch in thickness, and with capping not less than .040 inch in thickness, and so constructed that when in place the raceway will be entirely closed; must be thoroughly gal- vanized or coa.ted with an approved rust preventive both inside and out to prevent oxidation. e. Elbows, couplings and all other similar fittings must be constructed of- at least the same thickness and quality of metal as the moulding itself and so designed that they will both electrically and mechanically secure the different sec- tions together and maintain the continuity of the raceway. The interior surfaces must be free from burrs or sharp cor- ners which might cause abrasion of the wire coverings. /. Must at all outlets be so arranged that the conductors cannot come in contact with the edges of the metal, either of capping or backing. Specially designed fittings which will interpose substantial barriers between conductors and the edges of metal are recommended. g. When backing is secured in position by screws or bolts from the inside of the raceway, depressions must be pro- vided to render the heads of the fastenings flush with the moulding. h. Metal mouldings must be used for exposed work only and must be so constructed as to form an open raceway to be closed by the capping or cover after the wires are laid in. 50A. Tubes and Bushings. (See Figure 153.) a. Construction. — Must be made straight and free from checks or rough projections, with ends smooth and rounded to facilitate the drawing in of the wire and prevent abrasion of its covering. b. Material and Test. — Must be made of non-combust- ible insulating material, which, when broken and submerged for 100 hours in pure water at 70 degrees Fahrenheit, will not absorb over one-half of one per cent of its weight. 256 MODERN ELECTRICAL CONSTRUCTION. c. Marking. — Must have the name, initials or trade mark of the manufacturer stamped in the ware. d. Sizes. — Dimensions of walls and heads must be at least as great as those given in the following table : Diameter External Thick- External Length of Diameter. ness of Diameter of Hole. Wall. of Head. Head. Inches. Inches. Inches. Inches. Inches. ^ ^ % it % % i A H V^ Ya 1 ^ lA V2 % ■i !^ 1^ % % lA ,?, IH % 1 lA /2 IM % iy4 m ,^ 2^ % 1% 2A 21* % 1% 2A 3T^r % 2 2M 3A % 2% 3t\ H 311 1 2V2 3U M 4^ 1 An allowance of one-sixty-fourth of an inch for varlgitlon in manufacturing- will be permitted, except in the thickness of the wall. SOB. Cleats. (See Figure 153.) a. Construction. — Must hold the wire firmly in place without injury to its covering. Sharp edges which may cut the wire should be avoided. h. Supports. — Bearing points on the surface must be made by ridges or rings about the holes for supporting screws, in order to avoid cracking and breaking when screwed tight. c. Material and Test. — Must be made of non-combust- ible insulating material, which, when broken and submerged for 100 hours in pure water at 70 degrees Fahrenheit, will not absorb over one-half of one per cent of its weight. d. Marking. — Must have the name, initials or trade mark of the manufacturer stamped in the ware. e. Sizes. — Must conform to the spacings given in the following table : Distance from Wire Distance between Voltage to Surface. Wires. 0-300 % inch. 2% Inches. FITTINGS^ MATERIALS^ ETC. 257 This rule will not be Interpreted to forbid the placing of the neutral of an Edison three-wire system in the center of the three-wire cleat where the difference of potential between the outside wires is not over 300 volts, provided the outside wires are separated two and one-half inches. 50C. Flexible Tubing. {See Figure 154.) a. Must have a sufficiently smooth interior surface to allow the ready introduction of the wire. h. Must be constructed of or treated with materials which will serve as moisture repellents. c. The tube\ must be so designed that it will withstand all the abrasion likely to be met with in practice. d. The linings, if an_v, must not be removable in lengths of over three feet. e. The 1-4 inch tube must be so flexible that it will not crack or break when bent in a circle with 6-inch radius at 50 degrees Fehrenheit (10 degrees Centigrade), and the cov- ering must be thoroughly saturated with a dense moisture- Figure 154. proof compound which will not slide at 150 degrees Fahren- heit (65 degrees Centigrade). Other sizes must be as well made. /. Must not convey fire on the application of a flame from Bunsen burner to the exterior of the tube when held in a vertical position. g. Must be sufficiently tough and tenacious to withstand severe tension without injury; the interior diameter must not be diminished or the tube opened up at any point by the application of a reasonable stretching force. h. Must not close to prevent the insertion of the wire after the tube has been kinked or flattened and straightened out. MODERN ELECTRICAL CONSTRUCTION. 51. Switches. {For installation rules, see Nos. 17 and 22.) General Rules. a. Must, when used for service switches, indicate, on in- spection, whether the current be "on" or "off." h. Must, for constant-current systems, close the main cir- cuit and disconnect the branch wires when turned "off" ; must be so constructed that they shall be automatic in action, not stopping between points when started, and must prevent an arc between the points under all circumstances. They must indicate whether the current be "on" or "off." Knife Switches. {See Figure 155.) Knife switches must be made to comply with the following specifications, except in tliose few cases where peculiar design allows the switch to fulfill the general requirements in some other way, and where it can successfully withstand the test of Section i. In such cases, the switch should be submitted • for special examination before being used. c. Base. — Must be mounted on non-com.bustible, non- absorptive insulating bases, such as slate or porcelain. Bases with an area of over twenty- five square inches must have at least four sup- porting screws. Holes for the supporting screws must be so located or countersunk that there will be at least one-half inch space, meas- ured over the surface, between the head of the screw or washer and the nearest live metal part, and in all cases when between parts of opposite polarity must be countersunk. d. Mounting. — Pieces carrying the con- tact jaws and hinge clips must be secured to the base by at least two screws, or else made with a square shoulder or provided with dowel- pins, to prevent possible turnings, and the nuts or screw heads on the under side of the base must be countersunk not less than one-eighth Fig. 155. FITTINGS^ MATERIALS, ETC. 259 inch and covered with a waterproof compound which will not melt below 150 degrees Fahrenheit. e. Hinges. — Hinges of knife switches must not be used to carry current unless they are equipped with spring washers, held by lock-nuts or pins, or their equivalent, so arranged that a firm and secure connection will be maintained at all posi- tions of the switch blades. Spring- washers must be of sufficient strength to take up any wear in the hinge and maintain a good contact at all times. /. Metal. — All switches must have ample metal for stiffness and to prevent rise in temperature of any part of over fifty degrees Fahrenheit at full load, the contacts being ar- ranged so that a thoroughly good bearing at every point is obtained with contact surfaces advised for pure copper blades of about one square inch for each seventy-five amperes ; the whole device must be mechanically well made throughout. g. Cross-Bars. — All cross-bars less than three inches in length must be made of insulating material. Bars of three inches and over, which are made of metal, to insure greater mechanical strength, must be sufficiently separated from the jaws of the switch to prevent arcs following from the con- tacts to the bar on the opening of the switch under any cir- cumstances. Metal bars should preferably be covered with insulating material. To prevent possible turning or twisting the cross-bar must be secured to each blade by two screws, or the joints made with square shoulders or provided with dowel-pins. h. Connections. — Switches for currents of over thirty amperes must be equipped with lugs, firmly screwed or bolted to the switch, and into which the conducting wires shall be soldered. For the smaller sized switches simple clamps can be employed, provided they are heavy enough to stand considerable hard usage. "Wliere lugs are not provided, a rugged double V groove clamp is advised. A set screw gives a contact at only one point, is more likely to become loosened, and is almost sure to cut into the wire. For the smaller sizes, a screw and washer connection with turned-up lugs on the switch terminal gives a satisfactory contact. 260 MODERN ELECTRICAL CONSTRUCTION. i. Test. — Must operate successfully at 50 per cent over- load in amperes and 25 per cent excess voltage, under the most severe conditions with which they are liable to meet in practice. This test is designed to give a reasonable margin between the ordinary rating of the switch and the brealcing-down point, thus securing a switcli which can always safely handle its nor- mal load. Moreover, there is enough leeway so that a moderate amount of overloading would not injure the switch. j. Marking. — Must be plainly marked where it will be visible, when the switch is installed, with the name of the maker and the current and voltage for which the switch is designed. Switches designed for use on Edison three-wire systems must be marked with both voltages, that is the voltage between the outside wires and the neutral, and also that between the outside wires, followed by the ampere rating and the words "three wire." (For example, "125-250 v. 30 a, three-wire.") k. Spacings. — Spacings must be at least as great as those given in the following table. The spacings specified are correct for switches to be used on direct-current systems, and can therefore be safely followed in devices designed for alter- nating currents. 125 volts or less: Minimum Separation of Minimum Nearest Metal Parts of Break- Opposite Polarity. Distance. For Switchboards and Panel Boards — 10 amperes or less % inch. 11-.30 amperes 1 " 31-50 amperes 1 14 " For individual Switches — 10 amperes or less 1 inch. 11-30 " 114 " 31-100 " 11/2 " 101-300 " 214 " 301-600 " 2% " 601-1000 " 3 126 to 250 volts: For all Switches — 10 amperes or less 1% inch. 11-30 amperes 1 % 31-100 " 21/4 101-300 " 21/^ 301-600 " 234 601-1000 " 3 V?. inch. % 1 % inch. 1 1V4 " 2 2% 2% m inch. IV?. 2 " 2% " 21/2 " FITTINGS^ MATERIALS^ ETC. 261 For 100 ampere switches and larger, the above spacings for 250 volts direct current are also approved for 500 volts alternating current.. Switches with these spacings intended for use on alternating-current systems with voltage above 250 volts must be stamped "250-volt D. C," followed by the alter- nating current voltage for which they are designed, and the letters "A. C." For all Switches — 10 amperes or less S^/^ inch. 3 inch. 11-35 amperes 4 " 3% " 36-100 " 41^" 4 Auxiliary breaks or the equivalent are recommended for switches designed for over 300 volts and less than 100 amperes, and will be required on switches designed for use in breaking currents greater than 100 amperes at a pressure of more than 300 volts. For three-wire Edison systems the separations and break distances for plain three-pole knife switches must not be less than those required in the above table for switches designed for the voltage between the neutral and outside wires. Snap Switches. {See Figures 156 and 157.) Flush, push-button, door, fixture, and other snap switches used on constant-potential systems, must be constructed in accordance with the following specifications. /. Base. — Current-carrying parts must be mounted on non-combustible, non-absorptive insulating bases, such as slate Figure 156. or porcelain, and the holes for supporting screws should be countersunk not less than one-eighth of an inch. There must in no case be less than three sixty-fourths of an inch space between supporting screws and current-carrying parts. Sub-bases of non-combustible, non-absorptive insulating 262 MODERN ELECTKICAL CONSTRUCTION. material, which will separate the wires at least one-half of an inch from the surface wired over, must be furnished with all snap switches used in exposed or moulding work. m. Mounting. — Pieces carrying contact jaws must be secured to the base by at least two screws, or else made with a square shoulder, or provided with dowel-pins or otherwise arranged, to prevent possible turnings ; and the nuts or screw heads on the under side of the base must be countersunk not less than one-eighth inch, and covered with a waterproof compound which will not melt below 150 degrees Fahrenheit. n. Metal. — All switches must have ample metal for stiffness and to prevent rise in temperature of any part of over Figure 157. 50 degrees Fahrenheit at full load, the contacts being arranged so that a thoroughly good bearing at every point is obtained. The whole device must be mechanically well made throughout. In order to meet the above requirements on temperature rise without causing excessive friction and wear on current- carrying parts, contact surfaces of from 0.1 to 0.15 square inch for each 10 amperes will be required, depending upon the metal used and the form of construction adopted. 0. Insulating Material. — Any material used for insu- lating current-carrying parts m.ust retain its insulating and mechanical strength when subject to continued use, and must not soften at a temperature of 212 degrees Fahrenheit. It must also be non-absorptive. p. Binding Posts. — Binding posts must be substantially FITTINGS^ MATERIALS^ ETC. 263 made, and the screws must be of such size that the threads will not strip when set up tight. A set-screw is likely to become loosened and is almost sure to cut into the wire. A binding- screw, under the head of which the wire may be clamped, and a terminal plate pro- vided with upturned lugs or some other equivalent arrange- ment, afford reliable contact. After July 1, 1908, switches with the set-screw form of contact will not be approved. q. Covers. — Covers made of ' conducting material, ex- cept face plates for flush switches, must be lined on sides and top with insulating, tough and tenacious material at least one- thirty-second inch in thickness, firmly secured so that it will not fall out with ordinary handling. The side lining must ex- tend slightly beyond the lower edge of the cover. r. Handle or Button. — The handle or button or any exposed parts must not be in electrical connection with the circuit. s. Test. — Must "make" and "break" with a quick snap, and must not stop when motion has once been imparted by the button or handle. Must operate successfully at 50 per cent over-load in amperes and at 125 volt direct current, for all 125 volt or less switches, and at 250 volts direct current, for all 126 to 250 volt switches under the most severe conditions which they are liable to meet in practice. When slowly turned "on and off" at the rate of about two or three times per minute, while carrying the rated current at rated voltage, must "make and break" the circuit six thousand times before failing. t. Marking. — Must be plainly marked, where it may be readily seen after the device is installed, with the name or trade mark of the maker and the current and voltage for which the switch is designed. On flush switches these markings may be placed on the back of the face plate or on the sub-plate. On other types they must be placed on the front of the cap, cover, or plate. Switches which indicate whether the current is "on" or "off" are recommended. 