Engineering Library Copies of this report my be purchased at one dollar eaoh from the Secretary of . the American Institute of Electrical Engi- neers, 33 West 39th Street, New York, N.Y. REPORT OF THE AMERICAN COMMITTEE ON ELECTROLYSIS 1921 i?C ->* Engineering y.P-ary COMMITTEE American Institute of Electrical Engineers BION J. ARNOLD, Chairman, Chicago, Illinois. N. A. CARLE, Newark, New Jersey. F. N. Waterman, New York, N. Y. American Electric Railway Association L. P. CRECELIUS, Cleveland, Ohio. W. J. HARVIE, Syracuse, N. Y. G. W. VAN DERZEE, Milwaukee, Wisconsin. American Railway Engineering Association E. B. KATTE, New York, N. Y. MARTIN SCHREIBER, Newark, New Jersey. W. M. VANDERSLUIS, Chicago, Illinois. National Electric Light Association L. L. ELDEN, Boston, Mass. D. W. ROPER, Treasurer, Chicago, Illinois. PHILIP TORCHIO, New York, N. Y. American Gas Association WALTER C. BECKJORD, New York, N. Y. CHARLES F. MEYERHERM, New York, N. Y. H. C. SUTTON, Philadelphia, Pa. Natural Gas Association of America FORREST M. TOWL, New York, N. Y. THOMAS R. WEYMOUTH, Oil City, Pa. S. S. WYER, Columbus, Ohio. American Telephone and Telegraph Company A. P. BOERI, New York, N. Y. F. L. RHODES, New York, N. Y. H. S. WARREN, New York, N. Y. American Water Works Association ALFRED D. FLINN, New York, N. Y. NICHOLAS S. HILL, JR., New York, N. Y. E. E. MINOR, New Haven, Conn. National Bureau of Standards BURTON McCoLLUM, Washington, D. C. DR. E. B. ROSA,* Secretary, Washington, D. C. E. R. SHEPARD, - Washington, D. C. * Deceased. 6 PREFACE organizations they represent will aid materially in reducing the destructive effects due to electrolysis. The Committee, through its Research Subcommittee, has established a close working relationship with the National Bureau of Standards, which has been distinctly advantageous. The Committee regrets to chronicle the death in Washington on May 17, 1921, of its secretary, Dr. Edward B. Rosa, Chief Physicist of the National Bureau of Standards, one of its most efficient and esteemed members. October, 1921. BION J. ARNOLD, Chairman. TABLE OF CONTENTS CHAPTER 1. Principles and Definitions Page A. Electrolysis in General: 1. Electrolysis 15 2. Electrolyte, Electrode, Anode, and Cathode 15 3. Amount of Chemical Action 15 4. Cause of Current Flow 16 5. Electrolysis by Local Action 16 6. Anodic Corrosion 16 7. Secondary Reactions 16 8. Cathodic Corrosion 17 B. Electrolysis of Underground Structures. 9. General 17 10. Self Corrosion 17 11. Acceleration of Local or Self Corrosion 17 12. Stray Current 18 13. Anodic and Self Corrosion 18 14. Coefficient of Corrosion 18 15. Passivity 18 16. Polarization Voltage 18 17. Alternating or Frequently Reversed Direct Currents 19 18. Action on Underground Metallic Structures 19 19. Electrolysis Mitigation ". / 19 20. Electrolysis Survey 20 2 1 . Overall Potential Measurements ' 20 22. Potential Gradient 20 23. Potential Difference. ; 21 24. Arithmetical Average 21 25. Algebraic Average 21 26. Positive and Negative Areas 21 27. Drainage System 21 28. Uninsulated Track Feeder System 22 29. Insulated Negative Feeder System 22 CHAPTER 2. Design, Construction, Operation and Maintenance 1. Measures Tending both to Railway Economy and the Reduction of Stray Current 24 2. Measures Employed Solely for Electrolysis Prevention 24 (a) Applicable to Railways. (b) Applicable to Affected Structures. (c) Interconnection of Affected Structures and Railway Return Circuit. I. RAILWAYS A. Features Which Affect Electrolysis Conditions. 1. Track Construction and Bonding 25 (a) Importance of Rail Circuit 25 CONTENTS Page (b) Rail Bond Resistance and Tests 25 (c) Types of Bonds 26 Soldered Bonds 26 Brazed or Welded Bonds 26 Resistance Weld 26 Electric Arc Process 27 Oxy-Acetylene Process 27 Pin Expanded Terminal Bonds 27 Compressed Terminal Bonds 27 (d) Welded Rail Joints 28 Electric Rail Welding 28 Arc Welding 28 Cast Welding 28 Thermit Process 28 (e) Cross-Bonding 29 (f ) Special Track Work Bonding 29 (g) Bonding Tracks with Signal Systems 30 (h) Conductivity and Composition of Rails 30 2. Track Insulation 31 (a) Degrees of Insulation 31 Substantial Insulation 31 Partial Insulation 31 (b) Leakage to be Expected 32 3. Reinforcement of Rail Conductivity 32 4. Power Supply 33 (a) High Voltage d. c. Railways 34 (b) Source of Stray Currents 34 (c) Relation of Feeding Distance to Stray Currents and Overall Voltages 38 (d) Economic Considerations Involved in Additional Supply Stations 42 (e) Automatic Substations 44 (f) Location of Supply Stations 46 (g) Alternating Current Systems 46 5. Interconnection of Tracks. 47 B. Features of Railway Construction and Operation Employed for Electrolysis Mitigation. 1 . Insulated Negative Feeder System 49 (a) Description 49 (b) Application of Insulated Negative Feeders 53 Application to Interurban Lines 55 (c) Negative Boosters 57 2. Three-Wire System 57 (a) Description 57 (b) Insulation of Trolley Sections 59 (c) Costs 59 (d) Difficulties and Limitations 60 (e) Practicability 61 (f ) Extent of Adoption 62 CONTENTS 9 Page B. Features of Railway Construction (continued) 3. Reversed Polarity Trolley System 62 4. Periodic Reversal of Trolley Polarity .... 63 5. Double Contact Conductor Systems 65 II. UNDERGROUND STRUCTURES SUBJECT TO INJURY BY STRAY CURRENTS A. Location with Respect to Tracks. B. Cable Systems. 1. Avoidance of Accidental Contacts with Other Structures. . . 66 2. Conduit Construction 67 (a) Signal Cables 67 (b) Power Cables 68 3. Surface Insulation 69 4. Insulating Joints 70 C. Pipe Systems 1 . Surface Insulation 71 2. Insulating Joints 74 (a) New Work 74 (b) Cement Joints 76 (c) Leadite and Metallium 76 (d) Dresser Couplings 78 (e) Special Insulating Joints 78 (f ) Insulating Joints Applied to Existing Pipe Lines 78 3. Shielding 79 III. MEASURES INVOLVING INTERCONNECTION OF AFFECTED STRUCTURES AND RAILWAY RETURN CIRCUIT A. Electrical Drainage of Cable and Pipe Systems 81 1. Drainage of Cable Sheaths 83 (a) Method of Draining Cables 83 (b) Heating Effect of Stray Current on Cable Sheaths 84 2. Difference Between Cable Drainage and Pipe Drainage 88 3. Application of Drainage to Pipes 90 (a) Maintaining Pipes Negative to Earth 90 (b) Effect of Pipe Drainage on Current Interchange 90 (c) Effects of Different Kinds of Pipes and Joints 92 SUMMARY OF GOOD PRACTICE. A. Railways 92 1. Track Construction and Bonding 92 2. Track Insulation 93 3. Reinforcement of Rail Conductivity 93 4. Power Supply 94 5. Interconnection of Tracks : 94 6. Insulated Negative Feeder System 94 7. Three-wire System 95 8. Reversed Polarity Trolley System 95 9. Periodic Reversal of Trolley Polarity 96 10. Double Contact Conductor Systems 96 11. Alternating Current Systems 96 10 CONTENTS Page B. Affected Structures. 1. Location with Respect -to Tracks 96 2. Avoidance of Contact with Pipes and Other Structures 96 3. Conduit Construction 97 4. Insulating Joints in Cable Sheaths 97 5. Surface Insulation of Pipes and Cables 97 6. Insulating Joints in Pipes 97 7. Shielding 98 C. Interconnection of Affected Structures and Railway Return Circuit. 1. Cable Drainage 98 2. Pipe Drainage 99 CHAPTER 3. Electrolysis Surveys I. INTRODUCTION A. Purpose and Scope of Electrolysis Surveys. 1. Purpose of Electrolysis Surveys 100 2. Difficulty of Standardizing Survey Procedure 100 3. Information Obtainable by Electrolysis Surveys 100 B. Types of Surveys 101 C. General Preliminary Data. 1. Data on Underground Structures 102 2. Data on Railway Systems 102 D. Cooperation in Making Surveys 102 II. ELECTRICAL MEASUREMENTS A. Voltage Surveys 103 1. Measurement of Maximum Potential Drop Along Railways.. 104 (a) Importance of Maximum Potential Drop Measurements. 104 (b) Procedure in Making Maximum Drop Measurements. . 104 2. Potential Gradient Measurements 106 (a) Scope of Term 106 (b) Measurement of Potential Gradients in Tracks 106 3. Measurement of Potential Differences 107 (a) Purpose of Measurement of Potential Differences 107 (b) Procedure in Making Measurements of Potential Differ- ences 107 B. Current Surveys. 1. Scope and Importance of Current Surveys 108 2. Measurement of Currents in Feeders and Rails 109 (a) Purpose of Measuring Feeder and Rail Currents 109 (b) Procedure in Measuring Current in Feeders and Rails . 109 3. Measurement of Currents in Pipes and Cable Sheaths 110 (a) Purpose and Importance of Pipe Current Measurements. 110 (b) Selection of Points of Measurement 110 (c) Methods of Measuring Current Flow in Pipes Ill Drop in Potential Method 113 Qalibration of Pipes 113 Use of a Direct-Current Ratio Relay 115 4. Comparing Currents Under Different Conditions 115 CONTENTS II Page 5. Measurement of Current Flowing from Underground Struc- tures to Earth 115 (a) Differential Current Measurements 116 C. Miscellaneous Tests. 1. Track Testing 116 (a) Inspection 116 (b) Use of Portable Bond Tester '. . 117 (c) Autographic Method of Bond Testing 117 (d) Testing of Cross-bonds and Special Work 117 2. Measurement of Leakage Resistance Between Tracks and Underground Structures 119 (a) Importance of Tests of Roadbed Resistance 119 (b) Differential Method of Measuring Roadbed Resistance. 119 (c) Isolation Method of Measuring Roadbed Resistance. . . 121 3. Location and Testing of High Resistance Joints in Pipes 122 4. Tracing the Source of Stray Currents 123 5. Location of Unknown Metallic Structures or Connections. . . 123 III. INTERPRETATION OF RESULT^ OF ELECTROLYSIS SURVEYS A. Interpretation of Potential Measurements. 1. Maximum Voltages and Track Gradients 124 2. Potential Difference Measurements 125 B. Interpretation of Current Measurements on Underground Structures. 1. Relation of Stray Current to Corrosion 125 2. Relation of Current to Fires and Explosions 126 C. Interpretation of Measurements of Current Flowing from Structures to Earth 126 D. Use of Reduction Factors 127 E. Effect of Reversals of Polarity. 1. Polarity of Pipes Always the Same 128 2 . Polarity of Pipe Changing with Long Periods of Several Hours. 128 3. Polarity of Pipes Reversing with Periods of Only a Few Minutes 128 4. Polarity of Pipes Reversing with Periods of From Fifteen Minutes to One Hour 129 IV. SELECTION OF INSTRUMENTS A. Portable Measuring Instruments 129 B. Recording Instruments 130 V. RECORDS AND REPORTS: A. General Discussion : . . . 131 B. Electric Railways 131 C. Piping Systems 132 D. Cable Systems 132 E. Bridges and Buildings 132 F. General Conditions 132 VI. TABLES... . 133 12 CONTENTS Page CHAPTER 4. European Practice A. General 134 B. Laws and Regulations. 1. Germany 135 (a) Commission Recommendations 136 2. Italy 136 3. France 136 4. Spain 137 5. Great Britain 137 C. Construction Characteristics. 1. General 138 2. Rails 140 3. Rail-Bonds 141 Table 7. Rail Bonding (United Kingdom) 143 4. Cross-Bonds 143 5. Roadbed Construction 143 6. Feeders. . '. 147 7. Negative Boosters 148 Table 8. Use of Negative Boosters (United Kingdom) 148 8. Double Trolley 149 9. Three-wire System 1 49 10. Negative Trolley 149 11. Pilot Wires 150 12. Bond Testing . . . 150 13. Pipes and Pipe Joints 150 14. Depth of Pipes Below Surface 150 15. Mains on Both Sides of Streets 151 16. Insulating Coverings for Pipes 151 17. Electric Cables 151 D. Electrolysis Conditions. 1. General 151 2. Voltage and Current Conditions : Experience with Electrolysis. 152 (a) Germany 152 (b) Italy 153 (c) France 153 (d) Great Britain 154 E. Miscellaneous Observations. 1. Drainage System 155 2. Corrosive Effects of Soil; Earth Resistance 155 3. Electrolysis Testing Methods 156 4. Economic Aspects of the Electrolysis Problem 157 5. Application to American Conditions , 157 F. Summary 158 G. European Regulations Adopted and Proposed. Germany 159 Sec. 1. Application of Rules 159 Sec. 2. Rail Conductors 162 Sec. 3. Rail Potential 165 Sec. 4. Resistance between Rail and Earth .. . 170 CONTENTS 13 Page G. European Regulations Adopted and Proposed (continued) Germany (continued) Sec. 5. Current Density 172 Sec. 6. Control 175 France 176 England 177 Spain 183 CHAPTER 5. Electrolysis Research Further Work Necessary to Arrive at a Solution of the Engi- neering Problem. 1. Methods of Testing '. . 184 2. Effect of Different Rail Voltage Drops 185 3. Studies of Electric Railway Power Distribution 185 4. Study of Mitigative Measures Applicable to Affected Struc- tures 185 5. Determination of Safety Criterion for Pipes Where Positive to Earth 185 6. Self Corrosion 186 7. Fire and Explosion Hazard on Gas and Oil Pipes 186 8. Heating of Power Cables Due to Stray Currents on Sheaths. 186 Summary 187 BIBLIOGRAPHY General 188 Electrolytic Corrosion of Pipes and Cables 188 Surveys and Measurements 189 Alternating Current and Periodic Current Electrolysis 189 Reinforced Concrete 189 Track Construction, Track Leakage, and Rail Bonding 189 Insulated Negative Feeders 190 Automatic Substations 190 Three-Wire Operation 191 Insulating Pipe Coverings 191 Insulating Joints 191 Pipe and Cable Drainage 191 Legal Aspects 192 APPENDIX Tables of Current Data for Rails and Pipes 193 Sample Data Sheets 200 LIST OF ILLUSTRATIONS Page Figure 1. Single Trolley Electric Railway Showing Paths of Return Current 35 Figure 2. Potential Profile of Railway System 36 Figure 3. Potential Profile Showing Rails and Pipes without Connec- tions Between Pipes and Railway Return Circuit 37 Figure 4. Effect of Feeding Distance on Stray Current 39 Figure 5. Effect of Feeding Distance on Overall Voltages and Poten- tial Difference Between Earth and Rails 40 Figure 6. Reduction of Track Voltage Drop by Additional Power Sup- ply Stations 41 Figure 7. Relation of Number of Substations to Annual Charges, for Interurban Line 43 Figure 8. Potential Profile of Two Independent Railway Systems Showing Effect of Interconnection 48 Figure 9. Overall Voltage Curves, No Feeders 50 Figure 10. Equi-Potential Insulated Negative Feeder System 50 Figure 11. Insulated Negative Feeders Applied to City Net- work of Tracks 52 Figure 12. Graded Insulated Negative Feeder System 54 Figure 13. Insulated Negative Feeders Applied to Interurban Lines. . . 56 Figure 14. Parallel Three-Wire System ' 58 Figure 15. Sectionalized Three-Wire System .- . . . 58 Figure 16. Variation of Coefficient of Corrosion of Iron with Frequency. 64 Figure 17. Cross-Section of Insulating Joint for Power Cable Sheaths. 72 Figure 18. Showing Necessity of Installing Insulating Joints in Services Connected to Mains Laid with Insulating Joints 75 Figure 19. Type B Bell for Cast Iron Pipe, Designed for Cement Joints . 77 Figure 20. Service Pipes Being Damaged Under Car Tracks by Elec- trolysis 80 Figures 21 and 22. Methods of Installing Leads for Current Test Station 112-114 Figure 23. Differential Method of Making Roadbed Resistance Meas- urements 118 Figure 24. Method of Making Roadbed Resistance Measurements on Open Track Construction 120 Figure 25. German Tramway Rails 139 Figure 26. British Tramway Rails 140 Figure 27. Rail Weight Data 141 Figure 28. Typical Rail Bonds United Kingdom 142 Figure 29. Cross-Bonding Details, etc. United Kingdom ." 144 Figure 30. Track Construction United Kingdom 145 Figure 31. Track Construction and Rails Germany 146 Figures 32 and 33. Key to Calculation of Voltage Drop in Rails 168 14 CHAPTER 1 PRINCIPLES AND DEFINITIONS A. ELECTROLYSIS IN GENERAL. 1. Electrolysis is the process whereby an electric current pass- ing from an electrode to an electrolyte or vice versa causes chemical changes to take place in the electrolyte. Electrolysis also in- cludes any chemical changes at the surface of an electrode re- sulting from the chemical changes in the electrolyte. Electrolysis is independent of the heating effect of the electric current. NOTE. These changes usually occur in a water solution of an acid, alkali, or salt. By the passage of an electric current through it, water (containing a trace of acid) is decomposed into hydrogen and oxygen, copper is deposited from a solution of copper sulphate, silver from solutions of silver salts. Electroplating, electrotyping, and refining of metals by electrodeposition are useful applications of electrolysis in the arts. Electrolysis is involved in the charge and discharge of storage batteries, and in the operation of primary batteries. In order that electrolysis may occur, the following condi- tions must be present : (a) There must be a flow of electric current through a conducting liquid from one terminal to another ; (b) The conducting liquid must be a chemical compound or solution which can be altered by the action of the electric current. 2. Electrolyte, Electrode, Anode, Cathode. The electrolyte is the solution (or fused salt) through which the electric current flows; the conducting terminals are the electrodes; the terminal by which the current enters the solution is the anode; the terminal by which it leaves is the cathode. NOTE. The chemical changes caused by the current may affect both the electrolyte and the electrodes. In the case of a solution of copper sulphate with copper plates as elec- trodes, copper is removed from the anode by the current and carried into solution; an equal amount of copper is deposited upon the cathode. In general the metal travels with the current toward the cathode. 3. Amount of Chemical Action. (Faraday's Law.) The amount of chemical action taking place at the anode and also at the cathode (as expressed by Faraday's Law) is proportional to (1) the strength 15 16 PRINCIPLES AND DEFINITIONS of current flowing, (2) the duration of the current, and (3) the chemical equivalent weights of the substances. NOTE. Otherwise expressed, the quantity of metal or other substance separated is proportional to the total quantity of electricity passing and the electro-chemical equivalent of the substance or substances concerned. The electro-chemical equivalent of a metal is proportional to its atomic weight divided by its valence. Faraday's Law is so exactly realized in practice under favorable conditions that it is used as the basis for the definition of the international ampere, one of the fundamental electrical units. (See Passivity, Paragraph 15.) 4. Cause of Current Flow. The current flowing through the electrolyte may be due (1) to an external electromotive force or (2) to the difference of potential due to the use of electrodes of different materials or to solutions of different concentrations. NOTE. The first case is illustrated by electrolysis of dilute sulphuric acid using two lead plates and an external battery; the second by the electrolysis of the same solution using a zinc and a copper plate, which touch each other inside or outside the solution. The first occurs in charging a storage battery; the second in the discharging of a primary battery or a storage battery. 5. Electrolysis by Local Action. Instead of two plates of different metals the same result may follow with one plate if it is chemically impure or otherwise heterogeneous, when immersed in an electrolyte. NOTE. Such a plate excites local currents and a loss of metal occurs at all the anode areas. This local action causes impure zinc to dissolve rapidly in a solution which has no action on pure zinc. 6. Anodic Corrosion is the term applied to the loss of metal by electrolysis at the anode. NOTE. When iron is anode the iron is carried into solu- tion by the current, the first product being a salt of iron, the nature of which depends upon the character of the electrolyte. In dilute sulphuric acid, ferrous sulphate is formed ; in hydro- chloric acid, ferrous chloride, etc. These first products of electrolysis are frequently modified by secondary reactions. 7. Secondary Reactions are the chemical changes which occui at or near the electrodes, by which the primary products of elec- PRINCIPLES AND DEFINITIONS 17 trolysis are converted into other chemical substances, and are sometimes followed by other reactions. NOTE. Ferrous hydroxide formed by the union of iron with hydroxyl ions set free at the anode, is subsequently converted into iron oxide due to the reactions with oxygen dissolved in the electrolyte. When lead is cathode in an alkali soil or solution, the alkali metal (such as sodium or potassium) reacts with water at the cathode and forms alkali hydroxide, setting hydrogen free. This hydroxide may react with the lead chemically and form lead hydroxide (especially after the current ceases), which in turn may com- bine with carbon dioxide, forming lead carbonate. 8. Calhodic Corrosion is the term applied to the corrosion due to the secondary reactions of the cathodic products of elec- trolysis, as described in the preceding paragraph. The metal of the cathode is not removed directly by the electric current but may be dissolved by a secondary action of alkali produced by the current. NOTE. The anodic corrosion is more common and more serious; cathodic corrosion, however, sometimes occurs on lead and other metals that are soluble in alkali. Cathodic corrosion never occurs in the case of iron. B. ELECTROLYSIS OF UNDERGROUND STRUCTURES. 9. General. As used in this report, the term "electrolysis" embraces the entire process of accelerated corrosion of under- ground metallic structures due to stray current. In the electrol- ysis of gas arid water pipes, cable sheaths, and other underground metallic structures, and the rails of electric railways, the moisture of the soil with its dissolved acids, salts, and alkalis is the electro- lyte, and the metal pipes, cable sheaths and rails are the electrodes. NOTE. Wherever the current flows away from the pipes they serve as anodes and the metal is corroded. Metal or gas or alkali, according to the nature of the soil, will be set free at the cathode. . 10. Self Corrosion is the term applied when a pipe or other mass of impure or heterogeneous metal buried in the soil is corroded due to electrolysis by local action. NOTE. This is called "self corrosion" because the electric current originates on the metal itself, without any external agency to cause the current to flow. Self corrosion may also be due to direct chemical action. 11. Acceleration of Local or Self Corrosion. Self corrosion is accelerated by the presence in the soil water of acid or salts which 18 PRINCIPLES AND DEFINITIONS lower its resistance as an electrolyte, and also by cinders, coke or some other conducting particles of different electric potential which augment the local electric currents. In the latter case the metal need not be heterogeneous. NOTE. A pipe may be destroyed in a relatively short time by self corrosion or local action if buried in wet cinders or in certain soils. 12. Stray Current is that current which has leaked from the return circuit of an electric railway system and flows through the earth and metallic structures embedded therein. 13. Anodic and Self Corrosion. Anodic corrosion due to stray currents and self corrosion due to local action may occur simul- taneously, and the former may accelerate the latter. NOTE. Hence the corrosion due to a given current plus the increased self corrosion induced by that current may give a greater total corrosion than called for by Faraday's Law. This explains how the coefficient of corrosion may exceed unity. 14. Coefficient of Corrosion. The coefficient of electrolytic corrosion (sometimes called corrosion efficiency) is the quotient of the total loss of metal due to anodic corrosion (after deducting the amount of self corrosion if any) divided by the theoretical loss of metal, as calculated by Faraday's Law, on the assumption that the corrosion of the anode is the only reaction involved. NOTE. In practice it is found that the coefficient of corrosion varies widely from unity, being sometimes as low as 0.2 and sometimes even above 1.5, but commonly between 0.5 and 1,1. 15. Passivity is the name given to the phenomenon in which a current flows through an electrolyte without producing the full amount of anodic corrosion which would occur under normal conditions. NOTE. This restricted definition of passivity has regard only to its effect in electrolysis. Many conditions affect the degree of passivity attained, an initial large current den- sity being favorable to it. Plunging iron into fuming nitric acid renders it temporarily passive. A satisfactory explana- tion of passivity has not been given. 16. Polarization Voltage (sometimes called polarization poten- tial) is the temporary change in the difference o'f potential "between an electrode and the electrolyte in contact with it due to the PRINCIPLES AND DEFINITIONS 19 passage of a current to or from the electrode. This change in potential difference is due to the change in the conditions of the surface of the electrode or change in the concentration of the electrolyte (or both), and under some conditions is approximately proportional to the current flowing, but in many cases is not so proportional. The magnitude of the polarization voltage also depends on the material of the electrode, the nature of the electro- lyte, and the direction of the current. 17. Alternating or Frequently Reversing Direct Currents. If alternating currents (or frequently reversing direct currents) flow through the soil between pipes or other underground metallic structures, the metal removed during the half cycles when a pipe is anode may be in part replaced when it is cathode. Hence, the total loss of metal on a given pipe may be less than is indicated by computing the loss on the basis of the positive part of the cycle only, and in the case of alternating current at commercial fre- quency may be less than 1% of such computed values. NOTE. In slow reversals of current the recovery effect is less, but the loss will be less than with direct current con- tinuously in the same direction (excepting possibly where the phenomenon of passivity may affect the result). 