Cotnell XDlnivetsit^ OF-THE IRew ^ovh State dollegc of Hfiriculture .xa^Adi. 3..:^;xl:^u Cornell University Library TK 3201.B8 Electric wiring, 3 1924 003 609 561 Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003609561 ELECTRIC WIRING BY JOSEPH a BRANCH, B.S., M. E. Author of ' Stationary Engineering," "Conversa- tions on Electricity,'" "Practical Electricity," "Gespraeche ueber Elektrizitaet," "Engineers' Chart Book," "Heat and Light from Municipal and Other Waste," Etc. Former Member of the Board of Examining Engineers for the City of St. Louis, Inspector Boilers and Elevators and Chief Engineer, Etc. Member of the Amer- ican Society of Mechanical Engineers, Etc. CHICAGO BRANCH PUBLISHING COMPANY 1910 Coyright, 1910, by JOSEPH G, BRANCH. IV Preface THE object of the author in writing this book is to make clear the principles which gov- ern the art of wiring, using only such wir- ing tables as are in daily practical use to demon- strate these principles. The experimental stage in electric wiring has been passed, and mere compilations of tables no longer satisfy the student in this field of electrical work; nor, do they now meet the requirements of the prac- tical, wireman, the electrician, or the contractor. They wish to know the principles upon which the formulae used by them are based, so that they can make for themselves such tables as needed by them in their daily work. We are indebted to Ohm and Helmholtz almost entirely for all the fundamental principles used in the art of electric wiring ; and, it has been the sole ob- ject of the author to present these principles in a clear and concise manner, so that anyone using wir- ing tables in his daily work can become a master not only of the mechanical part of his work, but also of the ART itself. For this reason, the author has treated alternating current phenomena as a part of electric wiring, so that the fundamental formulae used in such work can be more readily understood; and, also that the distinction between direct current wiring and alter- nating current wiring can be more clearly brought out. As no book would be complete without embracing the principal requirements of The National Board of Fire Underwriters, the author has embraced such Code requirements as tend to make the wireman and the contractor better informed, and tnore thoroughly imbued with the need of care and accuracy in all electric wiring. July, 1910. JOSEPH G. BRANCH. VI CONTENTS. CHAPTER I.— PAGE 1. Dynamic Electricity. The Electric Circuit. Ohm's Law. CHAPTER II.— PAGE 11. Energy, Work and Power. Measurement of Energy. Work and Power. Electric Power. Classes of Circuits. Series Connections. Multiple-Series or Series-Multiple Connections. Series Circuit. Parallel or Multiple Circuits. Machines in Series and in Parallel. Connection of Voltmeter and Ammeter in Circuit. CHAPTER III.— PAGE 34. Purpose of Wiring. Drop of Potential. Meaning of a Circular Mil. Meaning of a MiLfoot. Calculation of Drop. CHAPTER IV.— PAGE 52. Effect of Heat upon Resistance. Allowance for Heat. Carrying Capacity of Wires. A Simple Electric Light Circuit. VII CONTENTS. CHAPTER v.— PAGE 74. Elements of a Wiring System. Definition of Main, Feeders and Branches. Proportioning the Drop in the System. Equalizing the Pressure. CHAPTER VI.— PAGE 89. Systems of Wiring. The Three-Wire System. CHAPTER VII.— PAGE 101. Methods of Wiring. Reasons for Employing Conduit; Rigid Conduits; Flexible Conduits. Armored Cables. Flexible Tubing. Cleat or Insulators. Moulding. CHAPTER VIII.— PAGE 125. Conductors. Insulation. Insulators. CHAPTER IX.— PAGE 135. Construction and Code Requirements of Fuses and Safety Devices. CHAPTER X.— PAGE 149. Cut Out Panels and Cabinets. CHAPTER XI.— PAGE 154. Outlet Boxes. Outlet Insulators. VIII CONTENTS. CHAPTER XII.— PAGE 162. The Alternating Current. For Lighting and tor Power. Calculating of Alternating Current Circuits. CHAPTER XIII.— PAGE 203. Overhead Line "Work. Underground Line Work. CHAPTER XIV.— PAGE 218. Testing. Use of the Magneto. Lightning Arresters. CHAPTER XV.— PAGE 234. Annunciator Work. Wiring in Telephony. Telegraphy. Wireless Telegraphy. Surface Railways. Elevated Railways. Interurban Railways. Motor Work for Factories. CHAPTER XVI.