264 MODERN ELECTEICAIi CONSTEUCTION. 52. Cut-Outs and Circuit-Breakers. {^See Figu7'e i^8.) {For installation rules, see Nos. ly and 21.) These requirements do not apply to rosettes, attachment plugs, car lighting cut-outs and protective devices for signal- ing systems. General Rules. a. Must be supported on bases of non-combustible, non- absorptive insulating material. b. Cut-outs must be of plug or cartridge type, when not arranged in approved cabinets, so as to obviate any danger of the melted fuse metal coming in contact with any substance which might be ignited thereby. c. Cut-outs must operate successfully on short-circuits, ■ under the most severe conditions with which they are liable to jingle Pole. Figure 158. meet in practice, at 25 per cent above their rate of voltage and the fuses rated at 50 per cent above the current for which the cut-out is designed, and for enclosed fuse cut-outs with the largest fuses for which the cut-cut is designed. With link fuse cut-outs there is always the possibility of a larger fuse being put into the cut-out than it was designed FITTINGS, MATERIALS, ETC. 2b5 for, which is not true of enclosed fuse cut-outs classified as required under No. 52 q. Again, the voltage in most plants can, under some conditions, rise considerably above the nor- mal. The need of some margin, as a factor of safety to pre- vent the cut-outs from being ruined in ordinary service, is therefore evident. The most severe service which can be required of a cut-out in practice is to open a "dead short-circuit" with only one fuse blowing, and it is with these conditions that all tests should be made. (See Section j.) d. Circuit-breakers must operate successfully on short-cir- cuits, under the most severe conditions with which they are Hable to meet in practice, at 25 per cent above their rated voltage and with the circuit-breaker set at the highest pos- sible opening point. For the sarse reason as in Section c. e. Must be plainly marked where it will always be visible, with the name of the maker, and current and voltage for which the devi-ce is designed. Link-Fuse Cut-Outs. (See Figure 159.) (Cut-outs of porcelain are not approved for link fuses.) The following rules are Intended to cover open link fuses mounted on slate or marble bases, including switchboards, tablet-boards, and single fuse-blocks. They do not apply to fuses mounted on porcelain bases, to the ordinary porcelain cut-out blocks, enclosed fuses, or any special or covered type of fuse. When tablet-boards or single fuse-blocks with such open link fuses on them are used in general wiring, they must be enclosed in cabinet boxes made to meet the requirements of No. 54. This is necessary, because a severe flash may occur when such fuses melt, so that they would be dangerous if exposed in the neighborhood of any combustible material. /. Base. — Must be mounted on slate or marble bases. Bases with an area of over twenty-five square inches must have at least four supporting screws. Holes for supporting screws must be kept outside of the area included by the out- side edges of the fuse-block terminals and must be so located or countersunk that there will be at least one-half an inch space, measured over the surface, between the head of the screw or washer and the nearest live part. g. Mounting. — Nuts or screw-heads on the under side -O" MODERN ELECTRICAL CONSTRUCTION. of the base must be countersunk not less than one-eighth inch, and covered with a waterproof compound which will not melt below 150 degrees Fahrenheit. Figure 159 Figure 160; h. Metal. — All fuse-block terminals must have ample metal for stiffness and to prevent rise in temperature of any part of over 50 degrees Fahrenheit at full load. Terminals, as far as practicable, should be made of compact form instead of being rolled out in thin strips; and sharp edges or thin pro- jecting pieces as on winged thumb nuts and the like should be avoided. Thin metal, sharp edges and projecting pieces are much more likely to cause an arc to start than a more solid mass_ of metal. It is a good plan to round all corners of the terminals and to chamfer the edges. i. Connections. — Clamps for connecting the wires to the fuse-block terminals must be of solid, rugged construction, so as to insure a thoroughly good connection and to withstand considerable hard usage. For fuses rated at over thirty amperes tugs firmly screwed or bolted to the terminals and into which the conducting wires are soldered must be used. See note under No. 51 h. /. Test. — Must operate successfully when blowing only one fuse at a time on short-circuits with fuses rated at 50 per cent above and with a voltage 25 per cent above the current and voltage for which the cut-out is designed. h. Marking.— Must be plainly marked, where it will be FITTINGS, MATEEIALS, ETC. ^Ci visible when the cut-off block is installed, with the name of the maker and the current and' the voltage for which the block is designed. /. Spacings. — Spacings must be at least as great as those given in the following table, which applies only to plain, open link-fuses mounted on slate or marble bases. The spac- ings given are correct for fuse-blocks to be used on direct- current systems, and can therefore be safely followed in devices designed for alternating currents. If the copper fuse-tips over- hang the edges of the fuse-block terminals, the spacings should be measured between the nearest edges of the tips. Minimum Separation of Minimum Nearest Metal Parts of Break- 125 volts or less: Opposite Polarity. Distance. 10 amperes or less % inch. % inch. 11-100 amperes 1 " % 101-103 " 1 " 1 301-1000 " 114= " 1^/4 " 126 to 250 volts: 10 amperes or less \'V2 inch. 1^4 inch. 11-100 amperes 1% " IV4. " 101-300 " 2 " 11/^ " 301-1000 " 2l^ " 2 A space must be maintained between fuse terminals of the same polarity of at least one-half inch for voltages up to 12 5 and of at least three-quarter inch for voltages from 126 to 250. This is the miniinum distance allowable, and greater separa- tion should be provided when practicable. For 250 volt boards or blocks with the ordinary front-con- nected terminals, except where these have a mass of compact form, equivalent to the back-connected terminals usually found in switchboard work, a substantial barrier of insulating ma- terial, not less than one-eighth of an inch in thickness, must be placed in the "break-gap" — this barrier to extend out from the base at least one-eighth of an inch farther than any bare live part of the fuse-block terminal, including binding screws, nuts and the like. (Figure 160.) For three-wire systems cut-outs must have the break-dis- tance required for circuits of the potential of the outside wires. Enclosed-Fuse Cut-Outs — Plug and Cartridge Type. (See Figure 161.) m. Base. — Must be made of non-combustible, non- absorptive insulating material. Blocks with an area of over MODERN ELECTRICAL CONSTRUCTION. twenty-five square inches must have at least four supporting screws. Holes for supporting screws must be so located or countersunk that there will be at least one-half of an inch space, measured over the surface, between the screw-head or washer and the nearest live metal part, and in all cases when between parts of opposite polarity must be countersunk. n. Mountings. — Nuts or screw-heads on the under side of the base must be countersunk at least one-eighth of an inch and covered with a waterproof compound which will not melt below 150 degrees Fahrenheit. 0. Terminals. — Terminals must be of either the Edi- son plug, spring clip or knife blade type, of approved design, to take the corresponding standard enclosed fuses. They must be secured to the base by two screws or the equivalent, so as to prevent them from turning, and must be so made as to secure a thoroughly good contact with the fuse. End stops I Figure 161. must be provided to insure the proper location of the cartridge fuse in the cut-out. p. Connections. — Clamps for connecting wires to the terminals must be of a design which will insure a thoroughly good connection, and must be sufficiently strong and heavy to withstand considerable hard usage. For fuses rated to carry over thirty amperes, lugs firmly screwed or bolted to the terminals and into which the connecting wires shall be soldered must be used. q. Classification. — Must be classified as regards both current and voltage as given in the following table, and must be so designed that the bases of one class' cannot be used with fuses of another class rated for a higher current or voltage. fittings, matekials^ etc. 269 0-250 Volts. 251-600 Volts. 0- 30 amperes. 0- 30 amperes, 31- 60 " 31- 60 61-100 " 61-100 101-200' " 101-200 201-400 " 201-400 401-600 r. Design. — Must be of such a design that it will not be easy to form accidental short-circuits across live metal parts of opposite polarity on the block or on the fuses in the block. .?. Marking. — Must be marked, where it will be plainly visible when the block is installed, with the name of the maker and the voltage and range of current for which it is designed. 53. Fuses. {For installation rules, see Nos. ly and 21.) Link Fuses. a. Terminals. — Must have contact surfaces or tips of harder metal, having perfect electrical connections with the fusible part of the strip. The use of the hard metal tip is to afford a strong- mechani- cal bearing- for the screws, clamps, or other devices provided for holding- the fuse. b. Rating. — Must be stamped with about 80 per cent of the maximum current which they can carry indefinitely, thus allowing about 25 per cent overload before the fuse melts. With naked open fuses, of ordinary shapes and with not over 500 amperes capacit3^ the minimum current whicli will melt them in ahout five minutes may be safely taken as the melting point, as the fuse practically reaches its maximum temperature in this time. With larg-er fuses a longer time is necessary. This data are given to facilitate testing. c. Marking. — Fuse terminals must be stamped with the maker's name or initials, or with some known trade mark. Enclosed Fuses — Plug and Cartridge Type. (See Figure 161 ) These requirements do not apply to fuses for rosettes, at- tachment plugs, car lighting, cut-outs and protective devices for signaling systems. 270 MODERN ELECTRICAL CONSTRUCTION. d. Construction. — The fuse plug or cartridge must bel sufficiently dust-tight so that lint and dust cannot collect | around the fusible wire and become ignited when the fuse is blown. The fusible wire must be attached to the plug or cartridge : terminals in such a way as to secure a thoroughly good con- nection and to make it difficult for it to be replaced when melted. e. Classification. — Must be classified to correspond with the different classes of cut-out blocks, and must be so designed that it will be impossible to put any fuse of a given class into a cut-out block which is designed for a current or voltage lower than that of the class to which the fuse belongs. /. Terminals. — The fuse terminals must be sufficiently heavy to ensure mechanical strength and rigidity. The styles of terminals must be as follows : 0-250 Volts. r [a, spring clip r. ars K ) A Cartridge fuse | to ■< terminals. 0-30 Amps. J. A-\ ^„ i + ^^v ^ E? ) &, Edison j I (ferrule contact) ( fit ( pi^^ casings. \ B Approved plugs for Edison cut-outs. ( a, spring clip Cartridge fuse | to •< >. terminals. ,„ 1 ^ ^v h L? ) b, Edison plug (ferrule conta,ct) | fit I casings. 61-100 '' ^ 201-400 " r Cartridge fuse (knife blade contact). 400-600 " ) 251-600 Volts. 0-30 Amps. I Cartridge fuse (ferrule contact). 61-100 " ) 101-200 " ^Cartridge fuse (knife contact). 201-400 " ) g. Dimensions. — Cartridge enclosed fuses and corre- sponding cut-out blocks must conform to the dimensions given in the table attached. FITTINGS, MATEEIALS, ETC. 271 h. Rating. — Fuses must be so constructed that with the surrounding atmosphere at a temperature of 75 degrees I Fahrenheit (24 degrees Centigrade) they will carry indefinitely \ a current 10 per cent, greater than that at which they are rated j: and at a current 25 per cent greater than the rating they will ; open the circuit without reaching a temperature which will in- ' jure the fuse tube or terminals of the fuse block. With a cur- I rent 50 per cent greater than the rating and at room tempera- I ture of 75 degrees Fahrenheit (24 degrees Centigrade), the j ftises starting cold, must blow within the time specified below : 0- 30 amperes, 30 seconds. 31- 60 " 1 minute. 61-100 " - 2 minutes. 101-200 " 4 201-400 " 8 401-600 " 10 »', Marking. — Must be marked, where it will be plainly visible, with the name or trade-mark of the maker, the volt- age and current for which the fuse is designed, and the words "National Electrical Code Standard." Each fuse must have a label, the color of which must be green for 250-volt fuses and red for 600-volt fuses. It will be satisfactory to abbreviate the above designation to "N. E. Code St'd" where space is necessarily limited. /. Temperature Rise. — The temperature of the ex- terior of the fuse enclosure must not rise more than 125 degrees Fahrenheit (70 degrees Centigrade) above that of the surrounding air when the fuse is carrying the current for which it is rated. k. Test. — Must not hold an arc or throw out melted metal or sufficient flame to ignite easily inflammable material oil or near the cut-out when only one fuse is blown at a time on a short circuit on a system of the voltage for which the fuse is rated. The normal capacity of the system must be in excess of the load on it just previous to the test by at least five times the rated capacity of the fuse under test. The resistance of the circuit up to the cut-out terminals must be such that the impressed voltage at the terminals will be decreased not more than 1 per cent when a current of ICO amperes is passed between them. MODERN ELECTRICAL CONSTRUCTION. TABLE OF DIMENSIONS OF THE STANDARD CARTRIDGE Forml. CARTRIDGE FUSE-Ferrule Contact. Rated Capacity. Amperes. A B C Voltage. Length over Terminals. Inches. Distance between Contact Clips Inches. Width of Contact Clips. Inches. 