18. Action on Underground Metallic Structures. Faraday's Law applies to electrolysis of metallic structures in soil as else- where, the total chemical action being proportional to the average current strength and the time the current flows and to the elec- trochemical equivalent of the metal of other substances concerned. Although local action and passivity affect the loss of metal and so apparently modify Faraday's Law, it is still true that the total chemical action resulting from the current flow is proportional to the total current when local currents are included. NOTE. Sometimes this chemical action is concerned only with corroding the anode; sometimes it is concerned with breaking up the electrolyte, as when the anode is a noble metal or in the passive state (as iron and lead sometimes are) : sometimes both these effects occur. The theoretical loss of iron per year per ampere is about twenty pounds and of lead is 3.7 times this amount or about seventy-four pounds. The loss in volume of lead is 2.4 to 2.6 times that of iron. The greater loss in lead is due to the higher electrochemical equivalent of that metal. 19. Electrolysis Mitigation. The two primary features of electrolysis mitigation are (1) the reduction of the flow of current 20 PRINCIPLES AND DEFINITIONS through the earth and the metallic structures buried in the earth, (2) the reduction of the anode areas of such structures to a mini- mum, where the current is not substantially eliminated in order to reduce the area of destructive corrosion as far as possible. NOTE. The current in the underground metallic structures will be decreased, other conditions remaining the same, by (1) increasing the conductance of the return circuit, (2) increasing the resistance of the leakage path to earth, (3) increasing the resistance between the earth and the under- ground metallic structures, (4) increasing the resistance of the underground metallic structures. The anode areas of the underground metallic structures will be decreased, other conditions remaining the same, by providing suitably placed metallic conductors for leading the current out of the underground structures so that the flow of the current directly to the earth shall be minimized. This will change a portion of the anode area to cathode. 20. Electrolysis Survey. An electrolysis survey is the opera- tion of determining by means of proper measurements all relevant facts pertaining to electrolysis conditions, such as the voltage drop in the grounded railway return; the location and extent of the areas in which the metallic structures are in danger from stray currents; the condition of the structures and adjacent soil in the danger areas, and the extent of any damage that may have occurred; the seriousness of electrolytic action in progress and the source of the stray current producing the damage, its course and magnitude and the conditions in neighboring structures tending to produce electrolysis. If will generally be found desirable to make some preliminary tests for the purpose of indicating the lines along which the complete survey should be made. 21. Overall Potential Measurements. Overall potential meas- urements are measurements which are made to determine the difference in electric potential between points in the tracks at the feed limits of the station and the point in the tracks which is lowest in potential, and are obtained by means of pressure wires and indicating or recording voltmeters. This is most commonly applied to measurements of voltage between the point of lowest potential in the grounded portion of a railway return system and the points of approximately highest potential on its various branches. 22. Potential Gradient. A potential gradient is the voltage drop per unit of length between two points on a single conductor PRINCIPLES AND DEFINITIONS 21 or in the earth, and is usually expressed in volts per thousand feet. 23. Potential Difference. In electrolysis work the term "potential difference" usually means the difference in potential which exists between nearby points on separate systems of con- ductors, or between conductors and the earth, e.g., between pipes and rails, lead sheaths and rails, lead sheaths and earth, etc. 24. Arithmetical Average. The arithmetical average value of a current or potential is the average value of all the instantaneous values of the same polarity. 25. Algebraic Average. The algebraic average value of a current or potential is the algebraic sum of all the instantaneous values, divided by the number of such values. 26. Positive and Negative Areas. Positive areas are those areas where the current is in general leaving the pipes or other underground metallic structures for the earth. Such areas are often called danger areas. Negative areas are those areas where the current is in general flowing to the pipes or other underground metallic structures. NOTE. As the current often flows from one underground metallic structure to another, it is evident that within a positive area there are local negative areas and vice versa. Hence the terms are applied somewhat loosely, and according to which condition predominates. Besides the positive and negative areas there are areas of more or less indefinite extent in which the current flow between metallic underground structures and earth normally reverses between positive and negative values. These areas are called neutral areas or neutral zones. 27. Drainage System. A drainage system is one in which wires or cables are run from a negative return circuit of an electric railway and attached to the underground pipes, cable sheaths or other underground metallic structures which tend to become positive to earth, so as to conduct current from such structures to the power station, thereby tending to reduce the flow of current from such 'structures to earth. NOTE. Three kinds of drainage systems may be distinguished : (1) where direct ties with wires or cables are made between underground metallic structures and tracks, (2) where un- insulated negative feeders are run from the negative bus to underground metallic structures, (3) where separate insulated 22 PRINCIPLES AND DEFINITIONS negative feeders are run from the negative bus to underground metallic structures, or a main feeder with taps to such structures. 28. Uninsulated Track Feeder System. An uninsulated track feeder system is one in which the return feeders are electrically in parallel with the tracks. Under such circumstances the cables may be operating very inefficiently as current conductors and as a means of reducing track voltage drop, particularly where voltage drops in the grounded portion of the return are maintained at the low values usually required for good electrolysis conditions. (See Chapter 2, Reinforcement of Rail Conductivity.) 29. Insulated Negative Feeder System. An insulated negative feeder system, sometimes called an insulated return feeder sysem, or insulated track feeder system, is one in which insulated wires or cables are run from the insulated negative bus in a railway power station and attached at such places to the rails of the track as to take current from the track and conduct it to the station in such a manner as to reduce the potential gradients in the tracks and the differences of potential between underground metallic structures and rails, thereby reducing the flow of current in underground metallic structures. (See Chapter 2, Insulated Negative Feeder System.) NOTE. The insulated negative feeders may run separately from the negative bus to various points in the track network, or a smaller number of cables may be used with suitable resistance taps made to tracks at various places. With this system the drop of potential in the track feeders is independent of the drop of potential in the tracks. CHAPTER 2 DESIGN, CONSTRUCTION, OPERATION AND MAINTENANCE The practical electrolysis problem is due to stray current from electric railways. Instances of stray direct currents from other sources sometimes occur, but such cases are not specifically considered in this report. Currents straying to earth from electric railway tracks frequently find their way to water and gas pipes, telephone and power cables, and other underground structures. When this current leaves these structures through earth, corrosion results. Thus not only are the structures of many different companies subject to injury, but by reason of the different public services dependent on such structures, the public as a whole has a direct interest in this type of electrical interference. The problem, therefore, is one which is preeminently adapted to cooperative treatment. In many cities it has been found advantageous to form joint committees, composed of technical representatives of the several utilities concerned, to investigate the local electrolysis situation and determine by agreement a course of procedure to be followed. Such committees should attack the problem in an open and fair- minded manner with the object of effecting, in the most economical way, mitigation of all the troubles resulting from the presence of stray currents in the earth, including corrosion, fire and explo- sion hazards, heating of power cables, and operating losses and difficulties. To this end, they should be composed of men, or have men associated with them, who are trained in the technique of electrolysis. Active committees of the kind described are now existent in Chicago, Kansas City, Omaha, St. Paul, New Haven, Milwaukee, and Syracuse. The principle of cooperation has been recognized by the Railroad Commission of Wisconsin in an order authorizing an Electrolysis Committee in the City of Mil- waukee. Such committees act as clearing houses of information and keep all the interested companies informed as to changes in their systems which may affect the electrolysis situation. Under the direction of such a committee joint electrolysis surveys may be conducted and unified methods of mitigation installed and maintained. The magnitude of stray currents is determined by the design, construction, maintenance, and operation of the railway system. 23 24 DESIGN, CONSTRUCTION, OPERATION, ETC. In general, the same factors that determine the amount of stray currents are those that have a direct bearing on the economy of railway operation. A good example is that of an insufficient number of substations, which results both in large stray currents and poor railway economy. Similar results follow from defective bonding, rails of inadequate size, or failure to interconnect tracks. For this reason, it is believed that many existing railway systems can be modified in such a way as to increase their own economy of operation, while at the same time securing important reduction in stray current. Measures of this character, which are essential to the most economic operation of the railway, should be regarded as a prerequisite of the application, either to the railway or to the affected structures, of measures specifically for electrolysis mitigation. Prior to the consideration of measures of electrolysis mitiga- tion, the following features should be given due attention : 1. Measures Tending Both to Railway Economy and the Reduc- tion of Stray Current. (a) The return system, including track bonding, should be put in proper condition. (b) The number of substations should be made a maximum consistent with railway economy. 2. Measures Employed Solely for Electrolysis Prevention. Where necessary to effect a still further reduction in electrolysis below that provided by the most economic railway system one or more of the following measures should be taken : (a) Applicable to Railways. (1) Additional substations, (2) Insulated negative feeders, (3) A modified system of power dis- tribution such as a three-wire system. (b) Applicable to Affected Structures. (1) Insulating joints in pipes and cables, (2) Insulating coverings for pipes. (c) Interconnection of Affected Structures and Railway Return Circuit. (1) Electrical drainage of cable sheaths, (2) Electrical drainage of pipes. DESIGN, CONSTRUCTION, OPERATION, ETC. - 25 I. RAILWAYS A. FEATURES WHICH AFFECT ELECTROLYSIS CONDITIONS 1. Track Construction and Bonding. (a) Importance of Rail Circuit. Stray current is increased by A [ insufficient rail weights and imperfectly bonded track joints, p While the major portion of the current of a grounded return railway generally returns through the tracks and return feeders to the power station, a portion finds a parallel path through the earth and its buried metallic structures. As the current flowing in each path is inversely proportional to the resistance of that path, it is of prime importance to make the resistance of the track circuit as low as possible by the use of rails of adequate weight . and proper bonding. (b) Rail Bond Resistance and Tests. The contact resistance of the bond terminal connection to the rail may be a considerable part of the resistance of the joint if the bond is not properly installed and maintained and it is therefore essential in selecting the type of bond to be used, that special consideration be given this feature. It is the usual practice to measure the resistance of the bonded joint including three feet of rail in terms of a length of continuous rail. The equivalent length of a properly bonded joint including three feet of rail, varies from 3 to 6 feet, depending upon the size of the rail, and the type, length and cross sectional area of the bonds. On some electrified steam roads it is the practice to bond so that the joint alone will have an equivalent resistance of 20 || inches of continuous rail and to rebond when this resistance " increases to 42 inches. On street railway systems bonding to an equivalent length of 3 to 6 feet is common practice where short .bonds are used, rebonding when the joint resistance including three feet of rail increases to that of 10 feet of rail. A single No. 0000 long bond, installed around the splice plates will have with three feet of rail, a resistance equivalent to from 8 to 15 feet of continuous rail, depending upon the size of the rail. Practice varies widely as to the frequency of testing rail bonds but most railway companies make complete tests of all bonds at least once each year and more frequent tests on tracks subject to excessive traffic or deterioration. Good practice would require annual tests of all bonds, and semi-annual on tracks in which the bond failures exceed five per cent annually. 26 DESIGN, CONSTRUCTION, OPERATION, ETC. (c) Types of Bonds. Bonds may be classified according to the method of fastening them to the rails as follows : (1) Soldered. (2) Brazed or Welded. Resistance Weld. Electric Arc Weld. Oxy-Acetylene Weld. (3) Pin Expanded. (4) Compressed Terminal. Solid Single Terminal. Single or Multiple Stud. There is a further distinction between exposed and concealed bonds, the latter being used where the prevention of theft is a serious consideration, in which case the bonds are installed under- neath the splice plates. Local conditions will largely determine the type of bonding to be used. Consideration should be given to the economy of construction, maintenance, costs, facilities for using bonding equipment, tools, etc. In recent years there has been a marked tendency toward the more general use of all types of welded bonds with almost complete abandonment of soldered bonds and those mechanically applied to the head of the rail. Pin-terminal and compressed-terminal bonds are still extensively used for applica- tion to the web of the rail but even here the welded type is finding favor with many companies. One reason for the increasing use of oxy-acetylene and electric alloy welded bonds is to be found in the lighter, cheaper, and more portable tools for their applica- tion, some of the newer methods and apparatus which have been developed for this class of work being far superior to those formerly employed. Soldered Bonds are applied to the head, base or web of the rail by means of solder, a blow torch being used to heat the rail" to a soldering temperature. The difficulty of securing a permanent and low resistance contact has caused practically all railway companies to abandon this type of bond. Brazed or Welded Bonds are applied either by the use of the heating effect of an electric current or arc or an oxy-acetylene gas flame. . The Resistance Weld of bond to rail is accomplished by clamping a carbon block against the head of the bond and heating this block to a high temperature by the passage of a large electric current or by drawing an arc on the face of the block. DESIGN, CONSTRUCTION, OPERATION, ETC, 27 In the Electric Arc process the arc is drawn directly on the rail and bond terminal. In both the resistance and arc methods of welding or brazing the rail and bond terminals are brought to a welding or brazing heat and united in a solid mass by filling in metal, thus forming a mechanical and electrical union. The filling in metal may be a copper or iron wire used as an electrode. When the bond terminal is steel, the latter metal is used. Several methods, differing somewhat in the equipment used and the methods of applying the heat to the bond and rail, are in use, and the selection of the most suitable of these will depend upon a number of factors and often upon local conditions. The Oxy-Acetylene process is similar to arc welding except that the heating is accomplished by means of an oxy-acetylene gas flame from a blow torch. These methods give a connection of low resistance and short t\ bonds can be applied to the head of the rail without much danger \ \ of theft due to the small amount of copper involved and the tenacious contact between bond and rail. Pin Expanded Terminal Bonds have a hole in each terminal through which a tapered drift pin is driven to expand it into a hole drilled in the web of the rail after which a pin, slightly larger than the drift pin, is driven into the hole and left there to prevent contraction. This type of bond requires great care and accuracy in manufacture and in installation, but when properly installed makes a very efficient and satisfactory construction. The essential features are a carefully and accurately milled termi- nal and a perfectly clean, circular-drilled hole, reamed to proper diameter, in the rail. Care should be used to brighten the terminal with emery paper just before installing and to avoid contact with the fingers which will cause corrosion between the terminal and the rail. Holes should be drilled dry and bonding should not be done except in fair weather so there will be no moisture to induce corrosion. This type of bond is usually applied to the web of the rail. As it requires only small portable tools it has been found to be particularly well adapted to main line tracks under operating conditions. Compressed Terminal Bonds are of two kinds, one being a single solid terminal bond applied to the web of the rail in a manner similar to the Pin Expanded Terminal bonds described above except that contact with the rail is secured by means of a heavy screw or hydraulic compressor applied to each end of the terminal, causing it to compress longitudinally and expand laterally, bringing 28 DESIGN, CONSTRUCTION, OPERATION, ETC. the copper into firm contact with the steel. The screw compressors used for compressed terminal bonds are objectionable where fast traffic is maintained on the tracks as they clamp over the head of the rail, making a dangerous condition due to the possibility of causing derailment. The other is a single or multiple stud terminal bond applied to the head of the rail, the terminal studs being set in holes and expanded into contact by hammer blows. This type of bond has been largely superseded by the modern types of brazed- and welded head bonds. (d) Welded Rail Joints. The difficulties and uncertainties attending the proper maintenance of rail joints and bonds have been eliminated to a large degree by the successful use of several modern types of welded joints, such as electric resistance and arc welding, cast welding, and thermit welding. The welded joint in one form or another has been adopted as a standard of con- struction in nearly every large city in the United States. Most types of welded joints have a conductivity equal to or greater than the continuous rail and are less subject to failure than any form of rail bond. They must be considered, therefore as a most important factor in the reduction of stray current. Electric Rail Welding is performed by clamping heavy iron bars to the web of the rail and bringing the bars and the adjacent rail to a white heat by means of an electric current. The process requires a heavy and expensive plant and is usually carried out by contract on a comparatively large scale. For this reason it is not well suited to installations on small systems. It is well adapted to the reclaiming of old track as well as for new work and has been applied on open T-rail construction where expansion joints are installed at intervals to provide for expansion and contraction. Arc Welding. There are several forms of arc welding where the splice bars are welded to the rail at a number of points by the use of an electric arc. Electric arc welding may be done under traffic conditions and is more extensively used in maintenance work than other methods. Cast Welding is accomplished by setting a mould around the rail joint and pouring molten iron from a crucible around the joint. This process requires transporting a portable cupola along the street adjacent to the work. On account of the improvement in similar types of joints with more portable equipment, this method is not now used as much as formerly. The Thermit process is a modification of the cast weld, the iron being liberated at white heat from a mixture of iron oxide and DESIGN, CONSTRUCTION, OPERATION, ETC. 29 aluminum, which is ignited in a crucible. Cast welding is used chiefly on new construction and cannot be done under traffic. The renewal of a cast weld joint requires cutting in a short length of new rail which adds another joint to the track. (e) Cross-bonding. The important objects of cross-bonding are to equalize the current flow between the rails, thus reducing the voltage drop and also to insure continuity of the return circuit in case of a broken length of rail or a broken bond in any rail. It is good practice to place cross-bonds at intervals of 1,000 to 2,000 feet on suburban railways and not to exceed 500 feet on urban rail- ways. Cross-bonding between parallel tracks is in some cases installed with the same frequency as between .the rails of the single track; in other cases at less frequent intervals. Some companies make a practice of installing cross-bonds under each feeder tap to the trolley wire or at every fourth or fifth span wire, thus enabling them to conveniently preserve a record of their locations. In cases where the track has been carefully insulated cross-bonds should preferably be rubber insulated so as to in- crease their electrical resistance to earth, and where subject to damage from track tools and to other mechanical injury the insu- lation should be protected by circular loom or conduit. The common practice of electrified steam railroads is to use cross-bonds with a conductance equal to one track rail, or of about 1,000,000 circular mils cross-section. Street and inter- urban railways employ bonds having a cross-section of from 200,000 to 500,000 circular mils. (f) Special Track Work Bonding. It is good practice to pro- vide jumpers at switches, frogs and at other special track work to insure that the electrical continuity of the bonded rail will be maintained. This is usually accomplished by jumpers extending around the special work, and in such cases the frogs are bonded into the track system, or where practicable the special work is bonded as other track rails. The size of the jumper cables to be used will depend upon the nature of the traffic. On tracks bearing heavy traffic a separate cable is usually provided for each rail, while for light traffic a single jumper connecting to all rails on both sides of the special work is sometimes used. In all cases the jumpers should be proportioned to the current carried in the track and in no case less than a No. 0000 for one track. In cases where the track has been carefully insulated the best practice provides for the use of insulated cables for jumpers, except in dry locations, as for instance, on bridges or on other 30 DESIGN, CONSTRUCTION, OPERATION, ETC. elevated structures where the ties are not in contact with earth or ballast. The electrical leakage from one bare track juniper to damp earth has been known to offset the effect of many miles of most careful track insulation. Under such conditions, if positive to the earth, the bond is gradually destroyed by electrolysis. (g) Bonding Tracks with Signal Systems. In determining the location of cross-bonds and jumpers in connection with alternating current track signal circuits, a departure from ideal spacing becomes necessary, owing to the fact that cross-bonds are per- missible only at the reactance bonds. The signal reactance bonds are located between the signal block sections, and these sections are more or less fixed for train operating conditions. The method used where tracks carry heavy currents is to cross- bond at all signal reactance bonds and install additional cross- bonds with reactance bonds at intermediate locations to obtain the most satisfactory resistance conditions in the sections fixed by the signal system. (h) Conductivity and Composition of Rails. The conductivity of the track rails used by several interurban and electrified steam railroads has been found to be equivalent to about Jfi that of copper, and this figure generally holds approximately true for girder types of rails, except when alloy steel is used, in which case higher resistivities are found. The track rails are specified for their mechanical qualities, and where these interfere with the electrical requirements, it is customary to give the mechanical qualities preference. The composition of rails for heavy service used by one of the large electrified steam railroads, in percentage, is as follows : Carbon 0.62 to 0.75 Manganese 0.70 to 1.00 Silicon 0.10 to 0.20 Phosphorous Not to exceed . 