— PAGE 263. Wiring Tables. IX LIST OF ILLUSTRATIONS. Figure Page 1. Cells in Series 18 2. Cells in Parallel or Multiple 20 3. Cells in Multiple Series 22 4. Lamps in Series 18 5. Lamps in Parallel or Multiple 20 6. Connections of Ammeter and Voltmeter 25 7. Shunt Machines in Series 27 8. Series Machines in Series 28 9. Shunt Machines in Parallel 30 10. Series Machines in Parallel 31 11. Compound Machines in Parallel 32 12. Knob Insulator 44 13. Porcelain Cleats 44 14. Cleats Carrying Wires 45 15. Moulding Carrying Wires 45 16. Conduit Carrying Wire 47 17. A Simple Fuse 47 18. Cartridge Fuse for Screw Connection 47 19. A "Bug" Cut-out Fuse Block 49 20. Main Line Fuse Block 49 21. A Single Pole Switch 51 22. A Double Break, Double Pole Switch 51 23. A Single 5 Lamp Circuit 63 24. 50 Lamp Circuit in Three Groups 63 25. Proper Connection of Branch Circuit 65 26. Improper Connection of Branch Circuit 65 27. Mains, Feeders and Branches 75 28. Feeders in Trolley Systems 80 29. Lamp Circuit with One Center of Distribution 82 30. Lamp Circuit with Two Centers of Distribution. ... 82 31. Wiring Diagram Limiting Drop to 4 Volts 84 32. Multiple System — Incandescent Lamps 91 34. Series System — Incandescent Lamps 91 35. Edison Three Wire System 93 36. 220 Volt Motor on Three Wire System 97 37. A Flexible Steel Armored Conductor 106 X Figure Pag« 38. An Armored Cable 106 39. Flexible Conduit 108 40. Insulating Porcelain Tubes Ill 41. Porcelain Cleats Ill 42. Cable Cleat Carrying Wires 113 44. Wiring Back 115 45. Insulator for Eack 115 46. Wooden Moulding 117 47. Minimum Dimensions of Moulding 117 48. Metal Moulding 119 49. Conductor Showing Strands 119 51. Plug Cartridge Fuse 137 52. An Open Link Fuse 139 53. Type of Cartridge Fuse 139 54. Sectional View of Cartridge Fuse 139 55. A Cut-Out Cabinet 150 56. Panel Board Plug Fuses 152 57. Panel Board with Link Fuses 152 58. A Panel Board Switch 153 59 60. Out-let Box and Cover 155 61. A Junction Box 157 62. Wave Form of an Alternating Current 164 63. Sine Curve of Generation 164 64. Arrangement of Electro-Magnets 168 65. An Bight Pole Alternator 170 66. Wave Forms Showing Broad and Blunt Poles 175 67. Wave Forms Showing Narrow Poles 175 68. Wave Forms Showing Wide Slots in Armature 175 69. Lag of Current 187 70. Alternator Coils in Two-Phase 190 71. Double Petticoat Insulator 266 72. Triple Petticoat Insulator 206 73. High Potential Insulator 209 75. Sleeve- Joint Fiber Conduit 211 76. Screw- Joint Fiber Conduit 211 77. Ground Detector for Two Wire System 220 77. (1) Clay Conduit. Ducts, Single and in Multiple. . XI Figure Page 78. Ground Detector for Three Wire Systems 222 79. A Magneto 224 80. Principle of the Lightning Arrester 228 81. Type of Lightning Arrester 230 82. Ordinary Type of Annunciator 235 83. Detaching Mechanism of Annunciator 235 84. Telephone Circuit Showing Induction Coils 239 85. A Telegraph Circuit 239 86. Type of Telegraph Insulator 241 87. Type of Telegraph (Tree) Insulator 241 88. Principle of Wireless Telegraphy 242 89. Circuit of Wireless Telegraph 243 90. Diagram of a Wireless Telegraph Station 244 91. A Bracket Support of Trolley Wire for Double- Track Eailway 250 92. Motor Starter 254 93. A Switchboard 262 XII CHAPTER ILLUSTRATIONS. Chap. n. Magnetic Field Around a Conductor. Chap. IV. Compass Needle Deflected by Current in Wire. Chap. V. Coils With and Without Core. Chap. VI. Magnetic Circuit. Chap. VII. Magnetic Whirl Around Wire. Chap. VII. Eight Hand Rule for Induction. Chap. IX. Eesistance Box. Chap. X. Rheostat. Chap. XII. Faraday's Rin%. Chap. XIV. Faraday's Dynamo. An Electric Car. XIII LIST OF TABLES. Table No. Page 1. Wiring Table for Electric Light Conductors 40 2. Eelative Eesistanee and Conductivity of Conductors 56 3. Temperature Coefficients 56 4. Currents Allowed by Fire Underwriters in Wires. . . 57 5. Resistance of Copper Wire — (5-A) Weight of Copper Wire 68-70 6. Wiring Table for Daily Use 72 7. Volts Lost at Different Per Cent Drop 73 8. Dimensions of Standard Cartridge Fuse. Knife Blade Contact 147 9. Dimensions of Standard Cartridge Fuse — Ferrule Contact 148 10. Sine, Cosine and Power Factors 197 11. Table of Decimal Equivalents 263 12. Metric System 264 13. Difference Between Wire Gauges in Decimal Parts of an Inch 265 14. Data of Concentric Laid Electric Light and Power Cables 266 15. Eesistanee of German Silver Wire. American Scale 267 16. Amperes for Motor 268 17. Amperes per Lamp and per Horse Power 272 18. Cost of House Wiring 269 19. Wiring Table for 220 Volts 270 20. Wiring Table for 500 Volts 271 21. Comparison of Centigrade and Fahrenheit Ther- uiQiueter Scales , , , . , 272 XIV CHAPTER I. Q. "What is dynamic electricity? A. It is current electricity; that is, electricity in motion. Q. Does electricity flow in a current like