0-250 0-30 31-60 S 2 £ 3 1 1% 61-100 101-200 201-400 401-600 ^ 5% ° 8% ^ 10% 4 6 1^ 251-600 0-30 31-60 E. 5 SL 5^2 4 4^2 % % 61-100 101-200 201-400 ^ 7% E 9% SL 11% 6 7 8 % FITTINGS^ MATERIALS^ ETC. NATIONAL ELECTRICAL CODE ENCLOSED FUSE Form 2. CARTRIDGE FUSE— Knife Blade Contact. D E F G Diameter of Ferrules or Thiclvness of Terminal Blades. Inches. Min. Length of Ferrules or of Terminal Blades outside of Tube. Inches. Dia. of Tube. Inches. Width of Terminal Blades. Inches. Eated Capacity. Amperes. 3 0-30 31-60 1 1% 1% 2M 1 1% 2ys 5£ -^ 61-100 101-200 201-400 401-600 it % % i'^ 1 0-30 31-60 1 1% 1% iM 21/2 ill 61-100 101-200 201-400 MODERN ELECTEICAL CONSTRUCTION. For convenience a current of different value may be used, in which case the per cent drop in voltage allowable would vary in, direct proportion to the difference in current used. The above requirement regarding the capacity of the test- ing circuit is to guard against malcing the test on a system Three- Wire Mains Figure 182. of so small capacity that the conditions would be sufficiently favorable to allow really poor fuses to stand the test accept- ably. On the other hand, it must be remembered that if the test is made on a system of very large capacity, and especi- ally if there is but little resistance between the generators and fuse, the conditions may be more severe than are liable to be met with in practice outside of the large power stations, the result being that fuses entirely safe for general use may be rejected, if such test is insisted upon. 53A. Tablet and Panel Boards. (See Figure 162.) FITTINGS, MATERIALS, ETC. The following minimum distance between bare live metal parts (bus-bars, etc.) must be maintained: Between parts of opposite polarity Between parts of except at switclies and link fuses. same polarity. When mounted on When held free At link the same surface. in the air. fuses. 0-125 volts % inch. i/^ inch. 1/2 inch. 126-250 volts IV4. inch. % inch. % inch. At switches or enclosed fuses, parts of the same polarity may be placed as close together as convenience in handling will allow. It should be noted that the above distances are the mini- mum allowable, and it is urged that greater distances be adopted wherever the conditions will permit. The spacings given in the first column apply to the branch conductors where enclosed fuses are used. Where link fuses or* knife switches are used, the spacings must be at least as great as those required by Nos. 51 and 52. The spacings given in the second column apply to the dis- tance between the raised main bars and between these bars and the branch bars over which they pass. The spacings given in the third column are intended to prevent the meltingi of a link fuse by the blowing of an ad- jacent fuse of the same polarity. 54. Cut-Out Cabinets. a. Material. — Cabinets must be substantially constructed of non-com- bustible, non-absorptive material, or of wood. When wood is used the inside of the cabinet must be completely Hned with a non-combustible insulating ma- terial. Slate or marble at least one- quarter inch in thickness is strongly recommended for such lining, but, ex- cept with metal conduit systems, asbes- tos board at least one-eighth inch in thickness may be used in dry places if firmly secured by shellac and tacks. With metal conduit systems the lin- ing of either the box or the gutter must be one-sixteenth inch galvanized, painted or enameled steel, or, preferably, one- quarter inch slate or marble. (Figure 163.) 276 MODERN ELECTKICAL CONSTRUCTION. The object of the lining- of such cut-out cabinets or gutters i^ to render the same approximately fireproof in case of short circuit after the wires leave the protecting metal conduits. Two thicknesses of 1-32 inch steel may be used instead of one of 1-16 inch. With wood cabinets the wood should be thoroughly filled and painted before the lining is put in place. b. Door. — The door must close against a rabbet, so as to be perfectly dust-tight. Strong hinges and a strong hook or catch are required. Glass doors must be glazed with heavy glass, not less than ^ inch in thickness, and panes should not exceed 300 square inches in area. A space of at least two inches must be allowed between the fuses and the door. This is necessary to prevent cracking or breaking by the severe blow and intense heat which may be produced under some conditions. A cabinet is of little use unless the door is kept tightly closed, and especial attention is therefore called to the im- portance of having a strong and reliable catch or other fast- ening. A spring catch is advised if a good one can be ob- tained, but most of those sold for use on cupboards, etc., are so small that they fail to catch when the door shrinks a little, or are so weak that they soon give out. It is advised that the bottoms of cabinets be given a de- cided slant to prevent their use as a shelf, as well as the accumulation of dust, etc. c. Bushings. — Bushings through which wires enter must fit tightly the holes in the box, and must be of approved j construction. The wires should completely fill the holes in the | bushings, using tape to build up the wire, if necessary, so asj to keep out the dust. Rule 54A. Rosettes. (See Figure 164.) Ceiling rosettes, both fused and fuseless, must be con- structed in accordance with the following specifications: a. Base. — Current-carrying parts must be mounted on I non-combustible, non-absorptive insulating bases. There I should be no openings through the rosette base except those j for the supporting screws and in the concealed t3^pe for the \ conductors also, and these openings should not be made any larger than necessary. There must be at least one-quarter inch space, measured FITTINGS^ MATERIALS, ETC. 2,11 over the surface, between supporting screws and current- carrying parts. The supporting screws must be so located or countersunk that the flexible cord cannot come in contact with them. Bases for the knob and cleat type must have at least two holes for supporting screws ; must be high enough to keep the wires and terminals at least one-half inch from the surface Figure 164. to which the rosette is attached, and must have a porcelain lug under each terminal to prevent the rosette from being placed over projections which would reduce the separation to less than one-half inch. Bases for the moulding and conduit box types must be high enough to keep the wires and terminals at least three-eighths inch from the surface wired over. b. Mounting. — Contact pieces and terminals must be secured in position by at least two screws, or made with a square shoulder, or otherwise arranged to prevent turning. The nuts or screw heads on the under side of the base must be countersunk not less than one-eighth inch and covered with a waterproof compound which will not melt below 150 degrees Fahrenheit. c. Terminals. — Line terminal plates must be at least .07 inch in thickness, and terminal screws must not be smaller than No. 6 standard screws with about 32 threads per inch. Terminal plates for the flexible cord and for fuses must be at least .06 inch in thickness. The connection to these plates shall be by binding screws not smaller than No. 5 278 MODERN ELECTRICAL CONSTRUCTION. Standard screw with about 40 threads per inch. At aH binding screws for line wires and for flexible cord, up-turned higs, or some equivalent arrangement, must be provided which v/ill secure the wires being held under the screw heads. d. Cord Inlet, — The diameter of the cord inlet hole should measure 13/32 inch in order that standard portable cord may be used. e. Knot Space. — Ample space must be provided for a substantial knot tied in the cord as a whole. All parts of the rosette upon which the knot is likely to bear must be smoolh and well rounded. f. Cover. — When the rosette is made in two parts the cover must be secured to the base so that it will not work loose. In fused rosettes, the cover must fit closely over the base so as to prevent the accumulation of dust or dirt on the inside, and also to prevent any flash or melted metal from being thrown out when the fuses melt. g. Markings. — Must be plainly marked where it may readily be seen after the rosette has been installed, with the name or trade mark of the manufacturer, and the rating in amperes and volts. Fuseless rosettes may be rated 3 amperes, 250 volts ; fused rosettes, with link fuses, not over 2 amperes, 125 volts. h. Test. — Fused rosettes must have a fuse in each pole and must operate successfully when short-circuited on the volt- age for which they are designed, the test being made with the two fuses in circuit. NOTE. — When link fuses are used the test shall be made with fuse wire which melts at about 7 amperes in one inch lengths. The larger fuse is specified for the test in order to more nearly approximate the severe conditions obtained when only one 2-ampere fuse (the rating of the rosette) is blown at a time. Fused rosettes equipped with enclosed fuses are much preferable to the link fuse rosettes. 55. Sockets. (See Figure 165.) (For installation rules, see No. 2y.) FITTINGS^ MATERIALS, ETC. ^79 Sockets of all kinds, including- wall receptacles, must be constructed in accordance with the following: specifications: a. Standard Sizes. — The standard lamp socket must be suitable for use on any voltage not exceeding 250 and with any size lamp up to 50 candle-power. For lamps larger than 50 candle-power a standard keyless socket may be used, or if a key is required a special socket designed for the current to be used must be made. Any special sockets must follow the general spirit of these specifications. h. Marking. — All sockets must be marked with the manufacturer's name or trade-mark. The standard key socket must also be plainly marked 250 v. 50 c. p. Receptacles, keyless sockets and special sockets must be marked with the current and voltage for which they are designed. c. Shell. — Metal used for shells must be moderately hard, but not hard enough to be brittle or so soft as to be Figure 165. easily dented or knocked out of shape. Brass shells must be at least thirteen one-thousandths of an inch in thickness, and shells of any other material must be thick enough to give the same stiffness and strength as the required thickness of brass. d. Lining. — The inside of the shells must be lined with insulating material, which must absolutely prevent the shell from becoming a part of the circuit, even though the wires inside the socket should start from their position under the binding screws. The material used for lining must be at least one thirty- second of an inch in thickness and must be tough and tenacious. It must not be injuriously affected by the heat from the largest lamp permitted in the socket, and must leave 280 MODERN ELECTRICAL CONSTRUCTION. v/ater in which it is boiled practically neutral. It must be so firmly secured to the shell that it will not fall out with ordinary handling of the socket. It is preferable to have the lining in one piece. The cap must also be lined, and this lining must comply with the requirements for sliell linings. The shell lining- should extend beyond the shell far enough so that no part of the lamp base is exposed when a lamp is in the socket. The standard Edison lamp base measures ^| inch, in a vertical plane from the bottom of the center contact to the upper edge of the screw shell. In sockets and receptacles of standard forms a ring of any material inserted between an outer metal shell of the device and the inner screw shell for insulating purposes and separable from the device as a whole is considered an un- desirable form of construction. This does not apply to the use of rings in lamp clusters or in devices where the outer shell is of porcelain, where such rings serve to hold the several porcelain parts together, and are thus a necessary part of the whole structure of the device. e. Cap. — Caps, when of sheet brass, must be at least thirteen one-thousandths of an inch in thickness, and when cast or made of other metals must be of equivalent strength. The inlet piece, except for special sockets, must be tapped with a standard one-eighth-inch pipe thread. It must contain sufficient metal for a full, strong thread, and when not in one piece with the cap must be joined to it in such a way as to give the strength of a single piece. There must be sufficient room in the cap to enable the ordinary wireman to easily and quickly make a knot in the coird and to push it into place in the cap without crowding. All parts of the cap upon which the knot is likely to bear must be smooth and well insulated. The cap lining called for in the note to Section d will pro- vide a sufficiently smooth and well-insulated surface for the knot to bear upon. Sockets with an outlet threaded for three-eighths inch pipe will, of course, be approved where circumstances demand their use. This size outlet is necessary with most stiff pendants and for the proper use of reinforced flexible cord, as explained in the note to No. 28 (L. f. Frame and Screws, — The frame which holds the FITTINGS, MATERIALS, ETC. 281 moving parts must be sufficiently heavy to give ample strength and stiffness. Brass pieces containing screw threads must be at least six one-hundredths of an inch in thickness. Binding post screws must not be smaller than No. 5 stand- ard screw with about 40 threads per inch. g. Spacing. — Points of opposite polarity must every- where be kept not less than three sixty-fourths of an inch apart, unless separated by a reliable insulation. h. Connections. — The connecting points for the flex- ible cord must be made to very securely grip a No. 16 or 18 B. & S. gage conductor. A turned-up lug, arranged so that the cord may be gripped between the screw and the lug in such a way that it cannot possibly come out, is strongly advised. /. Lamp Holder. — The socket must firmly hold the Ismp in place so that it cannot be easily jarred out, and must provide a contact good enough to prevent undue heating with the maximum current allowed. The holding pieces, springs, and the like, if a part of the circuit, must not be sufficiently exposed to allow them to be brought in contact with anything outside of the lamp and socket. ;. Base.