04 The American Railway Engineering Association has adopted the following composition for heavy rails : Class A Rails Class B Rails Carbon 0.60 to 0.75 0.70 to 0.85 Manganese. 0.60 to 0.90 0.60 to 0.90 Silicon Not more than 0.20 Not more than 0.20 Phosphorous Not more than 0.04 Not more than 0.04 DESIGN, CONSTRUCTION, OPERATION, ETC. 31 2. Track Insulation. (a) Degrees of Insulation. Under this sub-heading have been considered, (1) Substantial Insulation, in which the type of con- struction largely prevents the escape of stray current, and (2) Partial Insulation, which comprises using such means as are avail- able to insulate from the earth the running rails of ordinary street railways insofar as practicable. Substantial Insulation. Interurban and electrified steam roads generally require the rail to be supported on wooden ties set in well drained broken stone or gravel ballast. Such construction affords a very high resistance between the tracks and earth and reduces the danger of electrolysis to a minimum. With 10 volts between rail and ground the leakage in some instances is found to be as low as 0.00016 amperes per rail per tie under dry weather conditions, increasing to 0.0055 amperes when wet. On double track with ties spaced 2 feet apart these values represent 0.32 and 11.0 amperes, respectively, per 1,000 feet, or 31 and 0.91 ohms respectively for 1,000 feet. On steel structures where the ties are only partially in contact with the ground and cannot become waterlogged, this leakage is even less. The substantial insulation of a ballasted roadbed has, in some installa- tions, been rendered ineffective by bare negative cables in damp earth or by metallic connections between the tracks and steel supporting structures. Conditions are found to be very favorable for rail insulation where the tracks are in subways or under cover protected from the weather, permitting the ballast and ties to become permanently dry. Partial Insulation. Tracks placed in city streets where rails are depressed to the surface of the ground and have only their upper surface exposed can be but partially insulated. The character of the material in immediate contact with the rails has a large influence on the resistance to ground, but it has been repeatedly demonstrated that coating the rails with an insulating material is not advisable, and the best plan is to provide a roadbed, which, taken as a whole, is of an insulating character. The use of well drained broken stone or gravel ballast results not only in a good roadbed, but also affords a much higher resistance to the escape of stray current than does a roadbed of concrete. It is desirable to keep vegetation down and otherwise keep the ballast dry and prevent foreign material from washing into it. Salt, which is frequently used to prevent freezing at switches and 32 DESIGN, CONSTRUCTION, OPERATION, ETC. frogs, greatly increases the conductivity of the roadbed and thereby facilitates the escape of stray current. Electric railways have experienced some damage due to the corrosion of the base of the rail or of elevated structures connected to the rails in districts where the stray current leaves the structure for the earth. Cases are on record where this corrosion is serious and where steps have been taken to reduce the damage to elevated structures by insulating the rail from the steel structure. Any measure which tends to insulate the track from the soil or any mitigative system which tends to reduce stray current will tend to retard the electrolytic corrosion of the base of the rails and other grounded steel structures. (b) Leakage to be Expected. Under conditions of substantial insulation and where the roadbed is of open construction the leakage varies widely depending upon the character of the ballast and whether it is wet or dry. In dry weather the resistance may be from 10 to 15 ohms or even more per 1,000 feet of single track. In wet weather this may drop to 3 to 5 ohms. If ties are treated with a 3 to 1 mixture of gas oil and creosote, the resistance may be double the above values whereas with ties treated with zinc chloride or other chemical salts the resistance may be one-half of these values. The leakage where tracks are only partially insulated will not only be much greater than where they are substantially insulated but will vary over a much wider range. This is because the type of roadbed, character of soil, and drainage conditions vary greatly. It is known that well drained crushed stone ballast with a Tarvia finish will have a resistance from 2 ohms to 5 ohms per 1 ,000 feet of single track. On the other hand the resistance of roadbeds with solid concrete ballast in contact with the rails and also earth roadbeds, in which the ties are embedded and therefore in a more or less moist condition, are much lower and may be only from 0.5 to 1.5 ohms for 1,000 feet of single track. 3. Reinforcement of RaiL Conductivity. Early track construction practice in this country often included bare wire laid between the rails and connected to each bond. Sometimes one such wire was used for each rail, sometimes one for each track, and sometimes one served for a double track. The wires varied from No. 4 to No. 1, and were either of copper or galvanized iron. Their conductivity was small and they were subject to electrolytic corrosion and mechanical injury. This DESIGN, CONSTRUCTION, OPERATION, ETC. 33 construction has practically gone out of use. It is, however, common to find the rails in the vicinity of supply stations supple- mented by large conductors connected in parallel with the rails. This is not infrequently accomplished by the use of bare copper wire or cable buried between rails, and hence in full contact with the earth. Old rails, bolted and bonded together and buried beneath or beside the track, have also been used in some cases. Such buried conductors increase the leakage from the tracks and should be avoided. Supplementary conductors in parallel with the track and connected to it at frequent intervals tend greatly to insure the continuity of the return circuit, where the track bonds cannot be well maintained. Where copper cables are so used the occa- sional failure of bonds does not materially affect the track drop and their use may be justified where tracks are laid on filled or spongy ground or where the proper maintenance is unusually difficult. Buried bare conductors, however, increase the contact area between the return circuit and the earth, and the tendency to augment stray currents thus caused offsets to a greater or less extent the benefits attained by the reduction of drop. Copper installed in this manner is in parallel with the rails, and therefore has the same drop as exists in the rails. As track gradients rarely exceed two or three volts per thousand feet, this would mean that the drop on such cables would not exceed two or three volts per thousand feet, which corresponds to a current density of about 190 or 280 amperes respectively, per 1,000,000 circular mils. It will be seen that these densities are so low that such use of the copper is very uneconomical and for this reason this method of reinforcement of the rail conductivity should not ordinarily be used. Conductors are regarded as being in parallel with the rails when both ends are connected to the tracks or when one end is connected to the track and the other to a station busbar which is connected directly to the rail by a conductor of negligible resist- ance. The use of such conductors should not be confused with the insulated negative feeder system. 4. Power Supply. Among the various features of railway construction which tend to reduce stray current none has made more rapid advancement during recent years than the development of multiple feeding 34 DESIGN, CONSTRUCTION, OPERATION, ETC. points, principally from use of additional substations supplying the railway systems. Increasing the number of .substations will reduce the feeding distances and effect a saving in distribution copper and in line and return losses, and will also reduce the amount of current to be returned to any one point. The general effect is to reduce the track voltage drops, thereby reducing the amount of current which will stray from the rails to subsurface metallic structures. If The ordinary street railway system employs direct current ( at from 550 to 750 volts. Some interurban lines operate at 1200 volts direct current and voltages as high as 3000 volts are used on the electrified sections of some railroads. (a) High Voltage D. C. Railways. Railway systems of higher potentials than the ordinary 550-750 volt systems may cause more or may cause less stray currents than the latter, depending upon conditions. With the same -spacing of substations the current will be less in proportion as the voltage is greater. Usu- ally, however, advantage is taken of the higher potential to locate the power supply stations farther apart, maintaining approxi- mately the same current density in the tracks with the usual ft potential gradient. This, of course, results in increased overall jj voltage drops which tend to increase the stray currents. In making comparison of high voltage and low voltage systems from an electrolysis standpoint, the difference in conditions must be taken into account. As a rule high voltage direct current is used principally on roads having a private right-of-way with rails on ties supported on well drained rock ballast. Moreover, the major portion of such lines are located in country districts with no buried metallic structures paralleling them, but in some cases such lines pass through cities or towns, or at least enter their suburbs, in which event suitable measures to prevent injury by electrolysis should be taken. (b) Source of Stray Currents. A single trolley electric railway system with an adjacent buried pipe line is illustrated in Fig. 1, in which the underground network of pipes is represented by a pipe parallel to the tracks. At points remote from the power supply station, the current which reaches the rails from the cars will divide between the several possible paths, and the amount flowing along any path will be inversely proportional to the resistance of that path. A portion of the current, therefore, will leave the rails at points remote from the station and pass through the earth to the adjacent pipes, then flow along the pipes toward DESIGN, CONSTRUCTION, OPERATION, ETC. 35 K \ \ \ <0 i a- V) 36 DESIGN, CONSTRUCTION, OPERATION, ETC. the station, leaving the pipes near the station and returning through the earth to the rails and thence to the station as in- dicated by the arrows in Fig. 1 . The region near the station where the pipes are positive to the surrounding earth, and where the current leaves the pipes to return to the rails, is the region where damage by electrolysis will occur, and is called the danger or posi- tive area. ial Gradiev Dtsfance End of Line Potential Profile of Rai I vvay Ss tern Fig. 2. If the cars are uniformly distributed along the line, and if the track is of uniform resistance throughout its length, the voltage profile along the track will be as shown in Fig. 2. This curve is a parabola with a vertical axis and with its apex at the end of the line. The potential drop from the end of the line to any point on the line is therefore proportional to the square of the distance from the end of the line. The slope of this curve is a measure of the potential gradient. If the resistance of the track is^known, DESIGN, CONSTRUCTION, OPERATION, ETC. 37 the potential gradient at any point serves as a measure of the amount of current flowing in the rails at that point. If there are no metallic connections between the rails and the pipes, then the potential profile of the pipes will be something like that indicated in Fig. 3. In the regions remote from the supply station the pipes are ion Distance End of Line Potential Profile Showing Rails & Pipes Wrfhout Connections Between Pipes and Railway Return Circuit Fig. 3. seen to be negative to the rails and near* the station they are posi- tive to the rails. Ordinarily the positive area extends from 30 to 40 per cent of the distance from the supply station to the end of the line. At the neutral point where no potential difference exists between the pipes and the earth the stray current in the earth and underground structures is a maximum. The amount of stray current is more nearly a function of the 38 DESIGN, CONSTRUCTION, OPERATION, ETC. overall voltage drop than of the potential gradient at any point. While high potential gradients extending over a considerable length of track will result in a high overall voltage with corres- pondingly large stray currents, the existence of a high gradient on a comparatively short section of track is of much less con- sequence. The reduction of feeding distances and overall potentials has such a marked influence on stray currents that a rather full treatment of this subject is here given. (c). Relation of Feeding Distance to Stray Currents and Overall Voltages. The effects of the reduction of feeding distances on stray currents and overall potential drops are illustrated in Figs. 4 and 5. The stray current curves are calculated from the formulas found in Technologic Paper No. 63 of the Bureau of Standards, entitled "Leakage Currents from Electric Railways." They represent conditions on a typical line having the following characteristics: Double track, 72-lb. rails; length of line, 20,000 feet; calculated resistance of the track, 0.004 ohm per 1,000 feet (this figure allows for a 10 per cent increase in the resistance of 72 Ib. rails, due to the bonds; it corresponds approximately to the resistance of 2.5 million circular mils of copper). The leakage resistance is taken as 0.4 ohm for 1,000 feet, of double track which is a fair average for city tracks in paved streets with a crushed stone foundation. An average load of 40 amperes per 1,000 feet, corresponding to a headway of 4 minutes each way, is considered uniformly distributed along the line. The total average load is, therefore, 800 amperes, corresponding to a station capacity of 1,000 kw., on the assumption that the peak load is double the average load. Calculations of stray current have been made for both the insulated bus and the grounded bus conditions. This latter occurs only when all of the stray current returns to the negative bus without re-entering the track system, a condition which does not ordinarily occur in practice. An approach to a grounded bus would be a system where extensive pipe drainage existed with a large portion of the current returning to the bus from the under- ground piping and cable systems. Another condition which simulates a grounded bus is often found where bare copper cables which are used to connect the negative bus with the nearby rails are permitted to come in contact with wet earth or are laid in a stream or river bed. Railway stations generating direct current are often located in low ground or on rivers where condensing water is available and unless special precautions are taken to DESIGN, CONSTRUCTION, OPERATION, ETC. 39 insulate negative cables entering such stations they are likely to pickup considerable current from the earth, thereby establishing the condition of a semi-grounded bus. Fig. 4 shows the total current returning to a single supply station located at the end of the line. The stray current at any point is also shown for the cases of the bus grounded and the bus not grounded. By insulating the bus the maximum value of the stray 40 DESIGN, CONSTRUCTION, OPERATION, ETC. current is reduced from 417 amperes to 147 amperes and by putting the supply station at the middle of the line instead of at the end and thereby reducing the feeding distance to one-half, the maximum value of the stray current with insulated bus is reduced from 147 amperes to about 24 amperes. Fig. 5 shows the overall voltage curves for the same line fed from the end, from the center, and also from two stations located DESIGN, CONSTRUCTION, OPERATION, ETC. 41 at one-fourth and three-fourths of the distance to the end of the line respectively. Shortening the feeding distance to one-half reduces the overall voltage to one-fourth of the original value and cutting the feeding distance to one-fourth reduces the overall voltage to one-sixteenth of the original value; or as previously stated, the overall voltage varies as the square of the feeding distance. The curves in Fig. 5 are based on theoretical conditions with no stray current. The actual overall voltages would be somewhat less because of part of the current being in the earth. The dotted lines in Fig. 5 illustrate in a 'general way the 42 DESIGN, CONSTRUCTION, OPERATION, ETC. potential of the earth and pipes under the several conditions of feeding and the shaded portions represent the areas where the earth and pipes are positive to the rails The effect of providing additional centers of power supply can also be illustrated by the curves in Fig 6, which, while cal- culated on the assumption of no stray current, illustrate in a simple case, the effects which have been observed in practice. The curve SAO represents the track voltage drop on a portion of an electric railway system having a uniformly distributed load. The curve SBF illustrates the condition of a substation located at P, 33 per cent of the distance from Q to S, carrying 20 per cent of the total load. In this curve the portion BF is identical with AO. As the load is uniformly distributed, 33 per cent of the load is on the portion of the line shown by PQ, and of this 33 per cent, 20 per cent is carried by the substation P. The remainder, or 13 per cent, is carried by the station S. The point B on the curve SBF, therefore, corresponds to the point N on the curve SAO, the distance QR being 13 per cent of QS. In the same manner the curves SCG, SDH, and SEK are drawn showing the conditions when the station P carries 40 per cent, 60 per cent, and 80 per cent, respectively, of the total load. The summit of the curve SMD, in which the station P carries 60 per cent of the load, is located so that PL equals 60 per cent minus 33 per cent, or 27 per cent of the total length SQ to the left of P. The distance QL is, therefore, 60 per cent of the total length QS. In general, the conditions are more complicated than those here assumed, and will ordinarily prevent an accurate determina- tion of the relative potentials of the negative buses of the two stations. (d) Economic Considerations Invoked in Additional Supply Stations. The practical limit of feeding distances is one that cannot be determined by any general formula designed to fit all conditions. The economic aspects of the problem are far more complex than they appear at first glance and the proper solution involves a careful study of local conditions. However, an increase in the number of power supply stations may be said generally to reduce stray currents to a marked degree and with the advent of automatic control for railway substations the increase in the number of feeding points economically obtainable by this means should result in greatly improved electrolysis conditions. The number of substations for a given set of conditions may often be materially increased by some additional capital expendi- DESIGN, CONSTRUCTION, OPERATION, ETC. 43 ture, but with no increase in annual charges. Also, the original equipment may be distributed to additional stations with little or no capital expenditure, due to saving of feeder copper, and with no increase in annual charges. Number of Substations Relation of Number of 5ubsfa4ions -fo Annual Cnaraes -for Interurban Line Fig. 7. The curves in Fig. 7 show the results of calculations on a typical interurban railway system. They are based on the data con- tained in the paper by H. F. Parshall presented to the (British) 44 DESIGN, CONSTRUCTION, OPERATION, ETC. Institute of Civil Engineers, Volume 199; and on present day prices of copper and electrical machinery and labor. Ordinarily in laying out the number of substations for a given electric railway system, the minimum number consistent with economy will be the number selected, such as represented by the curve for manual operation at A. With the growth of traffic the number of stations in operation becomes increasingly inade- quate until a condition is reached represented by the point B on the curve, when additional substations are again added. In other words it is customary to operate along the curve from A to B with an insufficient number of substations. It appears, how- ever, that by operating between C and A on the curve instead of between A to B an increase of about 40 per cent in the number of substations can be made without effect on the total annual charges. It has been shown on page 40 of this report that when the overall voltage is divided by 4 the amount of stray current will be about one-sixth for the particular conditions discussed. An increase of 40 per cent in the number of substations will decrease the overall voltage to about one-half of the former value and there- fore reduce the stray current to about one-third. It appears, therefore, that by selecting the maximum number of substations consistent with economy instead of the minimum number, the railway companies could reduce to a large extent the stray currents without appreciably affecting their total annual charges and this method should be considered as one of the best possible solutions of the electrolysis problem. The curve for automatic substations is even flatter than that for manually operated stations, indicating that a very large increase in the number of automatic stations beyond the point of maximum economy may be employed without materially increasing the annual charge. It appears from these curves that if, while the electric railway companies are increasing their power supply, they will at the same time increase the number of power supply stations to the maximum economical number, then they can without any increase in the total annual charges eliminate the greater portion of the stray currents which cause electrolysis. In many situations the combination of railway substations with light and power substations may offer additional opportunities for economically providing points of supply without additional expense for buildings and attendance. (e) Automatic Substations. During recent years considerable progress has been made in the development of automatic, semi- DESIGN, CONSTRUCTION, OPERATION, ETC, 45 automatic, and remote control substations for electric railway service. Automatic stations were first used on interurban lines having infrequent service and the installation usually consisted of a 300 or 500 kw. machine. When a car or train of cars approaches one of these interurban substations the voltage of the trolley falls and when it has reached a certain point the substation auto- matically starts up and carries the load while the train is in its vicinity. As the car recedes from the substation the demand for current decreases and when the load has reached a predetermined minimum the substation shuts down. This type of substation with small converters has been success- fully introduced in some cities, the most notable installation being that at Des Moines, Iowa, where six substations were distributed throughout the city to replace one centrally located power supply station. The characteristics of large city loads are different from those on interurban lines. The movement of a single car produces but slight fall in the trolley potential and the starting and stopping of the substation is governed by the demand for power during the morning and evening rush hours. A few substations with large converters have been provided for such city service and are now in experimental operation. Remote control substations are also being developed for city service where they are required to operate continuously throughout the load period of the day or during the morning and evening peaks. Semi-automatic equipment, consisting of re-closing circuit breakers, time switches, and protective devices have been installed in a number of railway substations at a very much smaller cost than would be required for full automatic operation. The circuit breakers in the positive feeders automatically re-close after a definite time interval provided the short circuit or overload has been removed. The synchronous converter has to be started by hand and may be shut down either by a time switch or by hand. Otherwise it operates in a manner similar to those provided with full automatic control. The first cost of automatic substations is often justified by the saving in operating labor an_d feeder losses and the recovery of existing feeding copper. Minor savings arise from the elimination of light load losses and the station heating. A further benefit also to be derived from their general use is better voltage conditions and therefore faster car schedules. 