water, or a fluid? A. No ; there is no visible movement of the par- ticles, but we speak of a current of electrcity sim- ply for convenience. Q. How do we know when an electric current is flowing along a wire, or any other conductor? A. By its difi'erent manifestations — ^usually the heat which is generated by an electric current pass- ing along the wire or conductor. Q. Is heat always generated by the passage of an electric current along an electric conductor? A. Yes ; at times, however, it is almost imper- ceptible. If the wire is very small, and the current strong, the heat is so great that the wire becomes red hot, and is often melted. Q. By what other means can an electric current be detected? A. If an ordinary magnetic compass is placed over or under a wire, or any conductor that is carrying an electric current, even if placed at some distance from the conductor, the compass needle will turn in a direction at right angles to that in which the current is flowing. Q- What does this indicate? A. It proves that the passage of an electric cur- 2 ELECTRIC WIRING. rent through an electric conductor produces mag- netic properties in that conductor. Q. In what other way can an electric current be detected ? A. If the current is made to pass through water, it will decompose the water into its constituent gases, hydrogen and oxygen. Q. What, therefore, do these manifestations show? A. That an electric current possesses thermal (heat), magnetic and chemical properties. Q. Are there many theories as to the precise nature of an electric current? A. Yes ; but none are well established. The only one that has been clearly demonstrated is that the current does not flow inside the wire, or conductor but in the medium surrounding it. Q. Is heat transmitted jn this way through a wire or conductor? A. No; heat is transmitted inside or through the conductor itself. Q. What is the first essential before there can be a flow of an electric current? A. There must be a complete circuit or path over which it can flow. Q. What do you mean by a complete circuit ? A. It is an unbroken circuit or path from its starting point back to it again. Q. What do you mean by an open circuit? A. A circuit that is not complete, as when the two ends of the wire or conductor are not brought ELECTRIC WIRING. 3 together. Therefore, it is a broken circuit or path. Q. Are both open and closed circuits used in electrical work? A. Yes. Q. Are telephones and bells worked on an open or a closed circuit ? A. Mostly on open circuits. Q. How is telegraphy worked? A. Usually on a closed circuit. The message being sent by opening the circuit, which breaks or interrupts the flow of the current. Q. When is a cell at rest? A. When the circuit is open; that is, not com- plete. Q. If we break or open the circuit, what will be the effect? A. The flow of the current will instantly cease, [t is, therefore, for this reason that the ordinary cell is kept as much as possible on an open circuit in order to prevent waste of current. Q. What is the difference between a metallic circuit and a ground or earth circuit? A. If the path, or circuit, be made a complete circuit of metal (wire), it is then called a metallic circuit; but, if only partially of wire and the cur- rent then be allowed to flow back through the ground to the source of supply, it is called a ground or earth circuit. Metallic circuits are used almost exclusively for every character of work, except telegraphy. 4 ELECTRIC WIEIXG. Q. Upon what does the power of an electric cur- rent depend? A. On the pressure, or electro-motive force, • as it is called, under which the current flows, and the quantity of the movement of the circuit. Q. Upon what does the strength of the current depend? A. Upon the pressure, or electro-motive force, and upon the resistance of the circuit. Q- Upon what does the resistance of the circuit depend? A. Chiefly upon the size of the conductor (wire), and the material composing the conductor (wire). Q. Are there units for electrical measurements? A. Yes ; just the same as we have units for meas- uring liquids, solids, distances, etc. Q. Are these electrical units the same all over the world? A. Yes; in all civilized countries. Q. What are the chief units of electrical meas- urements ? A. The volt, which is the unit of the electric- motive force or pressure; the ampere, which is the unit of current, and the ohm, which is the unit of resistance. Q. How is electricity usually generated? A. In two ways. (1) By chemical means, as in voltaic cells; or (2) by mechanical means, as with the ordinary dynamo or generator. Q. Which of these means is now used for all practical and commercial work? ELECTRIC WIRING. 