— With the exception of the lining all parts of insulating material inside the shell must be made of por- celain. k. Key. — The socket key-handle must be of such a material that it will not soften from the heat of a fifty candle- power lamp hanging downwards from the socket in air at 70 degrees Fahrenheit, and must be securely, but not necessarily rigidly, attached to the metal spindle wjiich it is designed to turn. /. Sealing. — All screws in porcelain pieces, which can be firmly sealed in place, must be so sealed by a waterproof compound which will not melt below 200 degrees Fahrenheit. m. Putting Together. — The socket as a whole must be so put together that it will not rattle to pieces. Bayonet joints or an equivalent are recommended. n. Test. — The socket, when slowly turned "on and off" at the rate of about two or three times per minute, 282 MODERN ELECTRICAL CONSTRUCTION. while carrying a load of one ampere at 250 volts, must "make and break" the circuit 6,000' times before failing. o. Keyless Sockets. — Keyless sockets of all kinds must comply with the requirements for key sockets as far as they apply. p. Sockets of Insulating Material. — Sockets made of porcelain or other insulating material must conform to the above requirements as far as they apply, and all parts must be strong enough to withstand a moderate amount of hard usage without breaking. Porcelain shell sockets being- subject to breakage, and con- stituting' a hazard when broken, will not be accepted for use in places where they would be exposed to hard usage. q. Inlet Bushing. — When the socket is not attached to a fixture, the threaded inlet must be provided with a strong insulating bushing having a smooth hole at least nine thirty- seconds of an inch in diameter. The edges of the bushing must be rounded and all inside fins removed, so that in no place will the cord be subjected to the cutting or wearing action of a sharp edge. Bushing's for sockets having- an outlet threaded for three- eighths-inch pipe should have a hole thirteen thirty-seconds of an inch in diameter, so that they will accommodate approved reinforced flexible cord. 56. Hanger-Boards. (See Figure i66.) a. Hanger-boards must be so constructed that all wires and current-carrying devices thereon will be exposed to view Fig-ure 166. and thoroughly insulated by being mounted on a non-com- bustible, non-absorptive insulating substance. All switches FITTINGS^ MATERIALS^ ETC. 283 attached to the same must be so constructed that they shall be automatic in their action, cutting off both poles to the lamp, not stopping between points when started and preventing an arc between points under all circumstances. 57. Arc Lamps. (See Figure 167.) (For installation rules, see Nos. ig and 2g.) a. Must be provided with reliable stops to prevent car- bons from falling out in case the lamps become loose. h. All exposed parts must be carefully insulated from the circuit. c. Must, for constant-current systems, be provided with an approved hand switch, and an automatic switch that will shunt the current around the carbons, should they fail to feed properly. The hand switch to be approved, if placed anywhere except on the lamp itself, must comply with requirements for switches on hanger-boards as laid down in No. 56. 58. Spark Arresters. (See Figure 167.) (For installation rules, see Nos. 19 c and 2g c.) a. Spark arresters must so close the upper orifice of the globe that it will be impossible for any sparks, thrown out by the carbons, to escape. Figure 167 59. Insulating Joints. (See No. 26 a.) a. Must be entirely made of material that will resist the action of illuminating gases, and will not give way or soften under the heat of an ordinary gas flame or leak under a mod- erate pressure. Must be so arranged that a deposit of mois- ture will not destroy the insulating effect; must show a 284 MODEIIX ELECTRICAL CONSTRUCTION. dielectric strength between gas-pipe attachments sufficient to resist throughout five minutes the application of an electro- motive force of 4,000 volts ; and must be sufficiently strong to resist the strain to which they are liable to be subjected during installation. b. Insulating joints having soft rubber in their construc- tion will not be approved. 60. Rheostats. (For installation rules, see Nos. 4 a and 8 c.) a. Materials. — Must be made entirely of non-com- bustible materials, except such minor parts as handles, magnet insulation, etc. All segments, lever arms, etc., must be mounted on non- combustible, non-absorptive insulating material. Rheostats used in dusty or linty places or where exposed to fiying-s of combustible material must be so constructed that even if the resistive conductor be fused by excessive current the arc or any attendant flame will be quickly and safely extinguished. Rheostats used in places where the above conditions do not exist may be of any approved type. b. Construction. — ]\Iust be so constructed that when mounted on a plane surface the casing will make contact with such surface only at the points of support. An air space of at least ^ inch between the rheostat casing and the support- ing surface will be required. The construction throughout must be heavy, rugged and thoroughly workmanlike. c. Connections. — Clamps for connecting wires to the terminals must be of a design which will ensure a thoroughly good connection, and must be sufficiently strong and heavy to withstand considerable hard usage. For currents above fifty amperes, lugs firmly screwed or bolted to the terminals, and into which the connecting wires shall be soldered, must be used. Clamps or lug's will not be required where leads designed for soldered connections are provided. d. Marking. — Must be plainly marked, where it may be readily seen after the device is installed, with the rating and the name of the maker ; and the terminals of motor-starting FITTINGS^ MATERIALS, ETC. 285 rheostats must be marked to indicate to what part of the circuit each is to be connected, as "line," "armature," and "field." e. Contacts. — The design of the fixed and movable contacts and the resistance in each section must be such as to secure the least tendency toward arcing and roughening of the contacts, even with careless handling or the presence of dirt. In motor-starting rheostats, the contact at which the cir- cuit is broken by the lever arm when moving from the running to the starting position must be so designed that there will be no detrimental arcing. The final contact, if any, on which the arm is brought to rest in the starting position must have no electrical connection. Experience has shown that sharp edg"es and segments of thin material help to maintain an arc, and it is recommended that these be avoided. Seg-ments of heavy construction have a considerable cooling effect on the arc, and rounded corners tend to spread it out and thus dissipate it. It is recommended that • the circuit-breaking- contacts be so constructed as to "break" with a quick snap, independently of the slowness of movement of the operator's hand, or that a magnetic blowout or equivalent device be used. For dial type rheostats the movable contact should be flexible in a plane at right angles to the plane of its movement, and f'br medium and larger sizes the stationary contacts should be readily renewable. /. No-voltage release. — Motor-starting rheostats must be so designed that the contact arm cannot be left on inter- mediate segments, and must be provided wi.th an automatic device which will interrupt the supply circuit before the speed of the motor falls to less than one-third of its normal value. g. Overload-release. — Overload-release devices which are inoperative during the process of starting a motor will not be approved, unless other circuit-breakers or fuses are installed in connection with them. If, for instance, the overload-release device simply releases the starting arm and allows it to fly back and break the circuit, it is inoperative while the arm is being moved from the start- ing to the running position. h. Test. — Must, after 100 operations under the most severe normal conditions for which the device is designed, show no serious burning of the contacts or other faults, and 286 MODERN ELECTRICAL CONSTRUCTION. the release mechanism of motor-starting rheostats must not be impaired by such a test. Field rheostats, or main-line regulators intended for con- tinuous use, must not be burned out or depreciated by carry- ing the full normal current on any step for an indefinite period. Regulators intended for intermittent use (such as on electric cranes, elevators, etc.) must be able to carry their rated cur- rent on any step for as long a time as the character of the apparatus which they control will permit them to be used continuously. 61. Reactive Coils and Condensers. a. Reactive coils must be made of non-combustible ma- terial, mounted on non-combustible bases and treated, in general, as sources of heat. b. Condensers must be treated Hke other apparatus oper- ating with equivalent voltage and currents. They must have non-combustible cases and supports, and must be isolated from all combustible materials and, in general, treated as sources of heat. 62. Transformers. (For installation rules, see Nos. it, is, 13 A and 36.) a. Must not be placed in any but metallic or other non- combustible cases. On account of the possible dangers from burn-outs in the coils. (See note under No. 11 a.) It is advised that every transformer be so designed and connected that the middle point of the secondary coil can be reached if, at any future time, it should be desired to ground it. b. Must be constructed to comply with the following tests : 1. Shall be run for eight consecutive hours at full load in watts under conditions of service, and at the end of that time the rise in temperature, as meas- ured by the increase of resistance of the primary coil, shall not exceed 175 degrees Fahrenheit (97 degrees Centigrade). I ry 2 1 FITTINGS, MATERIALS, ETC. 287 2. The insulation of transformers when heated shall withs.tand continuously for five minutes a differ- ence of potential of 10,000 volts (alternating) be- tween the primary and secondary coils and be- tween the primary coils and core, and a no-load "run" at double voltage for thirty minutes. 63. Lightning Arresters. (For installation rules, see No. 5.) a. Lightning arresters mus.t be of approved construc- tion. (See list of Electrical Fittings.) Class E. < MISCELLANEOUS. 64. Signaling Systems. Governing wiring for telephone, telegraph, district mes- senger and call-hell circuits, lire and burglar alarms, and all similar systems which are hazardous only because of their liability to become crossed with electric light, heat or pozver circuits. a. Outside wires should be run in underground ducts or strung on poles, and, kept ofif of the roofs of buildings, ex- cept by special permission of the Inspection Department hav- ing jurisdiction, and must not be placed on the same cross- arm with electric light or power wires. They should not oc- cupy the same duct, manhole or handhole of conduit systems with electric light or power wires. Sing-le manholes, or handholes, may be separated in sec- tions by means of partitions of brick or tile so as to be con- sidered as conforming- with the above rule. The liability of accidental crossing- of overhead sig-naling circuits with electric lig-ht and power circuits may be g-uarded against to a considerable extent by endeavoring- to keep the two classes of circuits on different sides of the same street. Wlien the entire circuit from Central Station to building* is run in underground conduits, Sections b to m inclusive do not apply. h. When outside wires are run on same pole with electric light or power wires, the dis.tance between the two inside pins of each cross-arm must not be less than twenty-six inches. Sig-naling- wires being- smaller and more liable to break and fall, should g-enerally be placed on the lower cross-arms. c. Where the wires are attached to the outside walls of buildings they must have an approved rubber insulating cov- ering (see No. 41), and on frame buildings or frame portions of other buildings shall be supported on glass or porcelain in- sulators, or knobs. d. The wires from last outside support to the cut-outs or MISCELLANEOUS. 289 protectors must be of copper, and must have an approved rubber insulation (see No. 41) ; must be provided with drip loops immediately outside the buildings and at entrance ; mus.t be kept not less than two and one-half inches apart, ex- cept when brought in through approved metal-covered cables. e. Wires must enter building through approved non-com- bustible, non-absorptive insulating bushings sloping upward from the outside. Installations where the Current Carrying Parts of the Ap- paratus Installed are Capable of Carrying Indefinitely a Current of Ten Amperes. f. An all-metallic circuit shall be provided, except in telegraph systems. g. At the entrance of wires to buildings, approved single pole cut-outs, designed for 251-600 volts potential and con- taining fuses rated at not over ten amperes capacity, shall be provided for each wire. These cut-outs must not be placed in the immediate vicinity of easily ignitible stuff, or where exposed to inflammable gases, or dust or to flyings of com- bustible material. h. The wires inside building shall be of copper not less than No. 16 B. & S. gage, and must have insulation and be supported, the same as would be required for an in- stallation of electric light or power wiring, 0-600 volts poten- tial. i. The instruments shall be mounted on bases con- structed of non-combustible, non-absorptive insulating ma- terial. Holes for the supporting screws must be so located, or countersunk, that there will be at least one-half inch space, measured over the surface, between the head of the screw and the nearest live metal part. Installations where the Current Carrying Parts of the Ap- paratus Installed are Not Capable of Carrying Indefi- nitely a Current of Ten Amperes, j. Must be provided with an approved protective device located as near as possible to the entrance of wires to build- ing. The protector must not be placed in the immediate 290 MODEKN ELECTRICAL COXSTErCTION. vicinit}' of easily ignitible stuff, or where exposed to inflam- mable gases, or dust or flyings of combustible material. k. Wires from entrance to building to protector must be supported on porcelain insulators, so that they will come in contact with nothing except their designed supports. /. The ground wire of the protective device shall be run in accordance with the following requirements : 1. Shall be of copper and not smaller than No. 18 B. & S. gage. 2. Must have an approved insulating covering as de- scribed in No. 41, for voltages from .to 600. except that the preservative compound specified in No. 41, Section h, may be omitted. 