46 DESIGN, CONSTRUCTION, OPERATION, ETC. The total amount of substation equipment now operated auto- matically is in excess of 50,000 kw., and much of the equipment being installed is intended for automatic operation or remote control. The increased savings attending this development will undoubtedly increase the number of substations which can economically be installed on both interurban and city systems, and if full advantage is taken of these economics, the feeding distances will be reduced to such an extent as to greatly reduce stray currents generally. ( f ) Location of Supply Stations. As pipes and other under- ground structures become increasingly positive to the earth as they approach street railway supply stations or the low potential points on the track system, it is obvious that if stations were located away from pipe networks trouble from electrolysis would seldom occur. As a rule other considerations will determine the location of supply stations in cities. However, on interurban lines the protection of piping systems in small towns against electrolytic corrosion often presents a grave problem because of the long feeding distances and the difficulty of employing the measures of mitigation ordinarily used in city systems. Under such conditions the location of the supply station at a distance from the city and away from the underground structures may be the most satisfactory way of insuring their protection. This is particularly true of automatic substations which require no regular attendants. The character of the earth in the vicinity of supply stations naturally has an important effect on the magnitude of stray currents. It is, therefore, desirable to avoid connecting negative feeders to tracks in unusually wet locations. (g) Alternating Current Systems. When the first alternating current railways were proposed, the question of possible electrolytic effects received special investigation. Considerable work was done upon a laboratory scale, in which it was established that alternating currents could produce corrosion on electrodes of the metals commonly used underground, such as lead and iron, but that the effects were very much less in magnitude than those produced by equivalent direct currents, usually less than one per cent and in most cases negligible. See Fig. 16. The objections to the substitution of alternating current for direct current in the case of systems already installed in large cities are so well known and so serious that the question needs no discussion. DESIGN, CONSTRUCTION, OPERATION, ETC. 47 5. Interconnection of Tracks. Electrical interconnection between parallel tracks in close proximity, or of tracks, one of which passes over the other, be- longing to the same or different railway systems is usually a necessity in order to prevent wide fluctuations of voltage between the tracks. Such interconnections tend to equalize the potentials of the tracks so connected and thus tend to prevent the flow of current from the track of high potential through earth and inter- vening metallic subsurface structures to the track of low potential. In general such interconnections also afford a saving in track losses. Whether parallel tracks should be connected naturally depends upon the distance between tracks, location of supply stations, leakage characteristics of the roadbeds and other local con- siderations. Interconnection generally reduces the track voltage drop by providing more metallic paths for the current. It has also the same general effect as cross-bonding between rails of the same tracks, in that if one track circuit should be accidentally opened the current would be shunted around through the interconnection to the other track. As a rule interconnection of tracks will improve electrolysis conditions but may be detrimental to one locality while improving conditions in another. A failure of one of the companies to maintain its bonding would naturally tend to increase the current on the better bonded track. Interconnection of tracks has been found to be particularly advantageous where two or more lines of electric railways operating in one locality and belonging to the same or to different systems are supplied from two or more power stations located in different parts of the city. By interconnecting the tracks of such lines in the neighborhood of the power stations and also at several inter- mediate points a reduction in the resistance of the return circuit can be brought about whereby the drop formerly existing in one track can be balanced by the drop in the opposite direction in the other track. The rail drop in each track is greatly reduced and all high potential gradients between tracks eliminated. Where the tracks of the two independent railway systems are parallel and a short distance apart, and fed by power supply stations in opposite directions the potential profiles of the rails will be as shown in Fig. 8 in which, for simplicity, the negative buses at the two stations have been assumed to be at the same potential. In the figure are also indicated the potential profiles of the pipes adjacent and parallel to the two sets of tracks. 48 DESIGN, CONSTRUCTION, OPERATION, ETC. If then gas or water pipes extending from the parallel mains cross under two sets of tracks at different locations where the tracks are at a considerable difference of potential, as at RB, Fig. 8, then the pipes may be negative to one track and positive to the Station A Station B Potential Profile oftwo Independent Railway Systems Sho wincr Effect of Interconnection Fig. 8. other. At the crossings where the pipes are positive to the tracks electrolysis will be liable to occur. If now the rails of the two systems are interconnected at points near the two stations and also at intermediate points the potential profile along the rails after such interconnection will be as shown by the curve OYP. It will be noted that this interconnection DESIGN, CONSTRUCTION, OPERATION, ETC. 49 results in a very considerable reduction of the potential drop in the return circuit, and the resulting reduction in the losses will in many cases be alone sufficient to warrant the cost of the inter- connections. Railway systems employing track circuit signals must insulate their rails used for signal circuits from other systems in order that other currents may not be introduced in the signal circuits and for this reason cannot avail themselves of the advantages of inter- connection. This applies only to rails used for signal circuits. B. FEATURES OF RAILWAY CONSTRUCTION AND OPERATION EMPLOYED FOR ELECTROLYSIS MITIGATION 1. Insulated Negative Feeder System. Of the various methods of railway construction and operation employed to improve electrolysis conditions, the insulated nega- tive feeder system has been most widely used. While it has been generally thought that such a system is necessary in connection with a large supply station if underground structures are to re- ceive adequate protection, the present tendency to greatly increase the number of railway supply stations, and particularly the development of the automatic substation makes the extensive use of insulated negative feeders less important. An increase in the number of track drainage points is often more economically attained by the use of more substations than by the use of insulated negative feeders. The tendency is now in the direction of a relatively few short insulated negative feeders and a large num- ber of substations, rather than an extensive use of insulated feeders from a few large supply stations. (a) Description. In the insulated negative feeder system, instead of tying the tracks directly to the negative bus and de- pending on the tracks and such copper conductors as may be in parallel with them to return the current to the supply station, the connection at the station is either removed or a suitable resistance is inserted and insulated feeders are run from the bus to various points on the track. By thus taking the current from the rails at numerous points, high current densities, and consequently high gradients and overall voltages, can be avoided to any desired degree. As the feeders are entirely insulated from the earth except at points of connection to the tracks, the actual drop in potential in the different feeders is of no importance so far as electrolysis is concerned, so long as the drop is approximately 50 DESIGN, CONSTRUCTION, OPERATION, HTC. DESIGN, CONSTRUCTION, OPERATION, ETC. 51 the same in all feeders. It is possible, therefore, to impose any limiting value of overall-track drops and track potential gradients on the track and still be free to design the feeders to give maximum economy which is not possible when the feeders are connected in parallel with the track. Insulated feeders are sometimes designed for equal potential drops, in which case the several points of connection to the tracks are at the same potential and the system is called an equi-potential or balanced system. When the shorter feeders are designed for a lower drop than the longer feeders, the system is called a graded potential system. Fig. 9 shows the overall voltage curves representing conditions on a track which is connected directly to the negative bus and with which no additional feeders are employed. The curves are parabolas with the same constants as those in Figs. 2 and 5. Fig. 10 illustrates the same system with insulated negative feeders extended to four points on the track, two in each direction, with a resistor connected to the nearest point on the track. The feeders and resistance are so proportioned that the drop on all is the same under average load conditions and they, therefore, form an equi-potential system. The curved lines represent the poten- tial of the track from point to point, and, as in Fig. 9, the curves are arcs of parabolas. An equi-potential system of this kind, while it reduces potential differences on the tracks to a minimum and therefore affords the maximum reduction of stray current, usually involves increased energy losses in the return circuit as the rails are merely used as distributing mains for the feeders and are not taken advantage of to return current to the supply station. The equi-potential principle is better adapted to a city network than to a single line, as feeders can be extended to several points on the network at approximately the same distance from the station, and these points can thus be maintained at the same potential. As a rule, however, a gradient is permitted between the points so selected and the track at its nearest approach to the supply station. An arrangement approaching an equi-potential system is shown in Fig. 1 1 , where four feeders are connected to the track at important intersections and connection made to the track near the station through a resistance. One of the feeders is shown connected to^ the track at two points, a resistance being inserted at the point nearest the station. This system and also the one illustrated in Fig. 10 are practically 52 DESIGN, CONSTRUCTION, OPERATION, ETC. DESIGN, CONSTRUCTION, OPERATION, ETC. 53 equivalent, in the reduction of stray currents, to independent substations at the several points where the current is removed from the track; that is, the results, so far as voltage drop on the tracks is concerned, is the same whether a number of stations or an equal number of insulated negative feeders be employed, but the energy losses in both the positive and negative conductors are very much greater with the negative feeder system than with the same number of substations. Fig. 12 illustrates an insulated negative feeder system so de- signed that the direction of the current in the rails is not reversed as in the equi-potential system. This graded potential system results in a slightly higher potential at the terminal of each suc- ceeding feeder, starting from the station, and these higher poten- tials on the longer feeders result in higher overall track potentials than with the equi-potential system, but allow a material saving in copper in the negative conductors. In designing graded potential feeder systems, it is customary to limit the gradients on the tracks to some definite amount, such, for example, as an average value of 0.5 volt per 1000 feet and to remove all of the current from the track over an insulated feeder wherever this limiting gradient is reached. By removing no more current at any point than has accumulated up to that point, the current in the track is nowhere reversed and a continuous gradient toward the station is maintained as illustrated in Fig. 12. (b) Application of Insulated Negative Feeders. No definite rules can be laid down regarding when and to what extent insu- lated negative feeders should be used. In city networks the negative bus should generally be connected to the track at more than one point, that is, negative feeders should be extended along the tracks to nearby intersections. Small stations of 300 to 500 k.w. capacity in city networks may usually be connected directly to the track at one point only and preferably to the nearest track intersection. Insulated negative feeders should be run from the negative bus to the rails in such a manner as to insulate them thoroughly from the earth and from each other. The tying together of any of these feeders should be avoided. In some cases, however, it may be allowable to tie a single feeder to the rail at two or more points through resistances to adjust the currents drawn from the tracks at the various points of connection. Connections to tracks in wet locations make possible excessive 54 DESIGN, CONSTRUCTION, OPERATION, ETC. I Q> "0 o I DESIGN, CONSTRUCTION, OPERATION, ETC. 55 current^discharge from adjacent underground structures and should therefore be avoided where possible. Means should be provided on all negative feeders and feeder taps for conveniently measuring the current flow thereon, and where practicable these means should be installed within the railway power station. Application to Interurban Lines. In the case of a single line, little is to be gained by the use of insulated negative feeders unless they are run considerable distances from the power supply station. For this reason they are not as well adapted to reducing stray currents from interurban lines as from city networks as the follow- ing explanation will show. It has been shown in the section on Power Supply that stray current results from the action of large overall voltages rather than from high potential gradients. Large overall voltages may be produced either by concentrated city loads over relatively short feeding distances or by comparatively light loads on long lines. The former condition can often be effectively dealt with by the use of insulated feeders because of the short distances in- volved and a traffic of sufficient density to justify such an ex- penditure. A very different condition exists on interurban lines where a corresponding reduction in overall voltages would require very long insulated feeders entailing large expenditures for copper and large power losses. The effect of installing insulated negative feeders within the limits of a small town through which an interurban lines passes is illustrated in Fig. 13. Without the use of negative feeders, that part of the piping system within the city limits is shown to be positive to the tracks, a condition which is often found in practice, although not a reliable criterion as to the degree of hazard to underground structures as pipes are sometimes positive to the rails and negative to the adjacent earth. If the potential gradients on the tracks within the city are reduced or eliminated by the use of insulated feeders, the overall voltages are only slightly affected and the potential difference between the pipes and tracks not greatly reduced. In some instances where insulated feeders have been applied on interurban lines, the positive area has actually been extended and no material improvement in the general condition effected. It is not the intention here to condemn entirely the use of insu- lated^negative feeders for interurban electric lines, because in some cases they have been successfully used. Local conditions 56 DESIGN, CONSTRUCTION, OPERATION, ETC. DESIGN, CONSTRUCTION, OPERATION, ETC. 57 vary widely and each problem should, therefore, be worked out on its own merits. However, it can safely be said that this method of electrolysis mitigation is not so well adapted to interurban lines as to city systems. (c) Negative Boosters. Negative boosters are sometimes used in connection with the insulated negative feeder system abroad, but not in this country, so far as known. Unusually long feeders which would have to be very heavy in order to keep the voltage drop comparable with that on the other feeders can be reduced to the minimum size that will carry the current if provided with a booster. When so used, the booster permits a saving in copper but involves an additional energy loss on the conductor. Boosters can also be used to equalize the voltage drops on feeders of differ- ent lengths. They have proved economical under certain condi- tions and uneconomical under others. In general it is simply a question of the fixed charges on copper as against the fixed charges and operating cost of machines. 2. Three-Wire System. (a) Description. This method of power distribution is similar to that commonly used for city light and power, and known as the Edison three- wire system. It may take two different forms which are the same in principle, but which differ radically in the arrange- ment of the feeder system. One of these, known as the parallel three- wire system, is directly analogous to the ordinary three-wire power and lighting system. The typical arrangement for the case of a double-track line using this system is shown in Fig. 14. Here one trolley is negative and the other positive, the tracks being the neutral conductor. This results in a potential difference be- tween trolley wires equal to twice the operating voltage at points of connection between the trolley sections. It is evident that only the difference in the load on the two sides of the line returns to the powerhouse on the track, although there may at times be heavy circulating currents flowing between cars in short sections of track. If the cars run at frequent intervals, however, such cir- culating currents will not have to flow over sufficiently great dis- tances in the tracks to cause nearly as large track drops as would occur with the same loads under two-wire operation. The result would be that where load conditions are reasonably favorable for the three- wire system, large reductions in potential drops in the negative return could be secured. While almost perfect electrolysis conditions could be obtained 58 DESIGN, CONSTRUCTION, OPERATION, ETC. o $ D . Neu-traK ] s~* <-, > i y 1 Positive Feeder^ jystem ^ Positive Feeder ^_ -4 > rOi | Negative Feeder/ Sectionali-Ered Three Wire System Fig. 15. Parallel Three Wire S Fig. 14 r- f I Trolley Wire^ | ] ? j j 2 K ? * Tracks DESIGN, CONSTRUCTION, OPERATION, ETC. 59 with the parallel three-wire system, the difficulty of properly in- sulating the two trolley wires from each other, especially at cross- ings and switches, has been considered so great that the sectional- ized three-wire system is considered the more practicable and has therefore been employed in all installations which have come to our attention. It is shown diagrammatically in Fig. 15. In this form the feeding district is divided into sections, and alternate sections are supplied by feeders running from the positive bus, while the remaining sections are supplied by feeders from the negative bus, the difference of potential between the two buses being approximately 1,200 volts. In this way, the existence on the same portion of the street of two trolleys having a high difference of potential between them is avoided. The tracks, as before, serve as the neutral conductor and convey the current from the cars in one section to those in the adjoining section and return the unbalanced current to the powerhouse. (b) Insulation of Trolley Sections. The problem of insulating the positive and negative trolley sections from each other is one that will require considerable care. At points of simple junc- ture this has been accomplished in some cities by the use of two standard 600-volt trolley section insulators in series, with a dead section of trolley wire from 4 to 6 feet in length between them. In other cities the two section insulators are brought to- gether, thereby simplifying the overhead construction. It is also possible to use a single 1,200- volt section insulator 18 to 24 inches long. Where trolley wires of opposite polarity cross, it will probably be found better to make the entire intersection of one polarity rather than try to insulate the crossings. At the inter- section of two double-track lines this will mean the installation of four double section insulators as just described. Where such changes are made, the more important of the two lines should be made the continuous one to avoid interruption of service due to failure of power on the other line. Warning signs should be hung on the span wire at all section insulators and motormen should be instructed to coast across these points. (c) Costs. The principal economy resulting from the installa- tion of the three-wire system, is the saving in track losses, which are greatly reduced, although not entirely eliminated, while there usually will be increased station losses due to the necessity of always operating two sets of generators or converters. In systems having a relatively small number of multiple unit, power supply stations, the cost of converting a system for three- 60 DESIGN, CONSTRUCTION, OPERATION, ETC. wire operation is usually, but not always, smaller than the first cost of insulated negative feeders, or any other measure that will give the same degree of protection from electrolysis. The avail- able data on three-wire systems, both as to costs and effects of electrolysis conditions are not sufficient to warrant the laying down of general rules as to the extent of its application. The local factors involved in each case are often peculiar and require special consideration. In cities where uninsulated negative copper has been installed, it may be reclaimed after conversion to three- wire operation, unless it has been installed under pavement or embedded in con- crete, and the salvaged copper may largely, if not entirely, cover the cost of conversion. It is good practice to provide an additional bus in the supply station for the generators and feeders operated with reverse polarity. Double throw switches are also installed for these feeders and generators. (d) Difficulties and Limitations. One difficulty which some- times will be encountered in three-wire operation is that of re- duced station capacity, as two or more machines operating in parallel will have a much greater capacity at times of excessive demand than when divided on two independent circuits. Heavy interurban trains, particularly when starting, often demand the full capacity of a supply station and the same condition exists at times of unusual loads, such as occur after a tie-up or following a ball game or circus. Where the generating capacity of both the positive and negative sides of the system is large in comparison to the maximum demand of any trolley section, this objection does does not exist, but where only a single small machine is available for one side of the load, considerable difficulty may be encountered in taking care of the peak demands under extreme conditions. Where necessary these extreme peak demands can be taken care of by operating all of the machines on one polarity during this period. Double throw switches, by which this can quickly and conveniently be accomplished, are usually provided with three- wire operation. One instance of an overload with three-wire operation resulted in the too frequent blowing of the circuit breaker on the negative generator. This was eventually overcome by installing a series resistance which is automatically cut into the circuit when the current reaches a predetermined maximum value, thereby limiting the current to a fixed amount. The equipment used for this pur- DESIGN, CONSTRUCTION, OPERATION, ETC. 61 pose is identical with that employed for. automatic railway sub- station control. Not only are unusual loads of short duration difficult to take care of with three- wire operation, but where the entire capacity of a station with all machines in parallel is required to carry the normal peak-load, it may be impractical to convert for three- wire operation. In general, it will, of course, be difficult to divide the positive and negative loads in the same ratio as the capacities of the two groups of generators assigned to them. Moreover, the load factor of the whole system is always greater than that of any part, and the generators when divided into groups will therefore be operating at poorer load factors and con- sequently at lower efficiencies than. when in parallel. Therefore, where