5 A. The second; that is, by the use of a dynamo or generator. Q. Does a dynamo or generator produce elec- tricity directly? A. No; it only produces pressure or electro- motive force, which force, for convenience, is des- ignated by the letters E. M. F. This E. M. F. (electro-motive force) cannot produce a current by itself, or unless an unbroken path or circuit is pro- vided for its passage. It only produces pressure to drive the ciirrent around the circuit. Q. Can we measure this pressure produced by a dynamo or generator? A. Tes; usually a voltmeter is used for this purpose. Q. Can we measure the quantity of electricity which is generated? A. Yes; just the same as we can measure the quantity of water which flows through a pipe, which we measure usually in gallons; or the quan- tity of sugar in a barrel, which is measured in pounds. The quantity of electricity which passes through a conductor, or circuit, in one second is nieasured in the same way, only it is called cou- lombs; and, the number of coulombs of electricity delivered per second is called amperes. Therefore, instead of measuring electricity in gallons, pounds or yards, we measure the pressure of the current in volts; the quantity delivered in coulombs, and the quantity delivered in one second, which deter- mines the strength of the current, in amperes. 6 ELECTRIC WIRING. Q. Why does the strength of the current depend on the quantity delivered in one second? A- Because any current, whether it is water, or any fluid, or electricity, does not flow all at one time, but it is a thing of duration. Q. Explain this more fully. A. Suppose we had a long pipe through which we pumped water. It would take some time for the water to reach the end; and, a considerable time for it to reach its full strength at the other end. _ After it has obtained its full strength it can be maintained indefinitely. Just so it is with a flow of electricity. The entire current does not flow over the conductor (wire) instantly, but it takes time for it to travel around the circuit, until it grad- ually reaches its full strength. An ampere of cur- rent, therefore, is so many coulcombs of current per second, one ampere being the flow of one coulomb in one second, Q. Upon what does the number of amperes of a current, or the amperage as it is called, depend? A. Upon the pressure (E. M. F.) or voltage, and the resistance of the conductor (wire) or ohms; one ampere being equal to one volt divided by one ohm- Q. If a dynamo generates a pressure of 100 volts "id the resistance of an incandescent lamp is 200 ohms, the strength (amperes) of the current which flows through the lamp is 100 volts divided by 200 ohms, or one-half ampere. What then is the dif- ference in the production of the pressure or voltage. ELECTRIC WIRING. 7 by a dynamo, and that of the strength, or amperage of a current? A. The voltage depends upon the capacity and speed of the dynamo, while the amperage depends upon the amount of work the current is called upon to perform, the amperage increasing as the load in- creases. Q. If you overload a dynamo, what will be the effect? A. If you overload a steam engine it will stop and usually no damage is done. If you overload a conductor (wire) with electricity, it will heat the wire and probably melt it. If you overload a dy- namo, certain portions of it will probably burn out, doing it much damage, but it will not stop running until it destroys itself. This result will be the effect of the amperage and not of the voltage. Q. Explain this more fully. A. It is the strength of the current, that is, the amperes, which heats the wire, and burns out the dynamo, and not the pressure, or volts. Different kinds of work require different current strength. The strength of the current which passes an ordi- nary 16 e. p. lamp is only one-half an ampere when the lamp is on a 110-volt circuit, while the current strength required for an arc lamp on this same circuit, ranges from three to ten amperes. On the contrary, the strength of the current employed in telephony is so small that it is hard to measure. 