3. Must run in as straight a line as possible to a good permanent ground. This may be obtained by connecting to a water or gas pipe connected ,to the street mains or to a ground rod or pipe driven in permanently damp earth. When con- nections are made to pipes, preference shall be given to water pipes. If attachment is made to gas pipe, the connection in all cases must be made between the meter and the street mains. In every case the connection shall be made as near as possible to the earth. When the ground wire is attached to water or gas pipes, these pipes shall be thoroughly cleaned and tinned with resin flux solder, if such a method is practicable ; the ground wire shall then be wrapped tightly around the pipe and thoroughly soldered to it. When the above method is impracticable, then if there are fittings where a brass plug can be inserted, the ground wire shall be thoroughly soldered to it ; if there are no such fittings, then the pipe shall be thoroughly cleaned and an approved ground clamp fastened to an exposed portion of the pipe and the ground wire well soldered to the ground clamp. MISCELLANEOUS, 291 When the ground wire is attached to a ground rod driven into the earth, the ground wire shall be soldered to the rod in a similar manner. Steam or hot-water pipes must not be used for a pro- tector ground, m. The protector to be approved must comply with the following requirements : For Instrument Circuits of Telegraph Systems. 1. An approved single pole cut-out, in each wire, de- signed for 2,000 volts potential, and containing fuses rated at not over one ampere capacit}^ When main line cut-outs are installed as called for in section g, the instrument cut-outs may be placed between the switchboard and the instrument as near the switch- board as possible. For All Other Systems. 1. Must be mounted on non-combustible, non-absorptive insulating bases, so designed that when the protector is in place all parts which may be alive will be thoroughly insulated from the wall to which the pro- tector is attached. 2. Must have the following parts : A lightning arrester which will operate with a difference of potential between wires of not over 500 volts, and so arranged that the chance of accidental grounding is reduced to a minimum. A fuse designed to open the circuit in case the wires be- come crossed with light or power circuits. The fuse must be able to open the circuit without arcing or serious flashing when crossed with any ordinary com- mercial light or power circuit. A heat coil, if the sensitiveness of the instrument de- mands it, which will operate before a sneak current can damage the instrument the protector is guard- ing. Heat coils are necessary in all clrciiits normally closed through mag-net windings, which cannot indefinitely carry a current of at least five amperes. The heat coil is designed to warm up and melt out with a 292 MODEKN ELECTRICAL CONSTRUCTION. current large enough to endanger the instruments if con- tinued for a long time, but so small that it would not blow the fuses ordinarily found necessary for such in- struments. The small currents are often called "sneak" currents. 3. The fuses must be so placed as to protect the arrester and heat coils, and the protector terminals must be plainly marked "line," "ins.trument," "ground.'' An easily read abbreviation of the above words will be al- lowed. The Pollowing- Rules Apply to All Systems whether the Wires from the Central Office to the Building- are Overhead or Underg-round. n. Wires beyond the protector, or wires inside buildings where no protector is used, must be neatly arranged and se- curely fastened in place in some convenient, workmanlike manner. They must not come nearer than six inches to any electric light or power wire in the building unless encased in approved tubing so secured as .to prevent its slipping out of place. The wires would ordinarily be insulated, but the kind of insulation is not specified, as the protector is relied upon to stop all dangerous currents. Porcelain tubing or approved flexible tubing may be used for encasing wires where required as above. 0. Wires where bunched together in a vertical run within any building must have a fire-resisting covering sufficient to prevent the wires from carrying fire from floor to floor unless they are run either in non-combustible tubing or in a fireproof shaft, which shaft shall be provided with fire stops at each floor. Signaling wires and electric light or power wires may be run in the same shaft, provided that one of these classes of wires is run in non-combustible tubing, or provided that when run otherwise these two classes of wires shall be sep- arated from each other by at least two inches. In no case shall signaling wires be run in the same tube with electric light or power wires. Ordinary rubber Insulation is inflammable, and when a number of wires are contained in a shaft extending througn a building they afford! a ready means of carrying fire from floor to floor, unless they are covered with a flre-resisting I MISCELLANEOUS. 293 material, or unless the shaft is provided with fire stops at each floor. 65. Electric Gas Lighting. a. Electric gas lighting must not be used on the same fixture with the electric light. The above rule does not apply to frictional systems of gas lighting-. 65 A. Moving Picture Machines . a. Arc lamp used as a part of moving picture machines must be constructed similar to arc lamps of theaters and wiring of same must not be of less capacity than No. 6 B. & S. gage. (See No. 31A d. [1].) b. Rheostats must conform to rheostat requirements for theater arcs. (See No. 31 A d [1].) c. Top reel must be encased in a steel box with hole at the bottom only large enough for film to pass through and cover so arranged that this hole can be instantly closed. No solder to be used in the construction of this box. d. A steel box must be used for receiving the film after being shown, with a hole in the top only large enough for the film to pass through freely, with a cover so arranged that this hole can be instantly closed. An opening may be placed at the side of the box to take the film out, with a door hung at the top, so arranged that it cannot be entirely opened, and provided with spring catch to lock it closed. No solder to be used in the construction of this box. e. The handle or crank used in operating the machine must be secured to the spindle or shaft, so that there will be no liability of its coming off and allowing the film to stop in front of lamp. f. A shutter must be placed in front of the condenser, arranged so as to be readily closed. g. Extra films must be kept in metal box with tight fit- ting cover. h. Machines must be operated by hand (motor driven will not be permitted). i. Picture machine must be placed in an enclosure or house made of suitable fireproof material, be thoroughly 294 MODERN ELECTEICAL COXSTEUCTION. ventilated and large enough for operator to walk freely on : either side of or back of machine. All openings into this ' booth must be arranged so as to be entirely closed by doors j or shutters constructed of the same or equally good fire- { resisting material as the booth itself. Doors or covers must j be arranged so as to be held normally closed by spring ] hinges or equivalent devices. 66. Insulation Resistance. The wiring in any building must test free from grounds ; /. e., the complete installation must have an insulation be- tween conductors and between all conductors and the ground (not including attachments, sockets, recep.tacles, etc.), not less than that given in the following table : Up to 5 amperes 4,000,000 ohms. 10 2,000,000 25 800,000 50 400.000 100 200,000 200 100,000 400 50,000 800 25,000 ,600 12,500 The test must be made with all cut-outs and .safety de- vices in place. If the lamp sockets, receptacles, electroliers, etc., are also connected, only one-half of the resistance speci- fied in the table will be required. CLASS F. MARINE WORK. 68. Generators. a. Must be located in a dry place. b. j\Inst have their frames insulated from their bed- plates. c. Must each be provided with a waterproof cover. d. Must each be provided with a name-plate, giving the maker's name, the capacity in volts and amperes, and the normal speed in revolutions per minute. 69. Wires. a. Must be supported in approved moulding or conduit, except at switchboards and for portables. Special permission may be given for deviation from this rule in dynamo-rooms. b. Mus.t have no single wire larger than No. 12 B. & S. gage. Wires to be stranded when greater carrying capacity is required. No single solid wire smaller than No. 14 B. & S. gage, except in fixture wiring, to be used. Stranded wires must be soldered before being fastened under clamps or binding- screws, and when they have a con- ductivity greater than that of No. 8 B. «& S. gage copper wire they must be soldered into lugs. c. Splices or taps in conductors must be avoided as far as possible. Where it is necessary to make them they must be so spliced or joined as to be both mechanically and elec- trically secure without solder. They mus.t then be soldered, to insure preservation, covered with an insulating compound equal to the insulation of the wire, and further protected by a waterproof tape. The joist must then be coated or painted with a w"aterproof compound. All joints must be soldered unless made with some form of approved splicing device. 296 MODERN ELECTRICAL CONSTRUCTION. For Moulding Work. d. Must have an approved insulating covering. The insulation for conductors, to be approved, must be at least 3-32 of an inch in thickness and be covered with substantial waterproof braid. The physical characteristics shall not be affected by any chang-e in temperature up to 200 degrees Fahrenheit (93 de- grees Centigrade). After two weeks' submersion in salt water at 70 degrees Fahrenheit (21 degrees Centigrade), it must show an insulation resistance of 100 megohms per mile after three minutes' electrification with 550 volts. e. Must have, when passing through water-tight bulk- heads and through all decks, a metallic stuffitig tube lined v«^ith hard rubber. In case of deck tubes, they must be boxed near deck to prevent mechanical injury. /. Must be bushed with hard rubber tubing, one-eighth of an inch in thickness, when passing through beams and non-water-tight bulkheads. For Conduit Work. g. Must have an approved insulating covering. The insulation for conductors, for use in lined conduits, to be approved, must be at least 3-32 of an inch in thickness and be covered with a substantial waterproof braid. The physical characteristics shall not be affected by any change in temperature up to 200 degrees Fahrenheit (93 degrees Centigrade). After two weeks' submersion in salt water at 70 degrees Fahrenheit (21 degrees Centigrade), it must show an insu- lation resistance of 100 megohms per mile after three minutes' electrification with 550 volts. For unlined metal conduits, conductors must conform to the specifications given for lined conduits, and in addition have a second outer fibrous covering at least one thirty-sec- ond of an inch in thickness and sufficiently tenacious to withstand the abrasions of being hauled through the metal conduit. MARINE WORK. -;:»' h. Must no.t be drawn in until the mechanical work on the conduit is completed and same is in place. i. Where run through coal bunkers, boiler rooms, and where they are exposed to severe mechanical injury, must be encased in approved conduit. 70. Portable Conductors. a. Must be made of two stranded conductors each hav- ing a carrying capacity equivalent to not less than No. 14 B. & S. gage, and each covered with an approved insulation and covering. Where not exposed to moisture or severe mechanical in- jury, each stranded conductor must have a solid insulation at least one thirty-second of an inch in thickness, and must show an insulation resistance between conductors, and be- tween either conductor and the ground, of at least fifty meg-ohms per mile after two weeks' submersion in water at 70 degrees Fahrenheit (21 degrees Centigrade), and be pro- tected by a slow-burning, tough-braided outer covering. Where exposed to moisture and mechanical injury (as for use on decks, holds and fire-rooms) each stranded conductor shall have a solid insulation, to be approved, of at least one- thirty-second of an inch in thickness and protected by a tough braid. The two conductors shall then be stranded together, using a jute filling. The whole shall then be covered with a layer of flax, either woven or braided, at least one thirty- second of an inch in thickness and treated with a non- inflammable waterproof compound. After one week's sub- mersion in water at 70 degrees Fahrenheit (21 degrees Centi- grade), it must show an insulation between the two con- ductors, or between either conductor and the ground, of fifty megohms per mile. 71. Bell or Other wires. a. Must never be run in same duct with lighting or power MODERN ELECTRICAL CONSTRUCTION. 72. Table of Capacity of Wires. Actual No. of Strands Area Size of B. & S. G. CM. Strands. B. & S. G. Amperes 19 1,288 18 1,624 '3 17 2,048 16 2,583 • • 1 *6 15 3,257 14 4,107 12 12 6,530 17 9,016 "7 i9 21 11,368 7 18 25 14,336 7 17 30 18,081 7 16 35 22,799 7 15 40 80,856 19 18 50 38,912 19 17 60 49,077 19 16 70 60,088 37 18 85 75,776 37 17 100 99,064 61 18 120 124,928 61 17 145 157,563 61 16 170 198,677 61 15 200 250,527 61 14 235 296,387 91 15 270 373,737 91 14 320 413.639 127 15 340 "When greater conducting area than that of 12 B. & S. gage is required, tlie conductor shall be stranded in a series of 7, 19, 37, 61, 91 or 127 wires, as may be required; the strand consisting- of one central wire, the remainder laid around it concentrically, each layer to be twisted in the op- posite direction from the preceding-. 73. Switchboard. a. Must be made of non-combustible, non-absorptive insulating material, such as marble or slate. h. Must be kept free from moisture, and must be located so as to be accessible from all sides. c. Must have a main switch, main cu,t-out and ammeter for each generator. Must also have a voltmeter and ground detector. d. Must have a cut-out and switch for each side of each current leading from board. MARINE WORK. 299 e. Must be wired with conductors having an insulation as required for moulding or conduit work and covered with a substantial flame-proof braid. 74. Resistance Boxes. {For construdtion rules, see No. 60.) a. Must be located on switchboard or away from com- bustible material. When not placed on switchboard they must be mounted on non-inflammable, non-absorptive insulat- ing material. 