no excess generator capacity exists, it may sometimes be necessary to install an additional unit in converting a system for three- wire operation. Owing to the continual movement of cars from one trolley section to another of opposite polarity, there is a considerable variation in the track potential at any point. This is particularly true on lightly loaded lines and results in wide fluctuations, and even reversals, between the tracks and adjacent underground structures. While the algebraic average values of such potential differences may be greatly reduced by the adoption of a three-wire system, a continuously negative condition of underground struc- tures cannot ordinarily be expected. Other difficulties of less importance have been suggested: (1) Some equipment, such for example as arc-headlights, ampere- hour-meters and auxiliary battery control, requires a single polarity for its successful operation. Where such equipment is used it will be necessary to provide reversing switches. (2) Two trolley poles in parallel cannot be employed on a single car or on trains as they would bridge trolley sections of opposite polarity when moving across section breakers. (3) A negative trolley would change the character of the electric arc used on tracks for arc- welding and building up joints and in some operations might be objectionable. (4) Commercial customers receiving power from trolley feeders may, in some cases, be inconvenienced by a change of polarity. (e) Practicability. None of the difficulties here cited can be considered of insurmountable character, and like many other things, the system can be made to work satisfactorily if the neces- sary attention is given to it. Experience has fully demonstrated 62 DESIGN, CONSTRUCTION, OPERATION, ETC. that it will greatly improve electrolysis conditions when properly applied and also give better operating voltage at the cars. How- ever, to secure the best possible results with this system, it will often be necessary to change feeder copper and shift section in- sulators to obtain the desired sectionalization . (f) Extent oj Adoption, Until recent years the three-wire system has not been employed for street railway work in this country, although it has been in use in Brisbane, Australia, and Nuremberg, Germany, for a number of years. In the last few years it has received some attention in America and is now in operation in Omaha, Wilmington, Winnipeg, Canada, and in some portions of Los Angeles and Milwaukee. The Los Angeles installation has been in operation since 1915 and more recently has been extended to include several additional station districts. In Omaha a trial installation in one station district was made early in 1917. After several months' trial with the experimental installation, the main station district was con- verted for three-wire operation and has since been so operated. Three-wire operation was adopted in Winnipeg as a means of meeting the requirements of a law passed by the Manitoba Legis- lature, prescribing certain limitations in track voltage drops. Two substation districts were changed over in 1919, and since that time practically the entire system has been converted to three-wire operation. In 1920, after considerable experimenting, a three-wire system was substantially completed in Wilmington, Delaware, and a complete electrolysis survey made under both two-wire and three- wire operation. With the latter, a considerable improvement in car operation due to higher average voltage was reported, and also better electrolysis conditions on water and gas pipes. Stray currents and overall potentials were reduced to about one-half their values with two- wire operation. Reversing potentials were found on the telephone cables in some areas and some adjustment of the drainage of this system will be necessary before it can be said to be entirely satisfactory. 3. Reversed Polarity Trolley System. This method of railway operation involves using the running tracks as the positive conductor instead of the trolley wire. It has at various times been suggested as a means of electrolysis mitigation, and in at least one case it has received an extended trial.. Fundamentally, however, it is not a mitigation method, DESIGN, CONSTRUCTION, OPERATION, HTC. 63 because it merely reverses the direction of the stray current and in no way affects the magnitude thereof. With reversed polarity the same amount of corrosion will result as with normal operation and the only difference will be the localities in which the damage will occur. Under normal operation using the running tracks as the negative conductor, the electrolytic damage will generally be con- fined to the area immediately surrounding the direct current power station or the track feeder connection points. With reversed po- larity, the electrolytic corrosion will be scattered over the out- lying districts which with normal polarity would constitute a negative area. If the trolley system is operated with reversed polarity, it is extremely difficult to effectively drain the lead sheaths of underground cable systems, because there is no definite point of low potential to which to drain. In 1912 the polarity of the electric street railway system in New Haven, Connecticut, was reversed making the running tracks the positive conductor. This method of operation was adopted by the railway company in order to afford immediate relief to the gas works, and to the water and gas piping systems in the central part of New Haven, where very serious damage was occurring. It was then thought that in the outlying sections the damage would be less concentrated, and also failures would be less serious and more easily repaired, than in the central business district. It soon became evident that it was practically impossible to adequately drain the underground telephone cable system, and that even with reversed polarity the general electrolysis conditions of the water and gas piping systems were still far from satisfactory, and after a trial of eight years, this method of operation was abandoned. The New Haven experiment therefore, indicates that the reversal of railway polarity to rails positive is merely a means of relieving dangerous electrolysis conditions in the vicinity of the power station, at the expense of the cable and piping systems at some distance from the station. When no underground cable systotns are involved, reversed polarity is useful as a temporary means of immediate relief to an endangered piping system in the interval immediately preceding the installation of effective electrolysis mitigation. 4. Periodic Reversal of Trolley Polarity. If the polarity of the trolley is reversed daily, at a time when the load on the system is a minimum, few operating difficulties will be encountered and some improvements in electrolysis condi- 64 DESIGN, CONSTRUCTION, OPERATION, ETC. tions will result. It is obvious that pipes in any locality will be in a positive condition only half as long as with normal operation, and there may also be a further reduction of electrolysis due to redeposition of the corroded metal during the period when the t" V /n Co efficient of Corrosion at Different Frequencies of Iron Electrodes in Soil. ^- s s / a eo *so / 40 7 U 30 y / * / "t 20 ^ x^ ^ !o . -* . * ^^ J* s *: + 2 0) o o5 Sfl^ :!- 2 ^i ^li if I' it II ti. x > IlKfi- s!l?:D2 -oonr- g U oS - aj . v, 31 6x ** l^ 1 'O*G'-* OO'-'JrJ'CO '- ioooC'r'aj'Oo -NTjeooot*a>oio * * S 2 & S S s Js 3 g * 78 DESIGN, CONSTRUCTION, OPERATION, ETC. mall fraction of the original value. The change was attributed to the slow oxidation of the sulphur contained in the compound, resulting in the production of sulphuric acid. No corresponding data are yet available on "Metallium." (d) Dresser Couplings of the ordinary type which have been extensively used on wrought iron and steel gas mains are uncertain and variable in their resistance, depending upon the manner in which they are installed. However, if used throughout any pipe line their average resistance is so high as to practically eliminate the flow of stray current. (e) Special Insulating Joints. A special high resistance joint is made, known as the "Dresser Insulating Coupling," and is used to prevent the flow of stray current on pipes. Insulating joints, such as wood stave joints, and flange joints with insulated bolts and gaskets of insulating material are sometimes used on large mains at river crossings or at points of intersection with street railways and at other special locations. The effective length of such joints can be increased by thoroughly insulating the pipe with wrappings or covering for some distance on either side of the joint. This treatment is often applied to important oil and high pressure gas pipe lines. (f) Insulating Joints Applied to Kxisting Pipe Lines. Pipe lines acting as ties between two extensive systems or networks sometimes carry considerable current from one system to the other and this can be reduced or practically eliminated by the use of comparatively few insulating joints installed in the main con- necting the two systems. To distribute the stray current around insulating joints so installed, the joint can either be made long or the pipe insulated for some distance on either side. A large industrial plant or a small community may be supplied with gas or water through a single pipe over which stray current may flow and cause damage at some point which would otherwise not be in danger. The use of one or more insulating joints will often correct such a condition at little expense. A pipe line crossing under an electric railway track or through a river or wet ground can be prevented from discharging or collecting current at such points by the use of insulating joints on both sides of the exposure. Service pipes which are subject to corrosion at points where they cross under railway tracks are often insulated from the mains by the use of insulating joints at times of replacements thus pre- DESIGN, CONSTRUCTION, OPERATION, ETC. 79 venting the further passage of current from the main to the service. Insulating joints are also frequently used to prevent the inter- change of current between two piping systems, as shown in Fig. 18, or between a piping system and a cable system or other under- ground structures. In order to protect gas services or water services where they cross under tracks, it is often necessary to install insulating joints both at the main and within the premises to prevent the flow of current from services of another system to which they may connect. This condition exists where gas water heaters are in use as these appliances usually make a firm metallic contact between the gas and water services. In Fig. 20, if the gas and water mains are both positive to the track, accelerated corrosion will take place on the services where they cross under the track. To protect one service without regard to the other, it is obviously necessary to install insulating joints at A and B, or C and D. Insulating joints have been installed at selected locations by some gas and water companies as an auxiliary to a negative feeder system. For example in Providence, Rhode Island, after an insulated negative feeder system was put in operation insulating joints were installed on gas and water mains to still further reduce the stray current on the pipes. The cost of installing insulating joints when pipes are uncovered for repair or replacement is comparatively a small item, and often affords a satisfactory means of preventing further damage to them. 3. Shielding. In special cases underground structures have been protected from electrolysis by connecting to the structure an auxiliary metallic conductor located so as to cause the current to flow to earth from the auxiliary conductor. This mode of protection is known as shielding. The method has in some cases been applied to the dead end of an underground metallic structure which is highly positive to earth. In such cases an auxiliary shielding plate or pipe of adequate ground contact surface extending beyond the dead end and electrically connected to the structure to be protected has been installed in such a manner that the bulk of the current was caused to leave the auxiliary shielding conductor, thus affording a certain degree of protection to the dead end of the structure. One application of this method, which is in use, is 80 DESIGN, CONSTRUCTION, OPERATION, ETC. * I 1 I * i c 1 -2 2 (0 ,S _c >N^ T <3 i 5 8 "5 "*" = 5 S ( 1 i - LJ 0) V cfr- mm "2 . ^ x * ^ i, c I MMHM i ? CO fc to T r g * 1 ( t c (U O co v ~f II u Q \ 'x / \ (^ "T* * * Ifcl 1 . - ^$ ^J (1) W ^ 5- - E ( \ ( t 3 I I 8 ^ W:| 1 ( i I i aJ .? CO i. "If K 4- C ?r?^ i 12 DESIGN, CONSTRUCTION, OPERATION, ETC. 81 that of a service pipe crossing under tracks or crossing other structures to which it is positive and where the pipe comes rela- tively close to the rails or other structures at the point of crossing. In these cases a larger shielding pipe, usually of heavy cast iron, has been placed around the service pipe and electrically connected to the service pipe and extended sufficiently on each side of the crossing so that the major part of the current was caused to leave the shielding pipe, thereby corroding the latter while protecting the service pipe. It is very important that a thorough metallic connection be made between the pipe to be protected and the shielding pipe. Otherwise, the service pipe is likely to corrode where current leaves it to flow through earth to the shielding pipe. Unless the shield is in the form of a pipe completely surrounding the structure to be protected, this method of protection is uncertain and should be used only in very special cases. When applying this method it has been found necessary to take care that the auxiliary shielding conductor does not merely increase the electrode area from which the current leaves, because in this case the current will continue to leave from the structure which is to be protected unless an insulating covering is applied to the pipe beyond the protecting shield. This has been found to be the practical result where a shielding conductor of the same or less contact area was placed in the earth near the structure to be protected and where the stray current has left both structures. III. MEASURES INVOLVING INTER-CONNEC- TION OF AFFECTED STRUCTURES AND RAILWAY RETURN CIRCUIT A. ELECTRICAL DRAINAGE OF CABLE AND PIPE SYSTEMS Electrical drainage consists in connecting the affected structure to the railway return circuit by insulated conductors in such a manner that the current leaves the structure through these connections instead of flowing to earth. This prevents corrosion in the neighborhood of the drainage connections, but increases the current flowing on the structure and the voltage drop along it, which latter results are generally undesirable for reasons discussed in detail in subsequent paragraphs. Drainage connections are usually made by running copper cables either to the busbar of the railway supply station or to negative return feeders. Connections to tracks should be avoided 82 DESIGN, CONSTRUCTION, OPERATION, ETC. because the failure of rail bonds might cause dangerous currents to flow over the drainage connection and also because of the pos- sibility of getting a current reversal, particularly when the adjacent substation shuts down during the light load period. However, when insulated negative feeders are used, the drainage connections may be made to the rail terminals of the feeders. Connections to rails are sometimes installed where a conduit line or a pipe crosses a railway track at a considerable distance from the power supply station and other means of draining would be awkward and expensive, but they should be made with considerable dis- cretion and should be carefully recorded and regularly inspected. Where used, drainage should be reduced to a minimum con- sistent with the protection of the drained structure in order to reduce the hazard to other adjacent underground systems. The drainage of one system tends to establish differences of potential between the various underground systems, resulting in interchange of current with consequent injury to the system at the higher potential. In order to avoid this condition, it is de- sirable to interconnect the various systems and drain them over common conductors. As structures owned by different interests cannot be bonded together except by an agreement between the owners this has frequently of itself made it impossible to apply a comprehensive drainage system to all structures because of the impossibility of obtaining an agreement of all owners to allow connections to their structures, except on condition that other interests assume liability for any injury which may result from such interconnections. If, however, the foregoing method of unified drainage is carried out so that the drained structures are at all times negative to earth, no electrolytic corrosion of such structures will result. Just how difficult it may be to maintain pipes negative to earth at all points and at all times by means of drainage is a question which cannot be answered until investigations have been carried further. The objections to electrical drainage apply most forcibly to pipe networks, particularly to gas and oil pipes on account of the inflammable substances carried. Drainage should be considered only as a supplementary measure to the improvement of the rail- way return circuit or as a temporary measure in cases where acute electrolytic corrosion has resulted. It can never take the place of an adequate railway return circuit. Notwithstanding its numerous disadvantages and limitations, DESIGN, CONSTRUCTION, OPERATION, ETC. 83 there are engineers who believe that pipe drainage has a definite field of usefulness. The Committee, through its Research Sub- Committee, is still actively engaged in investigating the magni- tude and importance of the technical factors involved and until further information shall have been acquired, the Committee will not be in a position to reach a conclusion on this subject. 1. Drainage of Cable Sheaths. (a) Method of Draining Cable Sheaths. In order to afford com- plete protection to cable systems, it has been found that they should be interconnected and have drainage conductors of sufficient conductivity located so that the lead sheath of the cable network is everywhere lower in potential than the adjacent earth. Cable systems are usually installed in vitrified clay, creosoted wood, or fibre ducts, and if kept free from water, the tendency to collect current is much less than if they were in direct contact with the earth. Owing to the higher resistance thus introduced between cables and earth and the continuous character of the cable sheaths, it is usually possible to lower the potential of the system below that of the adjacent earth in all localities by draining relatively small currents at one or more points. In order to prevent the interchange of current through earth between the several cable sheaths in any conduit system, it is necessary to bond the sheaths together at frequent intervals. Some companies make a practice of bonding at every manhole and good practice requires such bonding at intervals not to exceed five hundred feet. Bonding is usually accomplished by sweating a flat copper strip or a copper cable to all cables within any system which may properly be bonded together. Foreign cables which enter any duct system are also bonded to the system they parallel. It is often necessary to interconnect signal cables with lighting and power cables so as to avoid differences of potential which might otherwise occur, but where this is done, a fuse should be installed in the bond connection to the signal cable so as to eliminate the possibility of high voltage current getting on the signal cable sheaths. It is desirable to provide means for measuring all drainage currents and where the drainage feeder is extended to the supply station, an ammeter or shunt is usually installed for that purpose within the station. Where the drainage cable does not enter the supply station, measurement can be made within a manhole or on a pole, or wherever the drainage cable is accessible. Where a cable system tends to become positive in regions remote 84 DESIGN, CONSTRUCTION, OPERATION, ETC. from the railway supply station, it is necessary either to use a long copper cable for drainage at a considerable expense or to resort to some other method of protection. Aerial telephone cables are sometimes used for this purpose, but are not employed except when other conductors are not available or would be unduly expensive. Cables are sometimes found to be positive only during certain periods of the day or their potential may reverse from time to time due to fluctuations in the railway load. Where this condition is considered dangerous from the electrolysis standpoint an automatic switch is sometimes installed which is closed during the period the cable is positive and automatically opens when the cable becomes negative, the object being to prevent the cable from taking on current while in a negative condition. The cost of automatic switches and the fact that they add an objectionable complication to the plant are reasons why their use should be restricted as much as possible. Automatic or manually operated switches should be provided in all drainage cables terminating in railway supply stations in order that they may be opened during the period when the station is not in operation. Automatic substations which start and stop without attendants should be provided with facilities for accom- plishing this result. (b) Heating Effect of Stray Current on Cable Sheaths. Stray current on the sheaths of lead covered cables causes a heating effect which impairs the carrying capacity of power cables. In some cases this effect may be objectionable. The following formulae have been developed for single conduc- tor and three conductor cables to give their current carrying capacity when sheath currents flow. The values obtained give the conductor the same temperature rise above surrounding structures as produced by their normal current when no sheath currents are present. The formulae have been developed on the following basis: 1. That the watts dissipated in the sheath are effective in raising the sheath temperature but that they do not affect the rise of the conductor over the sheath. 2. Resistivity of lead 12 times that of copper. This assump- tion, while not strictly correct, will give results within an accuracy obtained by considering other factors as constants, such as the radiation constants of the lead sheath. DESIGN, CONSTRUCTION, OPERATION, ETC. 85 Definitions A = temperature rise of conductor over sheath for a given con- ductor current. B = temperature rise of sheath over cable surroundings for the same conductor current as for A . C = temperature rise of conductor over cable surroundings for the same conductor current as for A and B. D outer diameter of lead sheath in inches. d = inner diameter of lead sheath in inches. r ! . , area in circular mils a = area or conductor in circular inches = l,UUU,Uu(J I s = amperes flowing in sheath. 7 = normal current rating of cable. X = defined as I'o I = conductor current with (XI ) sheath currents. For Single Conductor Cable 12a For Three Conductor Cables /= T _,, 4aX 2 B (D*-d*) (A + B) The values of A, B, and C can be found for single and three conductor cables by referring to Atkinson's article on "Carrying Capacity of Cables" in the September, 1920, issue of the Journal of the A. I. E. E. Examples 1. Single conductor cable, 250,000 C. M., 1/8 inch lead sheath, 4/32 inch paper insulation. Normal current 510 amperes. What is resultant carrying capacity with 100 amperes sheath current? = = . 196, X* = . 0384. a = .250, = = .735. olU L> Zo .U D = 1 .09, d = .84, D 2 - d? = .484. Resultant carrying capacity=510yi- !!LMLL^ 510 (.91) = 463 amperes. 2. Round Three Conductor No. 4/0, paper insulation, 86 DESIGN, CONSTRUCTION, OPERATION, ETC. 1/8 inch lead sheath. Normal current 242 amperes. What is resultant carrying capacity with 200 amperes sheath current ? D = 2 .61, d = 2 .36, D 2 - d 2 = 1 .25. ., 0/lo /, 4 (.2116) (.684) (.43) Resultant carrying capacity = 242 -u 1 -- ^ -' = .893 (242) = 216 amperes. In a similar way the reduction of current carrying capacity for certain cables has been calculated in Tables 1 to 4. Tables 1,2, and 3 are for single conductor cables for 250 volt, 2,300 volt, and 600 volt service, respectively. Table 4 is for 13,200 volt, 3 conductor cables. The normal ampere rating in the second column of Tables 1 and 2 for rubber insulation is based on the following formula. Wherein the following terms are used : di = diameter of copper in inches. d z = diameter over insulation in inches. dz = diameter over sheath in inches. K = resistivity of insulation in degrees C. rise per watt per inch cube. J = radiation resistivity of lead sheath to ambient sur- roundings in degrees C. rise per watt per inch square. r = resistance of conductor at 7\, per inch length. / = current carrying capacity of cable. T l = permissible copper temperature, in degrees C. T 2 = temperature of ambient surroundings in degrees C. In solving the formula, the following values of the several con- stants were taken : . K = 300C. rise per watt per inch cube. J = 200C. rise per watt per inch square. T 2 = 40C. The normal ampere rating in tables 3 and 4 for paper insula- tion is based on the data in the paper entitled "High-Tension, Single-Conductor Cable for Polyphase Systems," by W. S. Clark and G. B. Shanklin, Transactions of the A. I. E. E., 1919, Vol. XXXVIII, page 917. DESIGN, CONSTRUCTION, OPERATION, ETC. 87 The conductor temperatures used are in practical agreement with Rule 9100, page 95, Revision of 1921 of the Standards of the American Institute of Electrical Engineers. Where different normal ampere ratings or temperatures are used, the percentages of normal current that can be carried with various sheath currents will differ from those given in these tables. Naturally, the effect of sheath currents is greater for small and medium sized cables, and it may be noted that cables of these sizes and types are most commonly met in complicated distribu- tion networks. Also, for the same size conductor, a given sheath current will reduce the current carrying capacity of the cable to a lesser extent as the insulation thickness is increased. In cases where drainage must be employed and where heating is a factor, the sheath currents can be reduced to a minimum by limiting the drainage to the smallest values which will protect the system. TABLE 1. EFFECT OF SHEATH CURRENTS ON ALLOWABLE CONDUCTOR CURRENT OF SINGLE CONDUCTOR 250-VOLT 2/32" RUBBER INSULATION. SHEATH AS- SUMED 1/16" THICK. Conductor size Normal ampere rating at 60 C. Conductor temp. 40 ambient Per cent of normal rating which can be carried with sheath currents as indicated 10 amp. 20 amp. 30 amp. 40 amp. 50 amp. No. 6.... 