8 ELECTRIC WIRING. Q- What is the unit of measurement of pressure, or electro-motive force? A. One volt, vi'hieh is such a pressure or electro- motive force, as will cause a current of one ampere to flow against a resistance of one ohm. Q. What is the unit of resistance? A. One ohm. Q. What is the standard, or measure, of one ohm? A. It is the resistance of a column of mercury- one millimeter (0.03937 inch) square and 1.063 me- ters (41.85 inches) high, at the temperature of melting ice (32 degrees Fahr.). OHM'S LAW. Q. What law is based upon the relation between volts, amperes and resistance? A. Ohm's Law, so called from its discoverer. Dr. Ohm. Q. How is the law expressed algebraically? electro-motive force A- ■■ Strength of current = ■ resistance volts E or amperes = or C^ — ohms R as it is commonly expressed, in which C equals cur- rent, E equals electro-motive force expressed in volts, and R equals resistance, expressed in ohms. ELECTBIC WIRING. 9 Q. What other equations are derived from this one? E A, E^CXR) or R^ — , these terms all being C dependent upon each other. Q. What two factors enter whenever power is developed ? A. One is effort, and the other is the quantity of movement, or rate of motion. Without these two factors there is no power; the amount of power delivered being the product of these two factors. Q. Does electric power also consist of these two factors ? A. Yes; but under different names. Q. What determines the power of an electric current ? A. The product of the effort, called the poten- tial, pressure, or voltage of the current, and the quantity of the movement of the current, which is called the flow, or amperage. Q. By what term is mechanical power desig- nated ? A. By the term horse-power. Q. By what term is electric power designated? A. By the word watt, which is the product of one volt by one ampere- A watt is, therefore, often called a volt-ampere. Q. What then would be the algebraic formula to determine watts? 10 ELECTRIC WIRING. A. "W=EXC, in which W=Watts, E=volt- age and C= amperes. With this formula and the above three formulas any calculation in electricity becomes most simple. Q. Suppose we wish to know the resistance of a wire coil through which a current of 10 amperes will pass with 110 volts pressure? A. Substituting in our third formula, we have 110 R^ =11 ohms. 10 Q. We have a small motor taking 8 amperes of current at 110 volts pressure to run it; how many watts of current does it consume? A. Substituting in our fourth formula we have W=8X 110=880 watts. ELECTRIC WIRING. 11 CHAPTER II. ENERGY AND WORK. Q. Is it necessary that there must be a flow or current of electricity in order that useful work may be done? A. Yes; without motion there can be no energy, and without energy no work can be accomplished. Q. Can not electricity at rest, such as is stored in a Leyden jar, do work? A. No ; it must be in motion, for, while the elec- tricity in the Leyden jar has energy, it is what is Magnetic Field Around a Conductor. 12 ELECTRIC WIRING. called potential energy; that is, energy at rest, or in position. Q- Can we not create energy? A. No; we can neither create nor destroy it. Q. Is not the energy of the electric current which heated the wire lost? A. No ; the energy of the current produces heat, which is utilized to furnish the ordinary glow or electric lamp, and the heat from the lamp again passes back into space. Q. Is not the energy of the electric current lost when it decomposes water into hydrogen and oxy- gen gases? A. No; these gases again unite to form water, or to produce other forms of energy. Q. "When Work is done is heat always produced? A. Yes; whether it is in useful work or waste. Q. Does the flow of the electric current along a conductor (-wire) always produce heat? A. Yes; and the greater amount of heat so pro- duced in the conductor, so much the greater is the less of energy. Q. Is the heat produced by the passage of an electric current always a loss of energy? A. Yes; always in the conductor (wire) ;'and, in addition thereto, it is also a source of danger, as we shall hereafter see. ELECTRIC WIRING. 