75. Switches. {For construciion rules, see No. ^i.) a. When exposed ,to dampness, they must be enclosed in a water-tight case. b. Must be of the knife pattern when located on switch- board. c. Must be provided so .that each freight compartment may be separately controlled. 76. Cut-Outs. {For construction rules, see N'o. 5^.) a. Must be placed at every point where a change is made in the size of the wire (unless the cut-out in the larger wire will protect the smaller). b. In such places as upper-decks, holds, cargo spaces and fire-rooms, a water-tight and fireproof cut-out may be used, connected directly to mains when such cut-out supplies cir- cuits requiring not more than 660 watts energy. c. When placed anywhere except on switchboards and certain places, as cargo spaces, holds, fire-rooms, etc., where it is impossible to run from center of distribution, they must be in a cabinet lined with fire-resisting material. d. Except for motors, searchlights and diving lamps must be so placed that no group of lamps, requiring a current of more .than 660 watts, shall ultimately be dependent upon one cut-out. MODERN ELECTRICAL CONSTRUCTION. 77. Fixtures. a. Must be mounted on blocks made from well-seasoned lumber treated with two coats of white lead or shellac. b. Where exposed to dampness, the lamp must be sur- rounded by a vapor-proof globe. c. Where exposed to mechanical injury, the lamp must be surrounded by a globe protected by a stout wire guard. d. Must be wired with same grade of insulation as port- able conductors which are not exposed to moisture or mechan- ical injury. e. Ceiling fixtures over two feet in length must be pro- vided with stay chains. 78. Sockets. (For construction rules, see No. 33.) 79. Wooden Mouldings. (For construction rules, see No. ^o.) a. Where moulding is run over rivets, beams, etc., a back- ing strip must first be put up and the moulding secured to this. b. Capping must be secured by brass screws. 80. Interior Conduits. (For installation rules, see No. 25.) (For construction rules, see No. 49.) 81. Signal Lights. a. Must be provided with approved telltale board, located preferably in pilot house, which will immediately indicate burned out lamp. 82. Motors. a. Must be wired under the same precautions as with current of same volume and potential for lighting. The motor and resistance box must be protected by a double-pole cut- out and controlled by a double-pole switch, except in cases where one-quar.ter horse power or less is used. I MARINE WORK. 301 The motor leads or branch circuits must be designed to carry a current at least 25 per cent greater than that for which the motor is rated, in order to provide for the inevitable occasional overloading of the motor, and the increased cur- rent required in starting, without overfusing the wires, but where the wires vmder this' rule would be overfused, in order to provide for the starting current, as in the case of many of the alternating current motors, the wires must be of such size as to be properly protected by these larger fuses. In general, motors should preferably have no exposed live parts. b. Must be thoroughly insulated. Where possible, should be set on base frames made from filled, hard, dry wood and raised above surrounding deck. On hoists and winches they must be insulated from bed-plates by hard rubber, fiber or similar insulating material. c. Must be covered with a waterproof cover when not in use. d. Mus.t each be provided with a name-plate giving maker's name, the capacity in volts and amperes, and the normal speed in revolutions per minute. 83. Insulation Resistance. The wiring in any vessel must test free from grounds; i. e., the complete installation must have an insulation be- tween conductors and between all conductors and the ground (not including attachments, sockets, receptacles, etc.) of not less than the following: Up to 25 amperes 50 " 800,000 ohms 400,000 " 100 " 200 000 " 200 " 100,000 " 400 " 50,000 " 800 " 25,000 " 1.600 " 12.500 " All cut-outs and safety devices in place in the above. Where lamp sockets, recep.tacles and electroliers, etc., connected, one-half of the above will be required. PRACTICAL HINTS. 303 PRACTICAL HINTS. A full description of the Wheatstone bridge, the telephone, magneto and other instruments, as well as the many ways of their application in testing for defects and for circuits in elec- trical installations having been given in a previous work of the authors (IViring Diagrams and Descriptions) it is not thought necessary to repeat them here, especially as a work of this kind is necessarily limited in diagrams which would be re- quired to a full understanding of methods. This chapter will, therefore, consist only of such hints and instructions as apply to general work. An electric light circuit may be tested for "short circuit" by connecting an incandescent lamp in place of one of the fuses. If the lamp burns while there are no lamps in circuit, there is sure to be a short circuit. A low candle-power lamp will indi- cate with less current than a high-candle-power lamp and is, therefore, better. If no lamp is available a small fuse should first be tried. A test for "ground" may be made in the same way, but the lamp must be connected to both sides in turn and the fuse left Figure 168 out. If the main system to which the circuit to be tested con- nects is not grounded, a temiporary ground must be put on. This is best done by connecting a lamp with one wire to a gas or water pipe and the other to the "live" binding screw on the opposite side of cutout to that in v/hich the other lamp is con- nected. Thus, in Figure 168, if a ground should exist at 3 and the lamp be connected to gas pipe, as shown, the test lamp at 1 would burn. MODERN ELECTRICAL CONSTRUCTION. If a voltmeter were connected in place of either of the lamps, the test would be much more searching. With 3-wire systems no ground need be put on, as the neu- tral wire will always be found grounded. The lamp need be tried in the outside fuses only. This test will be more search- ing if lamps are placed in all sockets connected. In placing fuses in the 3-wire, 110-220 volt system, the neu- tral wire should always be fused first. By reference to Figure 169 it will be seen that while the neutral fuse in main blocks a is out, the two circuits of lamps c and d must burn in series; that is, just as much current must pass through one circuit as through the other. So long as there is an equal number of lamps in each circuit there is no trouble ; but should most of the lamps in one circuit be turned off, those remaining would have to carry all the current that passes through the lamps of the other circuit. This current would overheat them and break, or burn them out in a very short time. If the neutral fuse is in place, each circuit is inde- pendent of the other and the neutral wire only carries the difference in current between the two sets of lamps. In order to insure against a neutral fuse "blowing" first in case of trouble, it is generally made heavier than in the outside wires. When a 3-wire circuit is to be cut off, the outside fuses should • be drawn first. In order to find which is the "neutral" wire, two 110 volt lamps are connected in series and the wires from them brought in contact with two of the three wires. If both lamps burn at full candle power we have 220 volts, which is the pressure of the outside wires, and, therefore, the other wire must be the neu- tral. If the lamps burn only at half candle power, we have only 110 volts and one of the wires must be the neutral. That wire which gives 110 volts with either one of the other two wires is the neutral; this wire should always be run in the center between the other two. I PRACTICAL HINTS. S06 A test for the neutral wire can also be made by connecting a lamp to ground. A lamp connected this way will burn from either of the outside wires, but not from the neutral. If the neutral wire should be connected to any but the middle binding post of 3-wire cutouts and the wutside wire to the other two, one-half of the lamps would be almost imme- diately destroyed, being subject to 220 volts, while the other half would burn properly. If a short circuit occurs, say at e, Figure 169, on one side of a 3-wire system and blows the neutral fuse on that side of the circuit, we shall have 220 volts on the lamps on the oppo- site side. This will quickly burn them out. Most of these c <> « « §' [iio «d,*'>'><'<''><'<^*<'* 6 6 (J-g fifg] i>i>f>i>i>t>/)t?t>i?t>i, + ! a Figure 169 troubles are avoided to some extent by the use of such branch cutouts as shown. This confines trouble of this kind to the mains. On any system having a neutral wire or a wire on one side grounded, if a ground on either of the other wires occurs, the trouble can be temporarily remedied by simply changing the two wires of that circuit at the cutout. This will trans- fer the ground to the side already grounded, so that it will not interfere with operation. The ground must, however, be cleared up at once as no grounding is ever allowed inside of any building. When strip cutouts are set horizontally and there is no 306 MODERN ELECTRICAL CONSTRUCTION. bridge between opposite polarities, there will be the possibility of a partially melted upper fuse sagging down and forming a short circuit. On panel boards where fuses are set too close together, the heat of one fuse while blowing will often blow the next fuse above it. If large fuses are enclosed in small and very tight cabi- nets, the vapors formed by blowing will often cause short circuits. Before installing fuses in a "loaded"' circuit, it is advisable to disconnect as many lights and other devices as possible. If there is a main switch this can easily be done. If there is no such switch on that part of the system, the task of placing fuses is somewhat hazardous ; for at the very instant that the second fuse touches its terminal a great rush of current will flow. If there happens to be a "short" on the line both fuses will probably blow and may burn the operator's hands anca face severely. In order to avoid this, extremely careful manip- ulation is necessary. The first fuse can be placed without any difficulty, as there will be no current flow unless the cir- cuits are grounded. Before attempting to place the second fuse the circuits may be tested for "shorts" by placing a "jumper" (a piece of wire heavy enough so that it will not be heated by the current it is to carry) with the ends on the other fuse terminals. This "jumper" will complete the cir- cuit and, if all is in order the lights will burn. If there are two men, one may hold the jumper while the other places the fuse, but it should be placed as quickly as possible, especially if the circuit has a motor load, for these will be started very soon after the lights come on and will greatly increase the current. If there is but one man the jumper may be tem- porarily fastened to the mains. A jumper is not absolutely necessary even with large fuses, for if the last contact is made quickly and held steady, there PRACTICAL HINTS. 307 will be very little arcing; one should, however, provide all pro- tection possible. If a piece of asbestos is at hand, it may be used to cover the fuses, so as to protect the hands and face from melted metal. Before attempting to re-fuse a circuit, note condition of cutout block. If there is evidence of a great flash, it is very likely that the fuse was blown by a short circuit. If the blowing was caused by a slight overload or loose contact, the destructive effect will be much less. Much trouble can be prevented by cleaning terminals of fuse blocks occasionally and going over nuts and screws to see that they are tight. In Figure 170, a shows the proper way of connecting small wires into such terminals. This method prevents the screw from cutting into the main wire and allowing it to break. A wire should always be bent around the binding post of switch or cutout in the direction in which the nut which is to Figure 170 hold it must turn to be fastened as in c. If a wire is not long enough to be bent around the post or screw, a small piece of wire should be placed opposite it so as to give a level bearing to nut or washer. See h. Plug cutouts having their metal parts projecting above the porcelain, as shown at d, should be connected, whenever pos- sible, so that these metal parts are dead when fuses are with- drawn. This will prevent many accidental short circuits. The positive and negative wires of a circuit can easily be determined by immersing both wires in a little water, keeping 308 :,xODERN ELECTRICAL CONSTRUCTION. them an inch or so apart. Small bubbles will soon appear at the negative wire. If an arc lamp has been properly connected, the upper car- bon will be heated much more than the lower and will remain red longer. An arc lamp improperly connected is said to be burning "upside down" and will at once manifest itself by the strong light thrown against the ceiling. It is very often found necessary to determine the capacity of a cable which is already installed and where it is impossible to get at the separate wires of which it is formed. As cables are usually made up in a uniform manner, as shown in the table below, their capacity can be determined by the following method : To find the number of circular mils in a cable made up of wires of uniform size. Measure diameter of cable, count number of wires in outside layer, and, referring to the table below, find the same number in the first column; divide the diameter of cable by the number set opposite this in the second column. This will give the diameter of each wire. Multiply this diameter by itself and then by the number of wires contained in cable as given in the third column. All measurements should be expressed in mils (1/1,000 inch) and the result will be the circular mils contained in cable. \ Outside layer 6 12 18 24 30 36 42 wires 3 5 7 9 11 13 15 times diameter 19 37 61 91 127 169 wires in cable The various figures in Figure 171 are designed to show how many single wires may be run in one conduit. Under each figure is given a number which, if multipled by the diameter of the wire to be used will give the smallest diameter of tube which can contain the corresponding number of wires. Thus, for instance, if 12 wires are run through PRACTICAL HINTS. 