4 2 1/0*. . 56 75 101 137 96.0 96.8 97.7 98.3 83.0 86.6 90.2 93.0 54.3 66.0 76.0 83.0 49! 5 66.8 37.2 * Thickness insulation = 5 /64' TABLE 2. EFFECT OF SHEATH CURRENTS ON ALLOWABLE CONDUCTOR CURRENT OF SINGLE CONDUCTOR 2,300-VOLT 6/32" RUBBER INSULATION. SHEATH AS- SUMED 3/32" THICK. Normal Conductor ampere rating at 60C-.25E Per cent of normal rating which can be carried with sheath currents as indicated. size Conductor temp. 40 ambient. 10 amp. 20 amp. 40 amp. 50 amp. 60 amp. 70 amp. No. 6.... 60 99.2 96.2 90.9 82.7 71.9 55.5 23.5 4 79 99.2 96.5 92.0 85.3 75.8 62.2 34.6 2 106 99.3 97.3 93.7 88.5 81.0 71.0 57.1 1/0 139 99.4 97.6 94.4 89.5 83.0 74.3 62.6 88 DESIGN, CONSTRUCTION, OPERATION, ETC. TABLE 3. EFFECT OF SHEATH CURRENTS ON ALLOWABLE CONDUCTOR CURRENT OF SINGLE CONDUCTOR 600-VOLT 4/32" PAPER INSULATED CABLES. SHEATH ASSUMED 1/8" THICK. Normal Per cent of normal rating which can be carried with sheath Conductor ampere rating at currents as indicated. size 85C Conductor temp. 50" amp. 75 amp. 100 amp. 125 amp. 150 amp. 175 amp. 200 amp. 250.000 c.m. 510 97.8 96.4 91.0 85.5 78.3 68.7 55.7 500,000 c.m. 720 98.0 95.7 92.2 87.5 81.5 73.6 63.3 750,000 c.m. 880 98.3 96.3 93.3 89.4 84.3 77.8 69.7 1,000.000 c.m. 1,010 98.5 96.7 94.0 90.3 85.7 80.0 72.7 1,500,000 c.m. 1,250 98.8 97.2 94.5 91.8 88.0 83.3 77.5 2,000,000 c.m. 1,440 98.8 97.3 95.4 92.7 89.3 85.0 80.0 TABLE 4. EFFECT OF SHEATH CURRENTS ON ALLOWABLE CONDUCTOR CURRENT OF ROUND THREE CONDUCTOR 13,200-VOLT 6/32 BY 6/32 PAPER INSULATED CABLES DUE TO STRAY CURRENTS FLOWING ON SHEATH. SHEATH AS- SUMED 1/8" THICK. Conductor size Normal ampere rating at 75 C. Conductor temp. Per cent of normal rating which can be carried with sheath currents as indicated 50 amp. 75 amp. 100 amp. 125 amp. 150 amp. 175 amp. 200 amp. 1/0 2/0 173 193 218 242 263 290 312 99.3 99.3 99. 99. 99. 99. 99. 98.4 98.4 98.5 98.5 98.6 98.6 98.7 97.3 97.2 97.3 97.5 97.6 97.8 97.7 95.6 95.6 95.5 95.5 96.2 96.5 96.4 93.5 93.5 94.0 94.0 94.4 95.0 94.8 91.2 91.3 91.8 91.3 92.3 93.0 93.0 88.3 88.4 89.1 89.3 89.8 90.7 90.6 3/0 4/0 250,000 c.m.. 300.000 c.m.. 350.000 c.m.. Good duct construction with vitrified clay or fibre conduit for laterals and main conduits, and the draining of manholes to sewers or by sumps will tend to increase the resistance of the cables to earth, and thereby reduce the tendency to collect stray currents. On the other hand, thorough grounding of sheaths is in many cases resorted to as a protective measure for isolated sections. Where it is impossible to protect cable systems by natural drainage, boosters have occasionally been used to artificially lower the potential of the cable system. This practice, as well as the over drainage of cable systems, is objectionable where other underground structures are involved as it may result in unusually high potential differences between the piping and cable systems with resulting damage to the pipes. 2. Difference Between Cable Drainage and Pipe Drainage. The early use of drainage as a method of affording protection against electrolysis of lead covered cables led to the proposal to DESIGN, CONSTRUCTION, OPERATION, ETC. 89 apply the same method of protection to underground piping systems. The result is that more or less pipe drainage has been used, particularly on water systems and to a limited extent on gas systems. While the success of protecting cable systems by drainage is generally recognized, there are important differences in the application of drainage to cables and to piping systems which make the application of drainage to the latter difficult and uncertain. Among the important differences between the drainage of cable and piping systems are : 1. Cables are electrically continuous and uniform conductors, while pipes are not uniform conductors and are sometimes dis- continuous conductors due to the joints in them. Experience indicates that in mains having cement joints a large percentage of these joints are of high resistance, and in mains having lead joints, occasional joints of very high resistance are found and many of the joints have resistances higher than several lengths of pipe. -Therefore, drainage will lower the potential of the pipe for relatively short distances from the drainage taps, so that to be effective a greater number of drainage taps must be installed than for a cable system of the same extent. The number and location of taps will depend upon the extent and physical layout of the pipe network, and the expense involved will depend upon the number and locations of the taps required. 2. Under certain conditions there is a tendency for current flowing on a pipe to leave it on the positive side of a high resistance joint, returning to the joint on the negative side, or else to flow to another structure. As a result of this, joint corrosion may occur at high resistance joints unless both sides of the joint are main- tained negative or neutral to the adjacent earth at all points and under all conditions; and conversely, no electrolytic corrosion will occur on either side of a high resistance joint if the entire surface of both the adjacent pipe lengths is permanently negative to the surrounding earth. The difficulty of keeping a complicated network of pipe negative to the adjacent earth by means of drainage is much greater than in the case of cable systems. 3. Cable systems are placed in ducts with manholes conveniently spaced so that the effect of the application of drainage to a cable system may be adjusted so as to produce the results desired, whereas with pipes buried in the ground, and in large cities beneath improved pavements, it is more difficult to make the necessary measurements to ascertain the effects of drainage. 4. Cables are relatively small and contained in ducts so that 90 DESIGN, CONSTRUCTION, OPERATION, ETC. unless they are in wet or marshy ground, they are but partially in contact with the earth, whereas, gas or water pipes are buried directly in the earth. Because of this condition, the drainage of an underground piping system with, but few high resistance joints results in the flow of larger amounts of current than does the drainage of a cable system. 5. Currents flowing in piping systems conveying inflammable substances, such as gas or oil, constitute a fire and explosion hazard and many cases have been reported where stray currents have caused arcs which have ignited the gas or oil when the continuity of the pipe was broken. One of the objections to the presence of excessive currents on gas or oil pipes is the necessity for bonding around a cut in the pipe whenever a pipe is opened for repairs. Under such conditions a copper wire cable is con- nected around the point on the pipe to be opened. Jumper cables, terminating with adjustable clamps are used by some companies for this purpose. Under certain conditions there is also danger of increasing potential differences between service pipes in confined air spaces which may result in causing arcs due to the intermittent contact between pipes which will puncture the gas pipes and ignite the escaping gas. 3. Application of Drainage to Pipes. (a) Maintaining Pipes Negative to Earth. Investigations of the Research Subcommittee show that when electrical drainage feeders are connected to a jointed piping system the drained pipe is maintained negative to the soil for only a few hundred feet from the point of connection. In such cases it is necessary to extend the drainage feeder along the principal pipes in the positive area, which extends theoretically about 40 per cent of the distance from the supply station to the end of the feeding district, and connect to the pipes at frequent intervals. (b) Effect of Pipe Drainage on Current Interchange. Various conditions exist in piping systems which tend to affect the inter- change of current between them, and these should be fully recog- nized in the consideration or employment of pipe drainage. If a single pipe system exists, as for example, a water system in a small town, the drainage of that system will not as a rule result in objectionable interchange between various parts of the network. However, there are usually several piping systems present, such as a lead calked water pipe system and a lead calked gas pipe sys- tem. If these piping systems are not interconnected at many DESIGN, CONSTRUCTION, OPERATION, ETC. 91 points through appliances, or are not otherwise connected together, the drainage of one or both systems might result in serious inter- change of current. The application of drainage to one piping system in a territory where another piping system exists may result in an interchange of current between the drained and undrained systems so it is necessary to resort to the common drainage of all of the piping systems to be protected, as the potential inequalities created by separate drainage cause electrolysis at points where the current leaves the undrained system to find its path to the drained system. Even with the most carefully installed and maintained unified system of drainage, it cannot be expected that all danger from current interchange will be eliminated. Pipe systems laid with cement joints, Dressser Joints, or other high resistance joints and not interconnected with other systems, will usually need no other form of protection against electrolysis. If, however, such a system exists in a territory also occupied by a piping system with lead calked joints and connected to it at many points through applicances or otherwise, the service pipes of the system with the high resistance joints and the sections of the mains to which they are connected, will be electrically connected to the more continuous system and so far as electrolysis is concerned should be considered as a part of that system. Any electrolysis condition existing on the continuous system will therefore be experienced by such service pipes and the sections of the mains of the discontinuous system as connect directly with it and any measure which tends to protect the continuous piping system will also affect the services of the discontinuous system. This con- dition is illustrated in Fig. 18, where a continuous water piping system is connected through appliances to gas services. Although the gas mains are laid with cement joints, they are being damaged by current brought to them over the water mains. The application of pipe drainage under conditions here de- scribed may afford protection to some portions of the piping system and increase the damage to others. In some areas gas services and water services are connected with each other through appliances so that at these locations the two piping systems are maintained at practically the same potential. In most piping networks, however, there will be extensive areas where the gas and water systems are not interconnected by such appliances and even where they do exist they cannot always be relied upon to maintain the two systems at practically the same potential. 92 DESIGN, CONSTRUCTION, OPERATION, ETC. (c) Effects of Different Kinds of Pipe and Joints. A fundamental difficulty in applying electrical drainage to piping systems is usually present and this is the great variation of conductivity of different kinds of pipes and of different joints. In any cast iron piping system the resistance of the joints varies through wide limits. In many cities there are a number of different kinds of pipes in use: steel mains with welded or screw joints have a low resistance; steel mains with gaskets made of rubber are high in resistance, while cast iron mains with cement joints are unusually high in resistance. With electrical drainage the current on the pipes is increased and the potential drop along these pipes and over the joints is increased in like proportions. Because of these conditions it is difficult to apply drainage without increasing the potential differences between the different piping systems at some points. SUMMARY OF GOOD PRACTICE This summary is intended only as an annotated index or guide to the contents of Chapter 2 of this report, not as a substitute. Before forming an opinion or taking even preliminary action on any subject treated in the report the full text should be studied. A. RAILWAYS 1. Track Construction and Bonding. (See Page 25.) (a) The use of heavy rails with joints properly bonded and well maintained is the first requirement for good track conductivity and the minimizing of stray currents. (b) In paved streets welded rail joints are regarded as the best and most permanent form of bonding. (c) Rail joints including three feet of rail which have a resistance in excess of 10 feet of adjacent rail should be rebonded, except joints bonded with long bonds, which should be renewed when the resistance exceeds that of 15 feet of adjacent rail. (d) Bonded joints should be tested at least once each year and such tracks as show bond failures in excess of 5 per cent annually should be tested every six months. A failure is here defined as exceeding the resistance specified in paragraph (c). (e) Cross bonds, connecting the two rails on single track, and the four rails on double track should be installed at intervals not to exceed 500 feet in city systems and from 1,000 to 2,000 feet on interurban lines. DESIGN, CONSTRUCTION, OPERATION, ETC. 93 (f) Jumpers of one or more conductors should be used around all special work, and should connect to all rails on both sides of the special work. The size of such jumpers should be proportioned to the current on the rails, but in no case should they be smaller than No. 0000 for one track. In addition, where practicable, all special track work should be bonded and maintained as other track rails. 2. Track Insulation. (See Page 31.) (a) In the construction of electric railway tracks and roadbeds the electrolysis problem should be given consideration with economy of construction, maintenance, and operation. (b) Roadbeds should be constructed with as high electrical resistance to earth as consistent with other considerations, special attention being given to keeping them dry by drainage. Where practicable, rails should be kept out of contact with the earth. (c) Clean crushed stone ballast offers a much greater electrical resistance to stray current than does solid concrete as a foundation under ties. (d) Where crushed stone or gravel ballast is used it should be kept clean. If earth, sand, or street dirt is permitted to filter into ballast of this character its insulating property is greatly impaired. Vegetation should be kept down, as this tends to make the roadbed moist and to fill the ballast with foreign material. (e) Salts, which are often used to prevent freezing at switches and frogs, greatly reduce the resistance of roadbeds and should be avoided as much as possible. (f) Zinc chloride and similar chemical tie preservatives reduce, while creosote and gas oil increase the electrical resistance of ties. 3. Reinforcement of Rail Conductivity. (See Page 32.) Copper is not economically employed when connected in parallel with tracks, and therefore subjected to the same voltage drop as exists on the tracks, as it cannot be loaded to capacity with track voltage drops ordinarily permissible. Buried copper conductors or old rails used to supplement the track return also increase the contact area between the return circuit and the earth and thereby tend to augment stray currents. For these reasons the use of such supplementary conductors should be avoided. 94 DESIGN, CONSTRUCTION, OPERATION, ETC. 4. Power Supply. (See Page 33.) (a) Power supply stations for electric railways should be located with consideration to their effect on overall potentials and potential gradients in the tracks. (b) In selecting locations for substations, particularly for interurban lines, consideration should be given to the extent and character of the underground* metallic structures in their im- mediate vicinities. (c) Connections to tracks in wet locations or the installation of bare track feeders in earth or in water courses should be avoided. (d) Numerous independent connections to the track for the return of current aff KEY TO CALCULATION OP VOLTAGE DROP IN RAILS Fig. 33. roads influence each other, inasmuch as equalizing currents will flow between their rail networks. Deviations in both directions from these potentials can be justified by certain circumstances in case of especially good EUROPEAN PRACTICE 169 conditions of the ground, that is to say, in very dry dirt an increase of the potentials may be permissible. But even in such cases it is advisable to be cautious in allowing such an increase, so as not to violate the rules as given in paragraph 5. Where the conditions are unfavorable, for instance, where moist ground of especially high conductivity prevails, it is advisable, to remain below the limits. For railroads with brief daily operation concessions have been made because damage to the pipes depends upon the dura- tion of the influence of the current so that, considering the short time of operation, even greater currents cannot cause any appreci- able damage to the pipes. For railroads of three hours daily operation double drop in potential is allowed, while for railroads of one hour operation, four times the drop is permissible. Wherever the rail network is not sufficient to carry the current without exceeding the per- missible potential in the network, the whole plan for the return of the current must be altered, and improvement will be reached by providing return cables in which, if necessary, resistances or boosters may be inserted. The resistances should be variable so as to correspond with the variable conditions of service and opera- tion. In cases where the railroad system is fed from several power plants a reduction of the drop in potential in the rails may be brought about by shifting the loads of the several power plants. The arrangement of the cables and resistances can be made in so many different ways as to make a general rule for all cases impossible. It is recommended to investigate thoroughly the cases under observation, because considerable saving in the con- struction and operation of the plant may be achieved by a careful layout. The keeping of the return points at the same potential is recom- mended as a precautionary measure but not required. The same offers a certain guarantee of the possibility of keeping the differ- ence of potential within the 2.5 v. limits. Furthermore, the use of the three- wire system with the rails as a neutral conductor is worthy of consideration. In this system the difference of potential in the rails depends on the distribution of the positive and negative feeder districts. This distribution again depends on the local conditions of the plant, so that no general rules can be given in regard to it. Alterations of the conditions of operation can be counteracted by switching the load to the positive or negative side of the system. The rules do not recommend any certain system, but 170 EUROPEAN PRACTICE leave it entirely to the projecting engineer to select the one best adapted to existing conditions. The damage to pipes takes place mostly at points of low potential on two-wire railroads, in the neighborhood of the return points ; and on three- wire railroads, in the districts of negative feeders; because it is mainly here that the current leaves the pipes. It is advisable to place the return points of the negative feeder districts whenever possible in loca- tions with dry ground of low conductivity and as far as possible from such pipe lines as are of importance for. the water and gas supply. The permissible limits of differences in potential in rails must not exceed, either according to calculations or at the practical trial, the limits given in Section 1, of these rules. The measure- ment of the difference in potential is made by means of test wires as called for in Section 6. The measurements of differences in potential are limited to those points which, according to calcu- lations, come nearest to the established limits. Wherever long lines, as, for instance, telephone wires, are available, it is advisable to use them for these measurements otherwise several test wires may be connected in series or temporary test lines may be in- stalled. Finally, the restilts of single measurements may be computed to reach the same final results. Only high resistance voltmeters should be used for these measurements so as to make the resistances of the test wire and .contacts negligible. The pointers of these instruments should have the slowest movements and a good damper arrangement, so as to give good readings even under strong fluctuations. For all measurements only average values are considered. All measurements are to be extended over a full period of operation which results from the average frequency of trains. Section 4. Resistance Between Rail and Earth The resistance between ground and the rail which is used for carrying the return current should be kept as high as possible. When the conditions of the ground or the situation of the track are not favorable for this purpose, the resistance should be in- creased by a special effective insulation. The rails or any conductor connected to the rails must not be in contact with the pipes or any kind of metal buried in the ground. Furthermore, care must be taken that the distance between the nearest rail and any metallic part of the pipe lines or connections to them which project above the ground or lie EUROPEAN PRACTICE 171 near the surface, be kept as great as possible, and should never be less than one meter. Stationary motors, lighting installations or any other plant which receives current from a railway system which uses the rails for carrying the return current, must be connected to the rail network by means of insulated conductors. Excepted are short connections of not more than 16 square millimeters which are not deeper than 25 centimeters in the ground and which are at a dis- tance of at least 1 meter from any part of a pipe network. These connections may be of bare metal. In order to increase the resist- ance between rail and ground it is recommended to use a bedding of high resistance and to provide good drainage, also to render the bedding water-tight to the roadbed for a sufficient width on both sides of the rail. The use of salt for the melting of snow and ice, should be limited to cases of absolute necessity. Wherever sufficient distance between the rail and such parts of the pipe line as project above the surface is not obtainable, it is advisable to change the pipe run, or where this is not possible, to use insulating strata (such as vitrified clay, masonry or wooden conduits, etc. Explanation The magnitude of currents passing into the ground depends not only on the potentials in the rail network, but also on the resistances between the rails and the pipes and on the resistances of the pipe lines themselves. It will always be of advantage to increase the resistance of the ground between the rails and the pipes. An artificial increase of the resistances of the pipe line can 'be achieved for instance, by the use of insulating flanges, couplings, etc. Aside from the technical difficulties of installing such insulating parts into gas pipes, and especially water pipes with a high pressure, and of insuring their lasting tightness, it would be difficult to provide these insulating pieces in the necessary numbers and to take care of their correct distribution. A wrong arrangement of the same will lead to an extraordinary concentra- tion of currents at these insulations with consequent corrosion in these places. A greater part of the drop in potential between pipe and rail originally takes place in the roadbed as can be easily understood and it is therefore required to render this resistance as high as possible by the good insulation of the roadbed, good drainage, etc., and to maintain it thus. 172 EUROPEAN PRACTICE In the same measure that the increase of the resistances between rail and pipe is recommended, the use of any means