13 MEASUREMENT OF ENERGY AND WORK. Q- Can we measure energy? A. Yes; just the same as we measure eloth or sugar, only we use a different standard or unit of measurement. To measure cloth, we use a foot as our standard or unit ; while to measure sugar, we use a pound as our standard or unit of weight. Q. What standard or unit do we use to measure energy ? A. A foot-pound. Q. What is a foot-pound? A. A foot-pound is a name given to the amount of work that is done in raising a mass of one pound through a height of one foot against gravity? Q. Having now defined work and energy, what is power? A. Power is the rate at which energy is being spent; or, the rate at which work is being done; that is, the rate of expending energy in doing work. Q. State, then, the difference between work, force, energy and power. A. Force is merely a push or pull. Gravity is a force ; therefore, force can be expressed in terms of the equivalent weight in pounds. Energy can be expressed, therefore, in terms of foot-pounds; but power must be expressed in terms of the num- ber of foot-pounds per minute that is being ex- pended in work. Q. What do we mean by horse-power? A. James Watt found that the average work 14 ELECTRIC WIRING. of a horse is equivalent to raising a weight of one pound 550 feet high per second, so he fixed the amount of 550 foot-pounds per second as the value of one horse-power; which would be the same as 33,000 foot-pounds per minute, or 1,980,000 foot- pounds per hour- Q. How is the work done by all engines or mo- tors rated? A. By the standard of work done by a horse in one minute. Q. How do we measure the work done by elec- tric generators? A. In kilowatts, one kilowatt being 1,000 watts. Q. How do a horse-power and a kilowatt differ? A. One kilowatt is 1.34 times greater than one horse-power; so, one horse-power is the equivalent of 745.95 watts. Q. How many foot-pounds of work, therefore, would an electric generator of one kilowatt power do in one minute? A. It would do 44,232 foot-pounds per minute; or 2,653,920 foot-pounds per hour. Q. For convenience, how is the amount of elec- tric energy usually expressed? A. In kilowatt-hours. Q. What is a kilowatt-hour? A- It is the amount of work done by one kilo- watt in one hour. As a kilowatt is 1.34 times greater than one horse-power, a kilowatt-hour is, therefore, equivalent to 1.34 horse-power hours. ELECTRIC ^YmlNa. 15 Q. What two factors enter wherever power is developed ? > A. One is effort, and the other is the quantity of movement, or rate of motion. Without these two factors there is no power ; the amount of power delivered being the product of these two factors. Q. Upon what does the power delivered by a belt depend? A. It depends upon the power of the belt, which is the effort; and also upon its speed, which is the movement. Q. Suppose the tight side and the slack side of the belt pull equally, would there be any power? A. No; the pull is the difference between the tight side and the slack side of the belt. ELECTRIC POWER. Q. What, as we have already stated, determines the power of an electric current? A. The product of the effort, called the poten- tial pressure, or voltage of the current, and the quantity of the movement of the current, which is called the flow, or amperage. Q- And by what term is electric power desig- nated ? A. By the word watt, which is the product of one volt by one ampere. Q. What instrument is used to measure the elec- tric pressure, or electromotive force or potential, or voltage, as it is variously called. 16 ELECTRIC WIRING. A. A voltmeter, which will be described later. Q. Does the voltage used in eleictrie work vary? A. Yes, a great deal. Q. What voltage is required for house lighting? A. Usually 110 or 220 volts. Q. What voltage is used for street car work? A. Usually 500 to 550 volts. Q. Where the current is to be transmitted great distances, as fifty or one hundred miles, what volt- ages are required? A- From 6,000 to as high as 50,000 volts are often used. Q. What instrument is used to measure the quan- tity of current? A. An amperemeter, or ammeter, as it is usually called. Q. Can a current with a large amperage alone do work? A. No; to develop power there must be both voltage and amperage ; just as no power is trans- mitted by a belt which has movement only and no pull; that is, speed without any effort. Q. Is any power developed by a current having voltage alone? A. No; just as no power is developed by a belt which has effort and no movement. Q. What is meant by one watt? A. It denotes the rate at which electric energy is being supplied, and is, therefore, the unit of power. It corresponds to the foot-pound in work, ELECTEIC WIRING. 