310 MODERN ELECTRICAL CONSTRUCTION. one tube or conduit, the diameter of that conduit must be at least 4 1/3 times as great as the diame- ter of the wire to be used. Each figure illustrates the amount of spare room the corresponding number of wires leave, and it is necessary to use considerable judgment. Long runs will require more space, especially if the wires be quite large. Much also depends upon the nature of the insulation and the temperature. The figures are believed to be correct for single wires and can be followed for twin wires, as the same number of conductors arranged that way will not occupy as much space as single wires. The actual diameter of lined and unlined conduits are given in another table and may be referred to. The best way to accurately determine the diam- eter of small wire consists in cutting a number of short pieces and laying them together, then measuring over all and divid- ing the measurement by the number of wires. TRICKS OF THE TRADE. Cases have been known where it was requested to replace single pole switches by double pole, that the single pole switch was replaced as requested, but, instead of running both wires through it as required, only one wire had been properly brought into it and the other two binding posts filled out with short pieces of wire calculated to deceive the inspector. A test to detect this without disconnecting the switch is easily made. By reference to Figure 172 it will be seen that if a double pole snap switch is properly connected, current can be felt if the points a and b are touched with moistened fin- gers. If the switch is connected single pole, current can be felt at b and c, when the switch is open, only. On one occasion a wireman had run some wires on insu- lators along a ceiling and instead of soldering joints had care- TRICKS OF THE TRADE. 311 fully, in many places above the joints, smoked the ceiling with a candle in order to deceive an inspector. In several cases where an "over-all" test of insulation re- sistance was made, meter loops which had been run in con- tinuous pieces were found with the wire "nicked" with a knife and then broken, leaving the insulation nearly intact, but the circuit open. A similar trick is often worked with the ground wire of ground detectors. In other cases plugs with fuses removed were put in "bad" circuits. In one case the real circuit wires (concealed Figure 172 Figure 173 work) were disconnected from cutouts and pushpd back into the wall and short pieces connected instead. In another case where wire not up to requirements had been used and condemned, this wire, being run between joists and concealed by plastering, was pushed back and short pieces of approved wire stuck in at outlets. Sometimes in fished work after inspection the long pieces of loom reaching from outlet to outlet are withdrawn and short pieces at the outlets substituted. Lamp butts with wire terminals twisted together, or a strand of wire from lamp cord twisted around the base as shown in Figure 173 and screwed into the cutout are often used in place of fuses. The strand of cord is sometimes uSed to help out a fuse plug on an overloaded circuit. 312 MODERN ELECTRICAL CONSTRUCTION. Table of Carrying Capacity of Wires. The following table, showing the allowable carrying ca- pacity of copper wires and cables of ninety-eight per cent con- ductivity, according to the standard adopted by the American Institute of Electrical Engineers, must be followed in placing interior conductors. For insulated aluminum wire the safe carrying capacity is eighty-four per cent of that given in the following tables for copper wire with the same kind of insulation TABLE NO. I. Table A. Table B. Rubber Other Insulation. Insulation s. See No. 41. SeeNos. 42 to 44. B. & S. G. Amperes. Amperes. Circular Mils. 18 3 5... 1,624 16 6 . . . . 8... 2,583 14 12 16. .. 4,107 12 17 23. . . 6,530 10 24 32. . . 10,380 8 33 4G. . . 16,510 6 . .. . 46 65. .. 26,250 5 54 77... 33,100 4 65 . . . . 92. . . 41,740 3 76 110. . . 52,630 90 131. . . 66,370 1 107 156. . . 83,690 127 185... 105,500 00 150 220... 133,100 000 177 262... 167,800 0000 210 312. . . 211,600 ::;ircular Mils. 200,000 200 300 300,000 270 400 400,000 330 500 500,000 390 590 600,000 450 680 700,000 500 760 800,000 550 840 900,000 600 920 1,000,000 650 1,000 1,100,000 690 1,080 1,200,000 730 1,150 1,300,000. . . . 770 1,220 1,400,000 810 1.290 1,500,000 850 1,360 1,600,000 890 1,430 1,700,000 930 1,490 1,800,000 970 1,550 1,900,000 1,010 1,610 2,000,000 1,050 1,670 TABLES. 313 The lower limit is specified for rubber-covered wires to prevent gradual deterioration of the high insulations by the heat of the wires, but not from fear of igniting tlie insulation. The question of drop is not taken into consideration in the above tables. The carrying capacity of Nos. 16 and 18, B. & S. gage wire is given, but no smaller than No. 14 is to be used, except as allowed under Nos. 24 v and 45 b. WIRING TABLES. The wiring tables, II-VI, are arranged in the following manner : For each size of wire and voltage considered there is given (under the proper voltage and opposite the number of the wire under the heading B. & S.) the distance it will carry 1 ampere at a less designated at top of page. The same wire will carry 2 amperes only half as far at the same percentage of loss and again will carry I ampere twice as far at double the percentage of loss. From these facts we deduce the rule of these tables, which is : Multiply the distance in feet (one leg only) by the num- ber of amperes to be carried. Take the number so obtained and under the proper voltage find the number nearest equal to it. Opposite this number, under the heading B. & S., will be found the size of wire required. To illustrate : We have 22 amperes to carry a distance of 135 feet and the loss to be al- lowed is 3 per cent at 110 volts. We therefore multiply 135 X 22 = 2970, and turning to table IV., which is figured for 3 per cent loss, follow downward in the column under 110 until we reach the number nearest equal to 2970, which, in this case, is .3180 corresponding to a No. 7 wire. With this wire our loss will be slightly less than 3 per cent, while with No. 8 it would be somewhat in excess of 3 per cent. For three-wire systems using 110 volts on each side the column marked 220 volts should be used. The column marked 440 volts is provided for three-wire systems using 220 volts Llff 314 MODERN ELECTRICAL CONSTRUCTION. on each side. The sizes determined will be correct for all three wires in both cases,. The columns at the right, marked motors, are arranged in the same way, the only difference being, for greater con- venience, they are figured in horse-power feet instead of am- pere feet. For this reason we multiply the distance in feet by the number of horse-power to be transmitted and divide by the percentage of loss, all other operations remaining the same as under lights. When any considerable current is to be carried only a short distance the wire indicated by the de- sired loss will very likely not have sufficient carrying capacity; it is, therefore, always necessary to consult the table of carry- ing capacities. RULE FOR WIRING TABLES. For lights, find the ampere feet (one leg) and under the proper voltage find the number equal to this or the next larger; opposite this number, in the column marked B. & S., will be found the size of wire required. For motors, proceed in the same way, using horse- , power feet instead of ampere feet. For alternating currents, the results obtained by multi- plying the amperes (or horse-power) by the feet, should be multiplied by the following factors: 1.1 for single-phase systems, all lights. 1.5 for single-phase systems, all motors. For two-phase, four-wire, or three-phase, three-wire systems, each wire need be only one-half as large as for single-phase systems and the number obtained may, there- fore, be divided by two. 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It is often necessary to reinforce mains which have becomJ overloaded. It is quite usual though often very incorrect, tq choose by the table of carrying capacities a wire of such sizi that the rated capacity of it and the wire to be re-enforced shall be equal to the load. Small wires have proportionately a much greater radiating surface than larger ones and there- fore their carrying capacity is proportionally greater. In order that a wire connected in parallel with another wire shall carry C. M. X a a certain current, its circular mils, must be equal A where C. M. stands for the cross-section of the larger wire in circular mils and A for the current to be carried by it, while a is the current to be carried by the extra wire. Table No. VII is calculated from this rule and shows the size of wire necessary to re-enforce another overloaded to a certain per cent as indicated in the top row. For instance, a 0000 wire overloaded 40 per cent requires re-enforcement by a No. 1 ; a No. 3 wire overloaded 20 per cent requires a No. 10 wire. Where large wires are re-enforced in this way by smaller ones great care must be taken that the larger wire cannot be acci- dentally broken or disconnected, since in such a case the whole load would be forced over the smaller wire and would likely result in a fire. The two wires should be securely soldered together. TABLE NO. VII. Am- peres. B. &S. 10% 20 30 40 50 60 70 80 90 100 210 0000 6 4 2 1 00 000 000 0000 0000 177 000 8 5 3 2 1 00 000 000 000 150 00 9 6 4 3 2 1 00 00 127 10 7 5 4 3 2 1 1 107 1 10 8 6 5 4 3 2 2 1 1 90 2 11 9 7 6 5 4 3 3 2 2 76 3 12 10 8 7 6 5 4 4 3 3 65 4 14 11 9 8 7 6 5 5 4 4 321 •m9 einii 0} 8}0Ti 89S 'sra9^ -sis 8JTA-89jq'j nosipa JO sanpsds Joj— aioN XI a i« O- » « » ^ ts-S a- - - -. - a-^ '3 j^ :jt::S :s^^ :s:^;^ I S g r^;i;^i^ m a ^ •3c 2i« Si s ca^ 1 i fl- = = = - ' " ' ' :^^:^:^;5^ ^^^ :^ a g; ^i-i(M(MlMCr- ,-iTH(N(M S=s s 1-^ si O s 8(5 fl* " " " * ' ' ' * o m t» ■tJ s^ o !> g c8 ^ 1 cf o O- ; ; - « i : : : si '":^:^:s^ s*„„2 a g; rH^T-<(M(MfC S'S 1 w 1 U m ^ ^ O O C t- _ tH 0) Amperes ■35 Ampe ■100 ■300 *• 600 •• ■ lono " a 1 a " 2 ;^ 1 o c > 1 A ia ■ Sis aaS oog Ill ITiTSl AiODERN ELECTRICAL CONSTRUCTION. DIMENSIONS OF COPPER WIRE im S, V Weights l| ■^ . s, Areas circuk Mils. C.M.- 1000 feet Mile ag 6§ 0000 460. 211,600. 641. 3,382. .051 000 410. 168,100. 509. 2,687. .064 00 365. 133,225. 403. 2,129. .081 325. 105,625. 320. 1,688. .102 1 289. 83,521. 253. 1,335. .129 2 258. 66,564. 202. 1,064. .163 3 229. 52,441. 159. 838. .205 4 204. 41,616. 126. 665. .259 5 182. 33,124. 100. 529. .326 6 162. 26,244. 79. 419. .411 7 144. 20,736. 63. 331. .519 8 128. 16,384. 50. 262. .654 ,9 114. • 12,996. 39. 208. .824 10 102. 10,404. 32. 166. 1.040 11 91. 8,281. 25. 132. 1.311 12 81. 6,561. 20. 105. 1.6.53 13 72. 5,184. 15.7 83. 2.084 14 64. 4,096. 12.4 65. 2.628 15 57. 3,249. 9.8 52. 3.314 16 51. 2,601. 7.9 42. 4.179 17 45. 2,025. 6.1 32. 5.269 18 40. 1,600. 4.8 25.6 6.645 19 36. 1,296. 3.9 20.7 8.617 20 32. 1,024. 3.1 16.4 10.566 21 28.5 812.3 2.5 13. 13.283 22 25.3 640.1 1.9 10.2 16.85 23 22.6 510.8 1.5 8.2 21.10 24 20.1 404. 1.2 6.5 26.70 25 17.9 320.4 .97 5.1 33.67 26 15.9 252.8 .77 4. 42.68 27 14.2 201.6 .61 3.2 53.52 28 12.6 158.8 .48 2.5 . 67.84 29 11.3 127.7 .39 2. 84.49 30 10. 100. .3 1.6 107.3 31 8.9 79.2 .24 1.27 136.2 32 8. 64. .19 1.02 168.5 33 7.1 50.4 .15 .81 214.0 34 6.3 39.7 .12 .63 271.7 35 5.6 31.4 .095 .5 343.6 36 5. 25. .076 .4 431.6 Table giving the outside diameters of rubber covered wires for use on voltages less than 600. Size B. &S Gauge Solid Solid Strand- Strand- Wire Wire ed Wire ed Wire Solid Stranded Single Double Single Double Twin Wire Twin Wires Braid Braid Braid Braid 0000 47-64 54-64 52-64 59-64 54-64x101-64 •59-64x111-64 000 41-64 46-64 48-64 55-64 46-64X 87-64 55-64x103-64 00 38-64 43-64 43-64 48-64 43-64X 81-64 48-64X 91-64 36-64 40-64 40-64 45-64 40-64X 75-64 45-64X 85-64 1 33-64 37-64 37-64 42-64 37-64X 70-64 42-64X 79-64 2 29-64 33-64 32-64 37-64 33-64X 62-64 37-64X 69-64 3 27-64 31-64 30-64 34-64 31-64X 58-64 34-64X 64-64 4. 25-64 29-64 27-64 31-64 29-64X 54-64 31-64X 58-64 5 24-64 28-64 28-64X 52-64 6 22-64 26-64 24-64 28-64 26-64X 49-64 28-64X 52-64 8 18-64 22-64 20-64 23-64 22-64X 41-64 23-64X 42-64 10 16-64 20-64 18-64 21-64 20-64X 37-64 21-64X 38-64 12 15-64 19-64 16-64 20-64 19-64X 35-64 20-64X 36-64 14 14-64 18-64 15-64 19-64 18-64X 33-64 19-64X 34-64 16 10-64 13-64 13-64X 24-64 18 9-64 12-64 12-64X 22-64 Table giving the outside diameters of rubber covered Voltages between 600 and 3500. wires for use on Size B. &S. Gauge Solid Wire Single Braid Solid Wire Double Braid Strand- ed Wire Single Braid Strand- ed Wire Double Braid Solid Twin Wire Stranded Twin Wire 0000 000 00 1 2 3 4 5 6 8 10 12 14 49-64 46-64 41-64 38-64 35-64 33-64 31-64 29-64 28-64 27-64 24-64 22-64 21-64 20-64 56-64 53-64 46-64 43-64 40-64 38-64 36-64 33-64 32-64 31-64 28-64 26-64 25-64 24-64 53-64 50-64 47-64 42-64 39-64 36-64 34-64 31-64 28-64 26-64 24-64 22-64 21-64 61-64 57-64 53-64 46-64 43-64 40-64 38-64 35-64 32-64 30-64 28-64 26-64 25-64 56-64x105-64 53-64X 99-64 46-64X 87-64 43-64X 81-64 40-64X 75-64 38-64X 71-64 36-64X 67-64 33-64X 62-64 32-64X 60-64 31-64X 58-64 28-64X 52-64 26-64X 48-64 25-64X 46-64 24-64X 44-64 61-64x114-64 57-64x107-64 53-64X 99-64 46-64X 88-64 43-64X 82-64 40-64X 76-64 38-64X 72-64 35-64X 66-64 32-64X 60-64 30-64X 56-64 28-64X 52-64 26-64X 48-64 25-64X 46-64 NOTE. — These figures are taken from data furnished by one of the largest manufacturers of wire and are believed to be of at least as great dimensions as any standard wire on the market. Judgement must be used in applying these dimensions as the same size wire B. & S. gauge, of different makes often varies considerably in outside diameter. MODERN ELECTRICAL CONSTRUCTION. Outside Diameters of Rubber Covered Cables. Capacity in Diameter Cir. Mils. over Braid 1,500,000 113-64 1,250,000 107-64 1,000,000 97-64 950,000 95-64 900,000 94-64 850,000 93-64 800,000 89-64 750,000 87-64 700,000 83-64 650,000 81-64 600,000 79-64 550,000 76-64 500,000 73-64 450,000 68-64 400,000 66-64 350,000 64-64 300,000 61-64 250,000 59-64 Dimensions of Unlined Conduit. Nominal Actual Actual Thick- Internal Internal External ness of Diam. Diam. Diam. Walls Inches. Inches. Inches. Nearest 64th J 17-64 26-64 4-64 i 23-64 35-64 5-64 a 31-64 43-64 6-64 ^ 40-64 54-64 6-64 52-64 67-64 7-64 67-64 84-64 8-64 u 88-64 106-64 9-64 n 103-64 122-64 9-64 2 132-64 152-64 10-64 2h 157-64 184-64 13-64 3 196-64 224-64 13-64 Outside Diameters of Weather- proof Wire. Outside Diameters. Wire Solid Stranded 1,000,000 108-64 900,000 103-64 800,000 _i. 100-64 700,000 94-64 600,000 85-64 500,000 80-64 450,000 76-64 400,000 73-64 350,000 64-64 300,000 62-64 250,000 58-64 0000 50-64 55-64 000 47-64 51-64 00 39-64 43-64 36-64 39-64 1 32-64 35-64 2 30-64 33-64 3 27-64 30-64 4 25-64 28-64 5 22-64 24-64 6 20-64 22-64 8 17-64 18-64 10 16-64 12 14-64 14 12-64 16 10-64 18 8-64 Dimensions of Lined Conduit Nominal Actual Actual Internal Internal External Diameter Diameter Diameter Inches Inches Inches . 