to reduce these resistances, is to be warned against. Such means to be considered are ground plates, connections of metals in the ground, and espe- cially metallic connections between the rails and the pipes. The last will reduce the density of the current at the point of connec- tion to the pipe, but they cause an increase of the pipe current and of the ground currents in general which may cause damage in other places, as, for instance, at interruptions in the pipe line or at crossings with other lines. Any local measure taken must be considered with regard to its effect on the pipes in other localities. Metallic connections between different pipe networks also are to be judged from this viewpoint. Immediate contact of any parts of the pipe lines with the rails, or too close an approach, has the same effect as direct metallic connections and is, therefore, to be avoided. (By a relocation of rails or pipes or installation of insulating strata). Especially in cases of stationary motors or lighting plants connected to the railroad system, there exists on the premises danger of an accidental or deliberate connection or contact with the pipe lines. It is, therefore, necessary to have strict rules regarding the return cables from such plants. Section 5. Current Density The above rules are intended to prevent the destruction of the pipes by electrolysis. The rate of destruction is in direct propor- tion to the amount of current leaving the pipe. Any pipe line where the current leaving the pipe exceeds an average density of 0.75 milliampere per square decimeter and where this current is due to a railway, may be considered en- dangered by this railway, and further preventive measures must be taken. For railways with freight service when the service is of com- paratively short duration, exceptions as already mentioned are permissible. In cases where the current leaving or passing into the pipes changes its direction, the current passing into the pipe must be taken as nil when determining the average density, until further experience has been gained in this matter. Explanation Inasmuch as a total elimination of all damages to pipes would be in most cases possible only at a disproportionately high cost, EUROPEAN PRACTICE 173 which would far exceed the cost of any possible damage to the pipes, it is necessary to allow a certain limited damage, that is to say, a damage which is of little practical importance and which does not noticeably shorten the life of the pipes. These rules have therefore been compiled on the basis of the average conditions, that is to say, such as are mostly met with, and it is to be expected according to previous experience that the damage done to pipe lines by the stray currents from electrical railways generally will remain limited to the practical allowable limit wherever these rules are observed. Under exceptionally bad conditions, that is to say, under conditions which very much favor the origin of stray cur- rents, greater corrosion of pipes in certain places can hardly be avoided, even if the limits of the drop in the potential in the rails, as laid down in Section 3, are not exceeded. It is, therefore advisable to establish some measure for the elimination of imme- diate danger to the pipes. For the judgment of the damage attributed to a railroad system the density of the current leaving the pipes and returning to the railroad system is indicative. The density of the current at the pipe can be measured only after the completion of the plant. These measurements must be made during the time of operation,. as per schedule, and as de- scribed in Section 3. The average density is important and is obtained from the computation of the results of several measure- ments, each of which follows a whole period of service. Measurements of current density can be made, for instance, by means of a milliammeter and non-polarizable frame as designed by Prof. Haber. This frame contains two copper plates which are insulated from each other and which for the prevention of polariza- tion are covered with a paste of copper sulphate and 20 per cent sulphuric acid, over which a parchment, soaked with sodium sul- phate is laid. The frame is filled with dirt except between the plates, and placed alongside the pipe at right angles to the as- sumed direction of the current and then covered with dirt. A very sensitive ammeter connected to the copper plates will indi- cate the current passing through the frame and the density of this current can readily be calculated by taking into account the surface of the copper plates inside the frame. Inasmuch as here also only average readings are to be considered, it is advisable to use an instrument with very slow period. According to investigations made so far, absolute danger to the pipes results whenever the density of the currents leaving the 174 EUROPEAN PRACTICE pipes reaches the average value of 0.75 milliampere per square decimeter. For railroads with small periods of operation an excess up to double and quadruple, respectively, the above value is permissible according to the rules laid down in Section 3. Wherever the direction of the current changes, the current entering the pipes are not to be considered in the calculations of the average density, inasmuch as it is not yet established that such currents will add to the metal of the pipes. Wherever the average values are exceeded, special precautionary measures are to be taken, the nature of which can be determined only by the local conditions. In many cases it is sufficient to protect a very limited section of the rail network, to which end the further reduction of the drop in the rails may not be necessary, but which may be attained by other means as, for instance, the re-location of short sections of tracks or pipes, or the artificial increase of the' resistances between rails and pipes at such points. In all cases the question arises whether the railroad is to be considered as the only cause of current concentration, as other causes may be found to be responsible for a part of the current on the pipes; for instance, bare neutrals or poor insulation in other electrical systems, the natural electrical elements resulting from the use of different metals in the pipe lines, or from different chemicals in solution in the ground. That part of the current which is attributable to the influence of the railroad can be deter- mined by comparison with the measurements of the current during the period of no operation. In many cases the influence of the railroad can be judged from contemporaneous measurements of current density and the potential between pipe and rail. Under certain circumstances it is possible to find the degree of influence of the railroad and of other electrical plants operating at the same time, by establishing the course of the current in the ground. For this investigation electrodes that cannot be polarized are used as contacts from the test line to the ground. The measurements should preferably be made by the potentiometer method in order to eliminate drop at the electrodes due to the current flow, but this method is difficult in practice on account of the rapid fluctua- tions of the voltage. It will be sufficient in most cases to make the measurements with a voltmeter of very high resistance so that the current passing through the electrodes will be very small. It should be emphasized that such measurements should be made by experts only, as deviations from the right method which seem of no importance often give useless results. EUROPEAN PRACTICE 175 Section 6. Control. In order to be able to test the potential at the return points of the rail system of a given territory, pilot wires are to be connected to these points and carried to a central testing place. Before a service may be increased the potential distribution in the rail network must be retested. The rail bonds and bridge connections are to be retested once yearly by means of a suitable rail joint tester and must be ar- ranged so that they fulfill the rules of Sections 1 and 2. Con- nections, the resistance of which has been found greater than that of an uninterrupted rail of ten meters length, must be repaired to comply with these rules. Explanation. The control of the drop in potential in the whole network would be best assured by the installation of test wires from one of the buses to all points of probable highest and lowest rail potential, which arrangement admits of immediate measurement of poten- tial between these points. In certain cases, especially in existing plants, the installation of such test wires would involve great cost. Such test wires from all of the important rail points were not required; but it has been ruled that all points of the rail network, to which cables of the same district are now connected,, are to be provided with test wires which have to run to some central point where readings of the differences of potentials between the return points can be taken. Wherever the expense involved permits, it is recommended to install test wires not only to the return points but also to the points of highest rail potentials. After permanent changes in the operation, the distribution of the potential in the rail network is to be investigated in the same way as after the inauguration of the plant, in order to ascertain whether the new conditions still correspond to the rules. In case of temporary changes of short duration in the whole network or parts of the same as, for instance, occasionally some festival, change or repair of tracks, fairs, exhibits, etc., no special measures are to be taken because the short duration of the influ- ence will cause no noticeable damage even when the limits of these rules are exceeded. The yearly investigation of the rail joints, as required by the rules, is also to be recommended with regard to the reduction of 176 EUROPEAN PRACTICE losses of energy. For these measurements an apparatus may be used which allows of the comparison of the drop in potentials across the joint with one of the adjoining uninterrupted rails so that the measurement may be taken during the operation. Joints of a resistance higher than that of an uninterrupted rail of 10 m. length are immediately to be repaired. The total resistance, as found by the measurement of the single joints, must not exceed the value which has been assumed during the projection of the plant (compare Section 2, paragraph 2). Should it result during operation that rail joints are of a higher resistance than that assumed in the designing, it is permissible to abstain from a reconstruction of the joints as long as the permissible difference of potentials in the rails is not exceeded, even with these higher resistances. The established limits of 20% increase of the resistance of the uninterrupted rail by the bonds must not be exceeded in any case. FRANCE REGULATIONS BY MINISTER OF PUBLIC WORKS CIRCULAR AND ORDER OF THE MINISTER OF PUBLIC WORKS (FRANCE) OF MARCH 21, 1911, ESTABLISHING THE TECHNICAL CONDITIONS WHICH ELECTRICAL DISTRIBUTION SYSTEMS MUST SATISFY IN ORDER TO CONFORM TO THE LAW OF JUNE 15, 1906. Regulations Relative to the Construction of Structures for Electric Railways Using Direct Currents. Right of Way. When the rails are used as conductors, all necessary measures should be taken to guard against the harmful action of stray cur- rents, on metallic structures, such as the tracks of railways, the water and gas pipes, the telegraph or telephone lines and all other electric conductors, etc. To this end the following regulations shall be applied: 1. The conductance of the tracks shall be known to be in the best possible condition, especially in regard to the joints, whose resistance should not exceed, in each case, that of 10 meters of the normal track. The management is required to verify periodically this con- ductance and to place the results obtained on file, which shall be accessible to the administration upon demand. 2. The drop in potential in the rails, measured upon a length of track of 1 kilometer taken arbitrarily upon any section of the system, should not exceed an average value of 1 volt for the operat- ing period of the normal car schedule. 3. The feeders tied into the track shall be insulated. EUROPEAN PRACTICE 177 4. Where the tracks contain switches or crossings, the conduct- ance shall be maintained by special work. 5. When the track crosses a metallic structure, it should be electrically insulated, as much as possible, throughout the length of the structure. 6. As long as no metallic structure is in the neighborhood of the tracks, a drop in potential greater than that fixed in paragraph 2 may be allowed, upon the condition that no damage will result, and particularly no trouble to telegraphic or telephonic communi- cation, and none to railway signals. 7. The owner of the distribution system shall be required to make the installations necessary to enable the administration to verify the fulfillment of the provisions of this article; it should particularly provide, whenever necessary, for pilot wires to be installed between designated points of the distribution system. Protection oj Neighboring Aerial Lines At all points where the lines feeding the traction system cross other distribution lines, or telegraph or telephone lines, the sup- ports should be established with a view to protect mechanically these lines against contact with the aerial conductors feeding the traction system. In all cases, measures shall be taken to prevent the trolley wire touching the neighboring lines. ENGLAND BRITISH BOARD OF TRADE REGULATIONS REGULATIONS MADE BY THE BOARD OF TRADE UNDER THE PROVISIONS OF SPECIAL TRAMWAYS ACTS OR LIGHT RAILWAY ORDERS AUTHORIZING "LINES" ON PUBLIC ROADS; FOR REGULATING THE USE OF ELECTRICAL POWER; FOR PREVENTING FUSION OR INJURIOUS ELECTROLYTIC ACTION OF OR ON GAS OR WATER PIPES OR OTHER METALLIC PIPES, STRUCTURES OR SUBSTANCES; AND FOR MINIMIZING AS FAR AS IS REASONABLY PRACTICABLE INJURIOUS INTERFER- ENCE WITH THE ELECTRIC WIRES, LINES, AND APPARATUS OF PARTIES OTHER THAN THE COMPANY, AND THE CURRENTS THEREIN, WHETHER SUCH LINES DO OR DO NOT USE THE EARTH AS A RETURN. FIRST MADE, MARCH, 1894. REVISED, APRIL, 1903. FURTHER REVISED, AUGUST, 1904. FURTHER REVISED, MAY, 1908. FURTHER REVISED, APRIL, 1910. FURTHER REVISED, SEPTEMBER, 1912. Regulations 1. Any dynamo used as a generator shall be of such pattern and construction as to be capable of producing a continuous current without appreciable pulsation. 178 EUROPEAN PRACTICE 2. One of the two conductors used for transmitting energy from the generator to the motors shall be in every case insulated from earth, and is hereinafter referred to as the "line"; the other may be insulated throughout, or may be uninsulated in such parts and to such extent as is provided in the following regulations, and is hereinafter referred to as the "return." NOTE: The Board of Trade will be prepared to consider the issue of regulations for the use of alternating currents for electrical traction on application. 3. Where any rails on which cars run or any conductors laid between or within three feet of such rails form any part of a return, such part may be uninsulated. All other returns or parts of a return shall be insulated, unless of such sectional area as will re- duce the difference of potential between the ends of the uninsulated portion of the return below the limit laid down in Regulation 7. 4. When any uninsulated conductor laid between or within three feet of the rails forms any part of a return, it shall be elec- trically connected to the rails at distances apart not exceeding 100 feet by means of copper strips, having a sectional area of at least one-sixteenth of a square inch, or by other means of equal conductivity. 5. (a) When any part of 'a return is uninsulated it shall be connected with the negative terminal of the generator, and in such case the negative terminal of the generator shall also be directly connected, through the current-indicator hereinafter mentioned, to two separate earth connections which shall be placed not less than 20 yards apart. (b) The earth connections referred to in this regulation shall be constructed, laid and maintained, so as to secure electrical contact with the general mass of earth, and so that, if possible, an electromotive force, not exceeding four volts, shall suffice to produce a current of at least two amperes from one earth con- nection to the other through the earth, and a test shall be made once in every month to ascertain whether this requirement is complied with. (c) Provided that in place of such two earth connections the Company may make one connection to a main for water supply of not less than three inches internal diameter, with the consent of the owner thereof, and of the person supplying the water, and provided that where, from the nature of the soil or for other reasons, the Company can show to the satisfaction of the Board of Trade that the earth connections herein specified cannot be EUROPEAN PRACTICE 179 constructed and maintained without undue expense, the provi- sions of this regulation shall not apply. (d) No portion of either earth connection shall be placed within six feet of any pipe except a main for water supply of not less than three inches internal diameter, which is metallically connected to the earth connections with the consents hereinbefore specified. (e) When the generator is at a considerable distance from the tramway the uninsulated return shall be connected to the negative terminal of the generator by means of one or more insulated return conductors, and the generator shall have no other connection with earth ; and in such case the end of each insulated return connected with the uninsulated return shall be connected also through a current indicator to two separate earth connections, or with the necessary consents to a main for water supply, or with the like consents to both in the manner prescribed in this regulation. (/) The current indicator may consist of an indicator at the generating station connected by insulated wires to the terminals of a resistance interposed between the return and the earth con- nection or connections, or it may consist of a suitable low-resist- ance maximum demand indicator. The said resistance, or the resistance of the maximum demand indicator, shall be such that the maximum current laid down in Regulation 6 (I) shall produce a difference of potential not exceeding one volt between the ter- minals. The indicator shall be so constructed as to indicate cor- rectly the current passing through the resistance when connected to the terminals by the insulated wires before-mentioned. 6. When the return is partly or entirely uninsulated the Com- pany shall in the construction and maintenance of the tramway (a) so separate the uninsulated return from the general mass of earth, and from any pipe in the vicinity; (b) so connect together the several lengths of the rails ; (c) adopt such means for reducing the difference produced by the current between the potential of the uninsulated return at any one point and the potential of the uninsulated return at any other point; and (d) so maintain the efficiency of the earth connections specified in the preceding regu- lations as to fulfill the following conditions, viz: (I) That the current passing from the earth connections through the indicator to the generator or through the resist- ance to the insulated return shall not at any time exceed either two amperes per mile of single tramway line or five per cent of the total current output of the station. (II) That if at any time and at any place a test be made 180 EUROPEAN PRACTICE by connecting a galvanometer or other current-indicator to the uninsulated return and to any pipe in the vicinity, it shall always be possible to reverse the direction of any current indicated by interposing a battery of three Leclanche cells connected in series if the direction of the current is from the return to the pipe, or by interposing one Leclanche cell if the direction of the current is from the pipe to the return. The owner of any such pipe may require the Company to permit him at reasonable times and intervals to ascertain by test that the conditions specified in (II) are complied with as regards his pipe. 7. When the return is partly or entirely uninsulated a con- tinuous record shall be kept by the Company of the difference of potential during the working of the tramway between points on the uninsulated return. If at any time such difference of potential between any two points exceeds the limit of seven volts, the Com- pany shall take immediate steps to reduce it below that limit. 8. The current density in the rails shall not exceed nine am- peres per square inch of the cross-sectional area. 9. Every electrical connection with any pipe shall be so arranged as to admit of easy examination, and shall be tested by the Com- pany at least once in every three months. 10. Trie insulation of the line and of the return when insulated, and of all feeders and other conductors, shall be so maintained that the leakage current shall not exceed one hundredth of an ampere per mile of tramway. The leakage current shall be as- certained not less frequently than once in every week before or after the hours of running when the line is fully charged. If at any time it should be found that the leakage current exceeds one- half of an ampere per mile of tramway, the leak shall be localized and removed as soon as practicable, and the running of the cars shall be stopped unless the leak is localized and removed within 24 hours. Provided that where both line and return are placed within a conduit this regulation shall not apply. 11. The insulation resistance of all continuously insulated cables used for lines, for insulated returns, for feeders, or for other pur- poses, and laid below the surface of the ground, shall not be per- mitted to fall below the equivalent of 10 megohms for a length of one mile. A test of the insulation resistance of all such cables shall be made at least once in each month. 12. Any insulated return shall be placed parallel to and at a distance not exceeding three feet. from the line when the line and EUROPEAN PRACTICE 181 return are both erected overhead, or eighteen inches when they are both laid underground. 13. In the disposition, connections, and working of feeders, the Company shall take all reasonable precautions to avoid in- jurious interference with any existing wires. 14. The Company shall so construct and maintain their sys- tem as to secure good contact between the motors and the line and return, respectively. 15. The Company shall adopt the best means available to prevent the occurrence of undue sparking at the rubbing or rolling contacts in any place and in the construction and use of their generator and motors. 16. Where the line or return or both are laid in a conduit the following conditions shall be complied with in the construction and maintenance of such conduit. (a) The conduit shall be so constructed as to admit of examination of and access to the conductors contained therein and their insulators and supports. (b) It shall be so constructed as to be readily cleared of accumulation of dust or other debris, and no such accumula- tion shall be permitted to remain. (c) It shall be laid to such falls and so connected to sumps or other means of drainage, as to automatically clear itself of water without danger of the water reaching the level of the conductors. (d) If the conduit is formed of metal, all separate lengths shall be so jointed as to secure efficient metallic continuity for the passage of electric currents. Where the rails are used to form any part of the return they shall be electrically connected to the conduit by means of copper strips having a sectional area of at least one-sixteenth of a square inch, or other means of equal conductivity, at distances apart not exceeding 100 feet. Where the return is wholly insulated and contained within the conduit, the latter shall be connected to earth at the generating station or sub-station through a high resistance galvanometer suitable for the indication of any contact or partial contact of either the line or the return with the conduit. (e) If the conduit is formed of any non-metallic material not being of high insulating quality and impervious to mois- ture throughout, the conductors shall be carried on insulators, the supports for which shall be in metallic contact with one another throughout. 182 EUROPEAN PRACTICE (/) The negative conductor shall be connected with earth at the station by a voltmeter and may also be connected with earth at the generating station or substation by an adjust- able resistance and current-indicator. Neither conductor shall otherwise be permanently connected with earth. (g) The conductors shall be constructed in sections not exceeding one-half a mile in length, and in the event of a leak occurring on either conductor that conductor shall at once be connected with the negative pole of the dynamo, and shall remain so connected until the leak can be removed. (h) The leakage current shall be ascertained daily, before or after the hours of running, when the line is fully charged and if at any time it shall be found to exceed one ampere per mile of tramway, the leak shall be localized and removed as soon as practicable, and the running of the cars shall be stopped unless the leak is localized and removed within 24 hours. 