17 for it is the supply of one ampere of current at a pressure of one volt, and is, therefore, called one volt-ampere, because it is the product of these two factors. One watt, therefore, denotes the amount of electric power which is brought, or developed, by a current of one ampere flowing under a pres- sure of one volt. Q. What instrument is used to measure this elec- tric power? A- A wattmeter. CLASSES OF CIRCUITS. Q. Into how many classes can electric circuits be divided? A. Into three principal classes, viz., (1) Series Circuits, (2) Multiple or Parallel Circuits, (3) Mul- tiple-Series or Series-Multiples Circuits. Q. Is it possible to get an electro-motive force of 1,000 volts by using more than one cell? A. Yes; since we can easily get 1.3 volts out of a good cell, we would only have to connect 666 cells together in series. Q. What do you mean by connecting cells in series ? A. Connecting the cells in a row, with the posi- tive electrode of one cell connected with the nega- tive elctrode of the next cell ; that is, the zinc plates are connected to the copper plates. In Fig. 1 three cells are shown connected in series. 18 ELECTRIC WIRING. IMIflf Fig. I. Cells in Series. Fig. 4- Lamps in Series. ELECTRIC WIRING. 19 Q. While we have increased our electro-motive force to 1,000 volts by connecting these cells in series, have we increased the quantity of the cur- rent ; that is, the number of amperes of current ? A. No; it remains just the same- We have greatly increased the pressure of the current, but not the quantity or capacity of the current. Q. Would it be similar to increasing the pres- sure or head of water in a tank? A. Yes; exactly as if we had eleivated the tank a great number of feet, which, of course, would in- crease the head or pressure with which the water would be discharged; but, as long as there was no flow of water, it could not increase the amount of the discharge. Q. If we wish to increase the quantity or cur- rent capacity of the cells, that is, the amperage, how must these cells be connected? A. In parallel or multiple. Q. What do you mean by parallel or multiple connection ? A. When all the positive electrodes of the cells are connected to one main positive conductor, and all the negative electrodes are connected to one main negative conductor. When these two con- ductors are brought together, the circuit is com- plete, and the current flows with a greatly increased volume or quantity. In Fig. 2 three cells are shown connected in parallel. 20 ELECTEIC WIRING. ifill Fig. 2. Cells in Parallel. + Fig. 5. Lamps in Parallel. ELECTRIC WIRING. 21 Q. "Will the E. M- F. or voltage also be in- creased ? A. No ; it will remain exactly the same. Q. Suppose we have four cells of one volt and one-fourth ampere each connected in series, what will be the total electro-motive force, or voltage, and number of amperes of these cells? A. The electro-motive force would be increased to four volts, while the quantity or amperage of the current would remain the same. Q. Suppose we connected these same four cells in parallel or multiple what would then be the number of volts and number of amperes? A. The electro-motive force would remain the same, being one volt, but the volume or quantity of the current would be increased to one ampere. It would be similar to connecting four boilers to- gether, each boiler under a hundred pounds pres- sure, for while the total pressure of the four boilers would remain one hundred pounds, the quantity of steam generated would be four times as great. Q. Can we connect cells that are in series by a parallel connection, and thereby still further in- crease their working capacity? A. Yes; such a connection is called a multiple- series, or a series-multiple connection. Q. What is the effect of this combination of series and parallel connections? A. It gives a higher potential and a stronger current than is possible to obtain from any one cell 22 ELECTRIC WIRING. of a single group of cells. In Pig. 3 is shown six voltaic cells connected in multiple-series. Q. Is it necessary to connect all electric gen- erators and devices in the same way in order to produce similar results? A. Yes; and the following rules apply to all de- vices alike, viz.: (1) Connecting devices in series adds their indi- vidual E. M. P. and resistance. (2) Connecting devices in parallel joins their indi- vidual current capacities. The total resistance is equal to the resistance of one device divided by the number of them. (3) In multiple-series groups, each sub-group of devices in series is considered a unit member with reference to the entire group. Q. Do these rules apply to secondary or storage cells, the same as to primary or the ordinary vol- taic cells? A. Tes; to electrical devices of every descrip- tion. F.g. 3. Cells in Multiple Series. EhECTKlC WIRING. 