1 32-64 54-64 1 45-64 67-64 1 58-64 84-64 li 80-64 106-64 H 90-64 122-64 2 115-64 152-64 2i 144-64 184-64 3 176-64 224-64 TABLES. DIMENSIONS OF PORCELAIN KNOBS. Trade No. Height Diameters Hole Groove Height of \\ire 2i 3 1.^ 1 ■h 1 3 2i 1^ |- n 2 2 A 1 3 If A 1^ 3* 2 ^ T^ 4 W 14 1 4+ 1 U- Jg o li - A 2 5* li% 1 i A 1 7 1 i j^ 1 9 , 1- T^ A 3 10^ 1^ 1* g 1 Trade Height Width Size of Size of Number Hole Groove 1 U H 1 1* H u f 2 H tk 3 2i 2 I '.. A 7 2J 2 8 3f 2f 1" cable SIZES OF PORCELAIN TUBES. Size of Groove Size of Wire Size of Groove Size of Wire 7-32 5-16 13-32 9-16 14-12 B. & S. 10- 8 B. & S. 6-5-4 B. & S 3-2-1-0 B. & S. 3-4 7-8 1 1 1-4 0-0000 Stranded 250.000 C. M. 500 . 000 C. M. 750.000 C. M. MODERN ELECTlilCAL CONSTRUCTION. DIMENSIONS OF CLEATS. One-Wire Cleats. DuGGAN Cleat. No. 4 holds wires 16-8 B, & S. No. 7 No. 5 No. 6 No. 8 No. 2-00 000-300,000 C. M. 400,000-800,000 C. M. 900,000-1,200,000 C. M, Brunt Cleat. Stand. Number Width Length Groove 328 ? 2 i| holds wires 16-5 B. & i 329 1 21 i " " 8-3 331 -}| 2| H " •* 3-00 330 U 2-h i " " 4-1 332 1 i 2| H " " 0-0000 Two AND Three-Wire Cleats. Brunt. No. 334 2-wire holds wires . . , 16-8 B. & S No. 337 3 wire " " 16-8 B. & S DuGGAN. No. 3 2-wire holds wires 16-8 B. & 8. No. 2 2-wire " " 6-00 B. & S. No. 1 3 wire " " 16-8 B. & S. Pass & Seymour. No. A-3 2-wire holds wires 14-12 B. & S. No. 3 2-wire " " 14- 6 B. & S No. A-43 3-wire " " 14-12 B. & S No. 43 3-wire " " 14- 6 B. & S. TABLES. DIMENSIONS OF IRON SCREWS. APPROXIMATE. Diameter in Nearest B. & S. Greatest Length Fractions Gauge Obtainable I2S 15 1 1 lis 14 A 2 12 1 3 3% 11 u 4 9 1+ 5 8 24 6 N, 7 3 7 xis 7 3 8 --% 6 4 9 5 4 10 ®2 5 4 11 hi' 4 4 12 4 6 13 _?9. 3 6 14 1|- 3 6 15 1 2 6 16 bI 2 6 17 1 6 18 II 1 6 DIMENSIONS OF COMMON NAILS. APPROXIMATE Trade Diameter in Nearest B. & S. Length in No. Number Fractions Gauge Inches per lb. 2d its 13 1 875 3d B5 12 u 565 4d S 10 n 315 5d i 10 If 270 6d BI 9 2 ISO 7d s 9 2i 160 8d t¥8 8 2- 105 9d t¥s 8 22 95 lOd r\% 7 3 70 12d 6 3i 60 16d 5 6 34 50 20d /zg 4 4 30 Fine Nails .2d 3d 4d 15 13 1 li U 1350 770 470 MODERN ELECTRICAL CONSTRUCTION, RATING OF MOTORS. Full Load Currents. H. P. 110 VOLTS 220 VOLTS 500 VOLTS 1.9 .95 .42 2.7 1.35 .62 A 5. 2.50 1.15 7.5 3.75 1.70 9.2 4.60 2.10 2 17.5 8.75 4. 3 24.6 12.30 5.60 4 32. 16. 7.50 5 40. 20. 9.20 7i 57. 28.5 13. 10 76. 38. 17.5 15 110. 55. 25. 20 144. 72. 34. 25 176. 88. 40. 30 210. 105. 49. 35 250. 125. 57. 40 280. 140. 65. 45 320. 160. 75. 50 3.50. 175. 80. 60 430. 215. 100. 75 520. 260. 120. 100 700. 350. 160. 125 880. 440. 210. 150 1056. 530. 245. 175 1230. 615. 280. 200 1400. 700. 325. RATING OF INCANDESCENT LAMPS. 110 VOLTS 220 VOLTS C. P. Watts 18 Amperes C. P. Watts Amperes 4 .16 8 36 .16 6 24 .22 10 45 .20 8 30 .27 16 64 .29 10 35 .32 20 76 .35 12 40 .36 24 90 .41 16 56 .51 32 122 .55 20 70 .64 50 190 .86 24 84 .76 32 112 1.00 50 175 1.60 TABLES. 323' '.5 The Hewitt-Cooper Mercury Vapor lamp requires a current of about i amperes. The Nernst lamp consumes 88 watts per glower; for a 6 glower, 110 volt lamp, about 4.8 amperes. Series miniature lamps, operated 8 in series, on 110 volts, require a current of about .33 amperes for 1 candle power lamps, and 1 ampere for 3 candle power lamps. Tables showing the currents which will fuse wires of different sub- B. &S. Gauge Diam. Copper Aluminum Germar* Silver Iron 10 12 14 102. 81. 64. 333. 236. 165.7 246.5 174.4 122.8 170. 120.5 84.6 102.3 72.6 50.9 16 18 20 51. 40. 32. 117.7 81.9 58.5 87.1 60.7 43.4 60.1 41.8 29.9 36.1 25.2 18. 22 24 26 2.5.3 20. 16. 41.1 28.9 20.7 30.5 21.5 15.3 21.0 14.8 10.6 12.4 8.9 6.4 28 30 32 12.6 10. 8. 14.5 10.2 7.3 10.7 7.6, 5.4 7.4 5.2 3.7 4.5 3.1 2.3 34 36 6.3 5. 5.1 3.6 3.8 2.7 2.6 1.8 1.6 1.1 THE KING OF ALL— The Companion Volume to Modern Wiring Diagrams— Just from the Press EieoiHoat Wiring bum Gonsiruciion Taities B^ Henry C. Horstmann and Victor H. Tousley Contains hundreds of easy up-to-date tables covering everything on Electric Wiring. Bound in full Persian Morocco. Pocket size. Round corners, red edges. PRICE, NET, $1.50 Partial Table of Contents This Book contains atnong others: Tables for direct current calculations. Tables for alternating cur- rent calculations. These tables show at a glance the currents re- quired with any of the systems in general use, fcr any voltage, effici- ency, or power-factor, and by a very simple calculation (which can be mentally made), also the proper wire for any loss. Tables showing the small- est wire permissable with any system or num- ber of H. P. or lights under National Electri- cal Code" or Chicago rules. Very convenient for contractors. Tables for calculating the most economical loss. Tables and diagrams showing proper size of conduits to accommo- e all necessary combinations or nber of wires. T les and data for estimating at a glance the quantity of material re- quired in different lines of work. A 3 this is intended for a pocket-hand-book everything that would ■^^ makes it unnecessarily cumbersome is omitted. There is no padding. Every page is valuable and a time saver. This book will be used every day be the wireman, the contractor, engineer and architect. All parts are so simple that very little electrical knowl- edge is required to understand them. Sznt, all chrages paid to any address, upon receipt of price. mmu I mm l CO., Publishers, Cliicago DYNAMO TENDING yor ENGINEERS Or, ELECTRICITY FOR STEAM ENGINEERS By HENRY C. KOHSTMANN and VICTOR H. TOUSLEY, Authors of "Modern Wiring Diagrams and Descriptions for Electrical Workers." This excellent treatise is written by- engineers for engineers, and is a clear and comprehensive treatise on the prin- ciples, construction and operation of Dynamos, Motors, Lamps, Storage Bat- teries, Indicators and Measuring Instru- ments, as well as full explanations of the principles governing the generation of alternating currents and a descrip- tion of alternating current instruments and machinery. There are perhaps but few engineers who have not in the course of their labors come in contact with the electrical apparatus such as pertains to light and power distribution and generation. At the present rate of increase in the use of Electricity it is but a question of time when every steam installation will have in connecton with it an electrical generator, even in such buildings where light and power are supplied by some central station. It is essential that the man in charge of Engines, Boilers, Elevators, etc., be familiar with electrical matters, and it cannot well be other than an advantage to him and his employers. It is with a view to assisting engineers and others to obtain such knowledge as wil 1 enable them to intelligently manage such electrical apparatus as will ordinarily come under their control that this book has been vn^itten. The authors have had the co-operation of the best authorities, each in his chosen field, and the information given is just such as a steam engineer should know, To further this information, and to more carefully explain the text, nearly 100 illustrations are used, v^hieh, with perhaps a very few excep- tions, have been especially made for this book. There are many tables covering all sorts of electrical matters, so that immediate reference can be made without resorting to figuring. It covers the subject thoroughly, but so simply that any one can understand it fully. Any one making a pretense to electrical engineering needs this book. Nothing keeps a man down like the lack of training; nothing lifts him up as quickly or as surely as a thorough, practical knowledge of the work he has to do. This book was written for the man without an opportunity. No matter what he is, or what work he has to do, it ^ives him just such information and training as are required to attain success. It teaches just what the steam engineer should know in his engine room about electricity. 13mo, Cloth, 100 Illustrations. Sizo5i/^x7^. PRICE NET A I C|| Sold by bookselle rs general ly, or sent, all charges paid, upon vi>vU receipt of price ' FREDERICK J. DRAKE & CO., Publishers CHICAGO, ILL. Easy Electrical Experiment^ and How to Make Them By L. P. DICKINSON This is the very latest and m^sfl valuable work on Electricity for the amateur or practical Electrician pub- lished. It gives in a simple and easily understood language every thing you should know about Gal- vanometers, Batteries, Magnets, In-i duction, Coils, Motors, Voltmeters, Dynamos, Storage Batteries, Simple and Practical Telephones, Telegraph Instruments, Rheostat, Condensers, Electrophorous,' Resistance, Electro Plating, Electric Toy Making, etc. The book is an elementary hand book of lessons,^ experiments and inventions. It is a hand book for beginners, though it includes, as well, examples for the advanced students. The author stands second to none in the scientific world, and this exhaustive work will be found an invaluable assistant to either the Student or mechanic. Illustrated with hundreds of fine drawings; priiitef^ on a superior quality of paper. I2mo Cloth. Price, %U2S. _ Sent postpaid to any address upon receipt of prio IRCDERICK J. DRAKE & CO.. PubUshers. CHICAGO, ILL. A BOOK EVERY ENGINEER ^ND ELECTRICIAN SHOULD HAVE IN HIS POCKET. A COMPLETE ELECTRICAL REFERENCE LIBRARY IN ITSELF NEW EDITION H6e Handy Vest-Pocket ELECTRICAL DICTIONARY BY WM. L. WEBER, M.E. ILLUSTRATED CONTAINS upwards of 4,800 words, terms and phrases employed in the electrical profession, with ithelr definitions given in the most concise, lucid and comprehensive manner. The practical business advantage and the educational benefit derived from the ability to at once understand the meaning of some term involving the description, action or functions of a machine or apparatus, or the physi- cal nature and cause of certain phe- nomena, cannot be overestimated, and will not be, by the thoughtful assidu- ous and ambitious electrician, because he knows that a thorough understand- ing, on the spot, and in the presence of any phenomena, effected by the aid of his little vest-pocket book of refer- ence, is far more valuable and lasting in its imjjression upon the mind, than any memorandum which he might make at the time, with a view to the future consultation of some volumin- oiis standard textbook, and which is more frequently neglected or .forgotten than done. The book is of convenient size for carrying in the vest pocket, being only 2% inches by 5^ nches, and i4 inch thick; 324 pages, illustrated, and bound in two different styles : New £ditio!\. Cloth, Red Edges, Indexed . . 25c New Edition. Full Leather, Gold Edges, Indexed, 50c Sold by booksellers generally or sent postpaid to any address upon receipt of price. FREDERICK J. DRAKE & CO. PUBLISHERS CHICAGO, ILU JUST THE BOOK FOR BEGINNERS AND ELECTRICAL WORKERS WHOSE OPPORTUNITIES FOR GAINING INFORMATION ON THE BRANCHES OP ELECTRICITY HAVE BEEN LIMITED ELECTRICITY '^f, Made Simple By CLARK CARYL HASKINS A BOOK DEVOID OF TECHNICALITIES SIMPLE, PLAIN AND UNDERSTANDABLE There are many elementary books about electricity upon the market but this is the first one presenting the matter in such shape that the layman may under- stand it, and at the same time, not writ- ten in a childish manner. FOR ENGINEERS, DYNAMO MEN, FIREMEN, LINEMEN, WiREMEN AND LEARNERS. FOP STUl Y OR REFERENCE. This little work is not intended for the instruction oi experts, nor as a guide for professors. The author has endeavored throughout the book to bring the matter down to the level of those whose opportunities for gaining information on the branches treated have been limited. Four chapters are devoted to Static Electricity ; three each to Chemi- cal Batteries and Light and Power; two each to Terrestrial Magnetism and Electro-Magnetism; one each to Atmospheric Electricity; Lightning Rods; Electro -Chemistry; Applied Electro - Magnetism ; Force, Work and Energy; Practical Application of Ohm's Law; also a chapter upon Methods of Developing Electricity, other than Chemical. The large number of examples that are given to illi^rate the practi* cal application of elementary principles is gaining for it a reputation aa a text book for schools and colleges. In reviewing this book an eminent electrician says of it ; "All that 999 men out of 1000 want to know can be imparted in plain language and arithmetic. I therefore think that such a book as yours Is the kind that does the greatest good to the greatest number." I2mo, Cloth, 233 Pagfes, IO8 Illustrations Cff « f\g% For Sale by booksellers generally or sent postpaid to any address upon receipt of price, FREDERICK J. DRAKE & CO., Publishers CHICAGO. EJU THE MOST IMPORTANT BOOK ON ELECTRICAL CONSTRUCTION WORK FOR ELECTRICAL WORKERS EVER PUBLISHED. REVISED AND ENLARGED 1908 EDITION. MO DERN WIRING DIAGRAMS AND DESCRIPTIONS A Hand Book of practical diagrams and . information for Electrical Workers. By HENRY C. HORSTMANN and VICTOR H. TOUSLEY Expert Electricians. This grand little volume not only tells you how to do it, but it shows you. The hook contains no pictures of bells, batteries or other fittings ; you can see those anywhere. It contains no Fire Underwriters' rules ; you can get those free anywhere. It contains no elementary considera- tions; you are supposed to know what an ampere, a volt "or a "short circuit" is. And it contains no historical matter. All of these have been omitted to make room for "diagrams and de- scriptions" of just such a character as TForkers need. We claim to give all that ordinary electrical workers neecJ and nothing that they do not need. It shows you how to wire for call and alarm bells. For burglar and fire alarm. How to run bells from dynamo current, How to install and manage batteries. How to test batteries. How to test circuits. How to wire for annunciators; for telegraph and gas lighting. It tells how to locate "trouble" and "ring out" circuits. It tells about meters and transformers. It contains 30 diagrams of electric lighting circuits alone. It explains dynamos and motors ; altei-nating and direct current. It gives ten diagrams of ground detectors alone. It gives "Conapensator" and storage battery installation. It gives simple and explicit explanation of the " Wheatstone" Bridge and its uses as well as volt-meter and other testing. It gives a new and simple wiring table covering all voltages and all losses or distances. IGmo., 160 pages, 200 illustrations; full leather binding, tf^-l C[^\ round corners, red edges. Size 4x6, pocket edition. PRICE ^J) I .Ov^ Sold by booksellers generally or sent postpaid to any address upon receipt of price. FREDERICK J. DRAKE & CO., Publishers CHICAGO, ILL, SEP 38 I0U8