17. The Company shall, so far as may be applicable to their system of working, keep records as specified below. These records shall, if and when required, be forwarded for the information of the Board of Trade. Number of cars running. Number of miles of single tramway line. Daily Records. Maximum working current. Maximum working pressure. Maximum current from the earth plates or water-pipe connec- tions (vide Regulation 6 (&)) where the indicator is at the generat- ing works. Fall of potential in return (vide Regulation 7). Leakage current (vide Regulation 16 (h)). Weekly Records. Leakage current (vide Regulation 10). Maximum current from the earth plates or water-pipe connec- tions (vide Regulations 6 (I)) where a maximum demand indicator is used. Monthly Records. Condition of earth connections (vide Regulation 5) . Minimum insulation resistance of insulated cables in megohms per mile (vide Regulation 11). EUROPEAN PRACTICE 183 Quarterly Records. Conductance of connections to pipes (vide Regulation 9). Occasional Records. Specimens of test made under provisions of Regulation 6 (II). Board of Trade, 7, Whitehall Gardens, S. W. September, 1912. SPAIN ELECTRIC LEGISLATION LAW OF MARCH 23, 1900. TO PREVENT THE RETURN CURRENT OF ELECTRIC TRAMWAY LINES FROM EXERCISING ANY ELECTROLYTIC EFFECTS, THE FOLLOWING MEASURES SHALL BE TAKEN: (1) The rails of each one of the tracks are bonded by weld- ing or by connections formed of short copper cables or of equivalent cables made of some other metal, the section of which having to exceed 100 square millimeters per track, and shall be made as large as possible. (2) At intervals of 100 meters, or at shorter distances the tracks shall be cross-bonded. (3) In case the official inspector should deem it necessary, a cable will have to be stretched in every line, which will have to be intimately connected with both tracks, and (4) The dimensions of all cables and wires constituting such system will have to be calculated upon a basis that the potential difference between the generator terminals and the point of the tracks remotest from them will not exceed an amount of seven volts. CHAPTER 5. ELECTROLYSIS RESEARCH FURTHER WORK NECESSARY TO ARRIVE AT AN ENGINEERING SOLUTION OF THE PROBLEM The Committee's conception of an engineering solution of the electrolysis problem is that the railway system and the systems of underground structures shall be so designed, constructed, main- tained, and operated, that the entire problem, caused by the presence of stray currents in the earth, including corrosion of structures, fire and explosion hazards, heating of power cables, and operating losses and difficulties, is solved in the most economi- cal way. 1. Methods of Testing. The Research Sub-committee of the American Committee on Electrolysis, in its investigations, has been constantly confronted with the difficulty that available methods of electrolysis testing do not yield directly, definite information as to the electrolytic con- dition of the affected structures. An electrolysis survey, to be conclusive must, in some cases, show the true polarity of pipe or cable with respect to earth and in other cases it must show the actual density of the current flowing from pipe to earth in any particular locality under investigation, but to determine such polarity, or intensity of current flow, is very difficult. The exist- ing methods of making electrolysis surveys include, among others, measurements of potential differences between pipes and earth, but such measurements, as ordinarily made, are often quite mis- leading. At the present time, therefore, the results that follow the application of any particular method of electrolysis mitiga- tion are sometimes open to question because of the lack of ade- quate test methods. It is evident therefore, that the development of improved means of electrolysis testing whereby the actual cur- rent density of discharge from pipes to earth at any point can be measured is an important preliminary step toward securing definite information on which the solution of the outstanding questions relating to electrolysis protection can be based. The Research Sub-committee now has under investigation certain new methods of electrolysis testing which offer considerable promise in this direction and it is felt that a thorough study and development of 184 ELECTROLYSIS RESEARCH 185 these should be made in the hope of obtaining improved test methods and equipment that will facilitate securing the informa- tion required. It is desirable that these investigations precede further experimental work relating to methods of mitigation. 2. Effect of Different Rail Voltage Drops. It is important to examine the resulting conditions, from an electrolysis standpoint, of different values of voltage drop in rails, particularly in cities or localities where such voltage drops are low, and comparable to those which correspond to maximum economy from the railway standpoint, taking due account of variations in physical conditions in different localities. 3. Studies of Electric Railway Power Distribution. Studies should be made of the costs of various measures de- signed to minimize track drops in order to determine which measures, if any, are best to apply. The application of auto- matic and semi-automatic substations to street railways should be given consideration to determine how far the voltage drop in the rails can be reduced with such a system when developed to the economic limit. In making these cost studies track net- works should be selected where the layout is both favorable and unfavorable for such installations. Studies might also be made of the joint application of insulated negative feeders and auto- matic substations to determine what values of voltage drops in the rails can be obtained at reasonable cost. 4. Study of Mitigative Measures Applicable to Affected Structures. After applying mitigative measures to the railway system, it may be found that in many cases it will still be necessary to reduce further the hazards to underground structures. It is therefore important to study methods of mitigation applicable to the struc- tures themselves, and particularly the quantitative effect of insulating joints in protecting pipes and cables and the applica- tion and maintenance of such a drainage system as will keep all underground structures negative to the earth without involving fire and explosion hazards, and assuming in both cases the railway stray current at a low value. 5. Determination of Safety Criterion for Pipes Where Positive to Earth. At the present time there is no reliable criterion as to the actual hazard to underground pipes unless they are at all points negative or neutral to earth at practically all times. Wherever pipes are 186 ELECTROLYSIS RESEARCH positive to earth, it is impossible with the present methods of testing to determine the actual degree of corrosion hazard. If however, the development work in connection with methods of measuring current discharge from pipes mentioned in a preceding paragraph should result favorably, it appears probable that such test methods could be used for the purpose of establishing a fairly accurate criterion for a safe condition of underground structures. The Committee feels that this question should be investigated carefully so that anything possible of accomplishment in this direction may be realized. 6. Self Corrosion. When iron pipes are embedded in certain soils, corrosion due to soil conditions or local galvanic action often results in greater or less degree. This phenomenon is commonly known as self corro- sion. Obviously, it is of importance to differentiate between the effects of corrosion due to the action of chemicals in the soil and that due to stray currents, in order that an intelligent procedure can be adopted for remedying the trouble. It is believed that a thorough and systematic study of the question of soil corrosion on cast iron, wrought iron and steel pipes would bring to light information that would be of great value in dealing with the electrolysis problem. Such investigations in order to be of much value should be extended over a period of years. 7. Fire and Explosion Hazards on Gas and Oil Pipes. In addition to preventing corrosion, there is the closely related problem of protecting against fires and explosions due to electric currents on gas or oil pipes. At the present time no definite information is available as to what limiting currents can safely be permitted on such pipe systems. It is important to investigate this question, both statistically and experimentally in order to evaluate this hazard. 8. Heating of Power Cables Due to Stray Currents on Sheaths. In view of the fact that it is common practice to electrically drain the lead sheaths of power cables to protect them from corro- sion, and since the currents on the sheaths may be of considerable magnitude, reducing the current carrying capacity of the conduc- tors, it is important to determine the limitations that should be imposed on such currents in order not to cause serious heating, and hence undue reduction in current carrying capacity of the cables. ELECTROLYSIS RESEARCH 187 Summary. As the Committee now views it, a research of some magnitude is necessary to secure further information needed for an engineering solution of the problem, to comprise the following: 1. Development of practical means for measuring current density across contact surfaces of pipes and earth. Such measurements are especially necessary if structures are not kept negative to earth. 2. Development of practical means for accurately deter- mining the polarity of structures and adjacent earth, in such a way as to eliminate galvanic effects. 3. Study of the relation of different values of voltage drop in the track to stray current from rails, including the large variations of this relation under different conditions, and the effects of such stray currents on underground utilities and railway structures. 4. Cost studies of street railway systems and different methods of power supply to determine the minimum values of track voltage drop consistent with economic operation in various locations. 5. Quantitative effect of insulating joints in protecting pipes and cables, assuming railway stray current at low values. 6. Detailed study of the application and maintenance of such a drainage system as will keep all underground struc- tures negative to earth. Such studies to include the effect of drainage on corrosion of subsurface and railway structures and its effect on producing fires and explosions. 7. Comparison of 5 and 6. 8. Investigation of the distribution of current flowing from pipe to adjacent earth for the purpose of determining whether a diversity factor can be established, i.e., the relation between maximum and average current density. 9. Continuing study of joint corrosion. 10. Study of soil and galvanic corrosion with particular reference to differentiating them from the effects of stray currents. 11. Setting limit of current on gas and oil pipes to avoid fire and explosion hazard. 12. Setting limit of current on power cable sheaths to avoid overheating. BIBLIOGRAPHY In compiling the following bibliography no attempt has been made to list the literature on the subject of electrolysis in its 188 ELECTROLYSIS RESEARCH entirety. This bibliography may be considered as a selected list of such contributions to the subject known to the committee as in its opinion are of the most importance at the present time. The committee, however, does not sponsor the articles here listed nor does it present them as comprising a complete discussion of the subject. General Corrosion of Iron Pipes by Action of Electric Railway Currents. Dugald C. Jackson. Journal of Association of Engineering Societies, September, 1894. Electrolytic Corrosion of Iron by Direct Current in Street Soils. Albert F. Ganz. Trans. A. I. E. E., Vol. XXXI, page 1167. 1912. Stray Currents from Electric Railways. Carl Michalke. Trans- lated and edited by Otis Allen Kenyon, McGraw Publishing Company, New York, N. Y. 1906. Electrolytic Corrosion of Iron in Soils. Burton McCollum and K. H. Logan. Bureau of Standards Technologic Paper No. 25, June, 1913. Effects of Electrolysis on Engineering Structures. Albert F. Ganz. Trans. International Engineering Congress, San Francisco, 1915. Electrolysis and Its Mitigation. E. B. Rosa and Burton Mc- Collum. Bureau of Standards Technologic Paper No. 52, Nov., 1918. Electrolysis, Troubles Caused Thereby and Remedies That May be Applied. Albert F. Ganz, Journal New England Water Works Association. Vol. XXXI, No. 2, 1917. Report of Gas Association Committee on Electrolysis. J. D. Von Maur, Chairman. Technical Section Sessions, American Gas Association, 1919. Electrolytic Corrosion of Pipes and Cables Destructive Effect of Electric Currents on Subterranean Metal Pipes. Isaiah H. Farnham, Trans. A. I. E. E., 1894. Electrolysis of Water Pipes. Charles A. Stone and Howard C. Forbes. New England Water Works Association, Vol. 9, 1894-5. Topical Discussion on Electrolysis. Proc. New England Water Works Association, Vol. XX, 1905. Earth Resistance and Its Relation to Electrolysis of Underground Structures. Burton McCollum and K. H. Logan. Bureau of Standards Technologic Paper, No. 26. ELECTROLYSIS RESEARCH 189 Surveys and Measurements Measuring Stray Currents in Underground Pipes. Carl Hering. A. I. E. E., June, 1912, pp. 1147-61. Electrolysis Surveys. Albert F. Ganz. Engrg. Rec., 1908, V. 57, p. 261. Methods of Making Electrolysis Surveys. Burton McCollum and G. H. Ahlborn, Bureau of Standards Technologic Paper No. 2&, 1916. Bureau of Standards Studies return Circuit Conditions in Milwau- kee. E. R. Shepard. Elec. Ry. Journal, April 19, 1919, pp. 770-772. Electrolysis Surveys and Their Significance. Report of the 1920 Electrolysis Committee of the American Gas Association, L. A. Hazeltine, Chairman. Technical Section Sessions. Alternating Current and Periodic Current Electrolysis Alternating-Current Electrolysis. J. L. R. Hay den. Trans. A. I. E. E., 1907. Vol. 26, part I. Influence of Frequency of Alternating or Infrequently Reversed Current on Electrolytic Corrosion. Burton McCollum and G. H. Ahlborn. Bureau of Standards Technologic Paper No. 72, 1916. Discussion of McCollum and Ahlborn Paper, New York. March 10, 1916. Proc. A. I. E. E. July, 1916. Electrolytic Corrosion of Lead by Continuous and Periodic Cur- rents. E. R. Shepard. American Electro-chemical Society, 1921. Reinforced Concrete Corrosion of Iron Embedded in Concrete. Guy F. Schaffer. Engineering Record, July 30, 1910. Electrolytic Corrosion of Iron and Steel in Concrete. A. A. Knudson. Trans. A. L E. E., v. 26, part 1, p. 231. Electrolysis in Concrete. E. B. Rosa, Burton McCollum, and O. S. Peters. Bureau of Standards Technologic Paper No. 18, Mar., 1913. Preventing Electrolysis of Iron in Concrete. W. A. Delmar and D. C. Woodbury. Electrical World, November 10, 1917. Track Construction, Track Leakage, and Rail Bonding Modern Practice in the Construction and Maintenance of Rail Joints and Bonds in Electric Railways. E. R. Shepard, Bureau of Standards Technologic Paper No. 62, 1920. 190 ELECTROLYSIS RESEARCH Leakage of Currents from Electric Railways. Burton McCollum and H. K. Logan, Bureau of Standards Technologic Paper No. 63, 1916. Data on Electric Railway Track Leakage. G. H. Ahlborn, Bureau of Standards Technologic Paper No. 75, 1916. Leakage Resistance of Street Railway Roadbeds and its Relation to Electrolysis of Underground Structures. E. R. Shepard. Bureau of Standards Technologic Paper No. 127. 1919. Insulated Negative Feeders Means for Preventing Electrolysis of Buried Metal Pipes. Isaiah H. Farnham. Cassiers Magazine, August, 1895. Some Theoretical Notes on the Reduction of Earth Currents from Electric Railway Systems, by Means of Negative Feeders. George I. Rhodes Trans. A. I. E. E., Vol. XXVI, p. 247, 1907. Special Studies in Electrolysis Mitigation II. E. B. Rosa, Burton McCollum and K. H. Logan. Bureau of Standards Tech- nologic Paper No. 32, 1913. Special Studies in Electrolysis Mitigation III. Burton McCollum and G. H. Ahlborn. Bureau of Standards Technologic Paper No. 54, 1916. Electrolysis from Stray Electric Currents. Albert F. Ganz. Trans. A. I. E. E., Vol. XXXI, p. 1167, 1912. Automatic Substations Automatic Substations on the North Shore Line. C. H. Jones, Electric Railway Journal, Jan. 11, 1919, 53: 84-90. Year of the Automatic Substation at Butte. E. J. Nash, Electric Railway Journal, March 22, 1919. 53: 565-7. Second Year of Automatic Substation Operation at Butte. E. J. Nash, Electric Railway Journal, Jan. 24, 1920. 55: 202. Automatic Railway Substations. F. W. Peters: Journal A. I. E. E March, 1920. 39:267-74. Excerpts Elec. Ry. Journal, March 13, 1920. 55:518-19; Abstract Elec. Ry. Journal, June 13, 1920. 55:519-21. Experience Shows Economy of Automatic Operation. Electrical World, March 20, 1920. Automatic Stations for Heavy City Service. R. J. Wensley, Journal A. I. E. E., April, 1920. pp. 359-364. Automatic Substations at Des Moines. F. C. Chambers, Elec. Ry. Journal, April 10, 1920, 55:738-44. ELECTROLYSIS RESEARCH 191 The Automatic Substation in Electrolysis Mitigation. E. R. vShepard, Electric Railway Journal, April 30, 1921. Three- Wire Operation Three-wire System in Los Angeles. S. H. Anderson, Electric Railway Journal. February 26, 1916. Line Drops and Rail Potentials Reduced by Three- Wire System in Omaha. E. H. Hagensick, Elec. Ry. Journal, November 10, 1917. Sectionalization of Overhead Wire for Three-Wire Operation. E. R. Shepard, Elec. Ry. Journal. December 8, 1917. Electrolysis Mitigation in Winnipeg. W. Nelson Smith, Elec. Ry. Journal, March 26, 1921. Insulating Pipe Coverings Comparative Values of Various Coatings and Coverings for the Prevention of Soil and Electrolytic Corrosion of Iron Pipe. Robert B. Harper, Proc. Illinois Gas Association. Vol. 5, 1909. Also American Gas Light Journal, v. 91, 1909. Insulation of Pipes as a Protection Against Electrolysis. Albert F. Ganz., Engineering Record, 1909, V. 60, p. 582. Also Pro. Am. Gas Inst. about same date. Surface Insulation of Pipes as a Means of Preventing Electrolysis. Burton McCollum and 0. S. Peters, Bureau of Standards Technologic Paper No. 15, 1914. Insulating Joints Insulating Couplings for Protecting Pipe Systems from Elec- trolysis. William Brophy and A. R. Gray, Am. Gas Light Journal, 1904, V. 80, p. 91. Flexible High Pressure Pipe Joint. Engrg. Rec., V. 62, p. 307. 1910. Cement Joints for Cast Iron Water Mains in Los Angeles. Cement World, February, 1916. Pipe and Cable Drainage Bonding Lead Covered Cables to Prevent Electrolysis. W. G. Middleton. Elec. Rev. and West Electrn., V. 57, p. 423. 1910. Drainage if Necessary vs. Negative Feeder Electrolysis Protection. D. W. Roper, Elec. Ry. Journal, Dec. 7, 1918. 192 ELECTROLYSIS RESEARCH Discussion of preceding articles. Elam Miller, H. C. Button, and D. W. Roper, Elec. Ry. Journal, April 5, 1919. Legal Aspects The Law Relating to Conflicting Uses of Electricity and Electroly- sis. George F. Deiser. T. & J. W. Johnson Co., Phila- delphia, Pa. 1911. Electrolysis of Underground Conductors. George F. Sever. Trans. International Electrical Congress, Vol. 3, p. 666. 1904. APPENDIX TABLE 5 CURRENT DATA FOR STEEL RAILS* Based on a resistivity of 0.0003 ohm per pound-foot, this being equivalent to about 11 times the resistivity of copper. Weight . (Ibs. per yd.) Current for 1m. v. on 1 ft. (amperes) Weight (Ibs. per yd.) Current for 1 m. v. on 1 ft. (amperes) 60 66.7 110 122.0 65 72.2 115 128.0 70 77.8 120 133.0 75 83.3 125 139.0 80 88.9 1 130 144.0 85 94.4 135 150.0 90 100.0 140 156.0 95 106.0 145 161.0 100 111.0 150 167.0 105 117.0 * Does not include rail joints. TABLE 6A CURRENT DATA FOR PIPES CAST IRON A.W.W.A. standard A.W.W.A. standard Class A Class B Nominal inside diameter Current Current (inches) Weight for 1 mv. Weight for 1 mv. pounds on 1 ft. pounds on 1 ft. per foot (amperes) per foot (amperes) 3 13.04 10.6 14.60 11.9 4 18.03 14.7 20.06 16.4 6 27.90 22.7 31.14 25.4 8 38.74 31.6 42.68 34.8 10 51.95 42.3 58.80 47.9 12 66.90 55.0 76.44 62.0 14 82.33 67.0 94.82 77.0 16 98.75 81.0 114.70 94.0 18 118.10 96.0 137.70 112.0 20 137.2 112.0 163.20 133.0 24 186.5 152.0 217.10 177.0 30 265.1 216.0 312.6*0 255.0 36 357.8 292.0 419.00 341.0 42 465.6 379.0 541.50 441.0 48 607.7 495.0 688.50 562.0 54 730.2 596.0 842.80 685.0 60 835.6 680.0 1,012.00 826.0 72 1,169.0 952.0 1,416.00 1,150.0 84 1,141.0 1,177.0 1,860.00 1,515.0 193 194 APPENDIX TABLE 6A (Continued) CAST IRON A.W.W.A. standard A.W.W.A. standard Class C. Class D. Nominal Inside Diameter Current Current (inches) Weight for 1 mv. Weight for 1 mv. pounds on 1 ft. pounds on 1 ft. per foot (amperes) per foot (amperes) 3 15.47 12.6 16.37 13.2 4 21.27 17.3 22.83 18.5 6 32.93 26.8 35.30 28.8 8 47.97 39.1 51.16 41.7 10 65.66 - 54.0 71.54 58.0 12 85.26 70.0 93.59 76.0 14 108.0 88.0 119.1 97.0 16 133.3 109.0 147.5 120.0 18 162.4 132.0 178.4 145.0 20 190.9 156.0 212.4 173.0 '24 257.7 210.0 286.2 233.0 30 367.5 300.0 421.4 344.0 36 499.8 407.0 580.7 474.0 42 656.6 535.0 762.0 621.0 48 833.0 680.0 960.4 780.0 I 54 1,041.0 848.0 1,227.0 1,000.0 60 1,220.0 990.0 1,458.0 1,190.0 72 1,744.0 1,430.0 APPENDIX 195 TABLE 6A (Continued} CAST IRON New England W.W.A. New England W.W.A. standard Class A. standard Class B. Nominal inside diameter Current Current (inches) Weight for 1 mv. Weight for 1 mv. pounds on 1 ft. pounds on 1 ft. per foot (amperes) per foot (amperes) 4 14 89 12.1 6 24.32 19 9 8 35.58 29.0 10 49.04 40.0 52^03 "42:i' 12 61.14 50.0 65.92 54.0 14 76.85 63.0 82.41 67.0 16 90.98 74.0 98.95 81.0 18 104.5 85.0 115.2 94.0 20 121.9 99.0 133.7 109.0 24 155.6 127.0 174.4 142.0 30 215.3 176.0 244.8 200.0 36 287.0 234.0 326.0 266.0 42 368.4 300.0 422.1 344.0 48 459.3 374.0 530.2 432.0 54 559.8 456.0 650.3 530.0 60 664.0 541.0 782.3 640.0 196 APPENDIX TABLE 6A (Continued] CAST IRON New England W.W.A. Standard Class C. New England W.W.A. Standard Class D. Nominal Inside Diameter Current Current (inches) Weight for 1 mv. Weight for 1 mv. pounds on 1 ft. pounds on 1 ft. per foot (amperes) per foot (amperes) 4 15.7 12.8 6 26.72 21.8 8 40.38 32 9 10 54.99 44.8 57.94 47.2 12 70.67 58.0 75.39 61.0 14 87.97 72.0 94.85 77.0 16 106.9 87.0 114.8 93.0 18 127.4 104.0 138.0 112.0 20 147.6 120.0 161.4 132.0 24 196.3 160.0 215.3 175.0 30 277.7 226.0 307.3 250.0 36 373.3 304.0 412.3 336.0 42 481.1 392.0 538.9 439.0 48 608.0 495.0 678.9 552.0 54 749.5 610.0 839.9 684.0 60 911.5 740.0 1,029.7 840.0 APPENDIX 197 TABLE 6B STEEL PIPE XT " 1 Standard Extra Strong Nominal inside diameter (inches) Weight pounds Current for 1 mv. on 1 ft. Weight pounds Current for 1 mv. on 1 ft. per foot (amperes) per foot (amperes) 0.125 0.24 1.11 0.31 1.44 0.25 0.42 1.95 0.54 2.50 0.375 0.57 2.64 0,74 3.43 0.50 0.85 3 94 1 09 50 0.75 1.13 5.2 1.47 6.8 1 00 1 68 7.8 2.17 10.1 1 25 2.27 10.5 3.00 13.9 1.50 2.72 12.6 3.63 16.8 2.00 3.65 16.9 5.02 23.3 2.50 5.79 26.8 7.66 35.5 3.00 7.58 35.1 10.25 47.5 3.50 9.11 42.2 12.51 58.0 4.00 10.79 50.0 14.98 69.0 4.50 12.54 58.0 17.61 82.0 5.00 14.62 68.0 20.78 96.0 6.00 18.97 88.0 28.57 132.0 7.00 23.54 109.0 38.05 176.0 8.00 24.70 114.0 43.39 201.0 8 00 28 55 132 9.00 33.91 157.0 "48'73 226.0 10.00 31.20 145.0 54.74 254.0 10.00 34.24 159.0 10.00 40.48 188.0 11.00 45.56 211.0 60.08 278.0 12.00 43.77 203.0 65.42 303.0 12.00 49.56 230.0 13.00 54.57 253.0 72.09 334.0 14.00 58.57 271.0 77.43 359.0 15.00 62.58 290.0 82.77 383.0 198 APPENDIX TABLE *6C WROUGHT IRON PIPE Standard Extra Strong Nominal Inside diameter (inches) Weight pounds Current for 1 mv. on 1 ft. Weight pounds Current for 1 mv. on 1 ft. per foot (amperes) per foot (amperes) 0.125 0.24 1.15 0.29 1.39 0.25 0.42 2 01 0.54 2.58 0.375 0.56 2.68 0.74 3.54 0.50 0.84 4.02 1.09 5.2 0.75 1 12 5.4 1.39 6.6 1.0 1.67 8.0 2.17 10.4 1,25 2.25 10.8 3.00 14.3 1.50 2.69 12.9 3.63 17.4 2.0 3.66 17.5 5.02 24.0 2.50 5.77 27.6 7.67 36.7 3.0 7.54 36.0 10.25 49.0 3.50 9.05 43.3 12.47 60.0 4.0 10.72 51.0 14.97 72.0 4.50 12.49 60.0 18.22 87.0 5.0 14.56 70.0 20.54 98.0 6.0 18.76 90.0 28.58 137.0 7.0 23.41 112.0 37.67 180.0 8.0 25.00 120.0 43.00 206.0 8.0 28.34 136.0 9.0 33.70 161.0 48.73 233.0 10.0 32 00 153 10.0 35.00 167.0 10.0 40.00 191.0 "54^74 "262.Q 11.0 45.00 215.0 60.08 287.0 12 45 00 215 12.0 49.00 234.0 65.42 313.0 APPENDIX 199 TABLE 6D A. G. I. Standard Gas Nominal inside diameter (inches) Weight pounds per foot Current for 1 mv. on 1 ft. (amperes) 4 17.3 14.1 6 27.3 22.2 8 38.0 30.9 10 51. 0* 41.5 12 67.0 55.0 16 102.0 83.0 20 139.0 113.0 24 186.0 152.0 30 256.0 209.0 36 346.0 282.0 42 453.0 369.0 48 610.0 405.0 TABLE 6E LEAD PIPE Current for Specimen No. Card diameter (inches) Card weight (Ibs. per ft.) 1 mv. drop per ^foot (amperes) 1 0.25 0.5 0.915 2 .25 .5 .908 3 .25 .5 .942 4 .75(AA) 3.5 7.257 5 .75(AA) 3.5 7.332 6 .75(AA) 3.5 7.305 7 .75(AA) 3.5 7.123 8 .75(AA) 3.5 7.148 9 .75(AA) 3.5 7.067 10 .00(C) 2.5 4.914 11 .00(C) 2.5 4.921 12 .00(C) 2.5 4.958 13 .00 (A A) 4.75 9.785 14 .OO(AA) 4.75 9.833 15 .OO(AA) 4.75 9.766 16 2.00(C) 6.0 11.81 17 2.00(C) 6.0 11.78 18 2.00(C) 6.0 11.77 19 2.00(AA) 9.0 18.14 20 2.00(AA) 9.0 18.11 21 2.00(AA) 9.0 18.11 22 .25 .5 .915 23 .25 .5 .913 24 .25 .5 .915 25 .75(C) 1.75 3.302 26 75(C) 1.75 3.343 27 .75(C) 1.75 3.322 200 APPENDIX IDtlQ papuoq Q V c/j uo jo UOI4D3JIQ ti o APPENDIX 201 2 * *a c V 1 8 .s B c 5 i rt .2 H CURRENT MEASUREMENTS DIREC- TION ! a O < c is K i ' Drop Millivolts I ::::::::::: 1 : : :::::::: if ::::::::::: ::::::::: ^ 1^1 | ::::::::: .a'B.ll R