23 SERIES CIRCUITS. Q. "What is a series circuit? A. In a series circuit one or more electric sources such as dynamos are so connected with a number of electro-receptive devices, such as lamps, that the current passes successively through each of these devices from the first device to the last. In Fig. 4 is shown seven lamps connected in series. Q. What is a multiple or parallel circuit? A. In a multiple or parallel circuit a number of separate electric sources, such as dynamos or sep- arate electro-receptive devices, such as lamps, or both, have all their positive poles connected to a single positive conductor, and all their negative poles similarly connected to a single negative con- ductor. In Fig. 5 is shown four lamps connected in parallel or multiple circuit. Q. Does a series circuit, and a multiple or paral- lel circuit require the same character of current to be supplied to the electro-receptive devices? A. No ; a series circuit requires a constant cur- rent, while a multiple or parallel circuit requires a constant potential or electro-motive force- It is, therefore, for this reason that a series circuit is called a constant current circuit, and a multiple or parallel circuit is called a constant-potential cir- cuit. "~ Q. "What determines the kind of circuit to be used? A. The character of the electro-receptive devices 24 ELECTRIC "WIRING. to be supplied by the circuit. For instance, are lamps are used on a series circuit, while incandes- cent lamps are used on a multiple or parallel cir- cuit. With arc lamps a constant current is required, while with incandescent lamps a constant potential is required, as will be herafter explained. Q. How is a voltmeter connected in a circuit? A. As this instrument is used to measure the potential difference between any two points in a circuit, it is therefore connected across the circuit, that is, it is connected in parallel or shunt. Q. How is an ammeter connected in a circuit? A. This instrument is used to measure the vol- ume or amount of current passing through a cir- cuit. It is, therefore, connected in the circuit in series. In Fig. 6 is shown the connections both of an ammeter and of a voltmeter. Q. How is the voltage and amperage of different circuits kept constant? A. By the coupling of the two or more (sources) generators in certain definite ways. For instance, in coupling two or more generators in parallel the pressure or voltage of the machine is kept constant, while the current or amperage alone varies. On the contrary, by coupling these machines in series. the pressure or voltage of the machine varies, while the current, or amperage, remains the same. "When the machines are connected in parallel all the posi- tive terminals are connected together, and all the negative terminals in the same way; or, for con- ELECTRIC WIRING. 25 s o o O Fig. 6. Comeetions of Ammeter and Votmeter. 26 ELECTRIC WIEING. venience, the positive and negative terminals of each machine can be respectively connected to two insulated copper bars, called omnibus or bussbars. When the machines are connected in series, the negative and positive terminals are connected to each other. CONNECTING MACHINES IN SERIES. In Pig. 7 is shown shunt dynamos in series. In Pig. 8 is shown series dynamos in series. Connecting machines together in series or in par- allel can be compared to the harnessing of horses in tandem or abreast. When electrical machines (generators) are con- nected in series the machines are then like horses harnessed in tandem, that is, one before the other; and when the machines are connected in parallel, they are then like horses harnessed abreast, that is, side by side. Q. Is the output or power (watts) of the machines affected by the method of their connection? A. No; power (watts) is the product of volts Xamperes, and we have seen that connecting elec- trical devices in series increases the voltage, but the amperage remains the same ; while connecting de- vices in parallel increases the amperage, the volt- age remaining the same. In the same way the work done by horses is prac- tically the same, whether they are harnessed tandem or abreast. The method of connecting electrical devices, or horses depends upon the character of work to be done. ELECTEIC WIRING. 27 CD m PI 6D 28 ELECTRIC WIRING. 02 d •l-H a as 60 ELECTRIC WIRING. 29 CONNECTING MACHINES IN PARALLEL. In Pig. 9 is shown shunt machines in parallel. In Fig. 10, series machines in parallel. In Fig. 11, compound machines in parallel. Q. Why is it necessary to connect the machines together in these different ways? A. The output of every electric generator con- sists of two factors, the pressure or voltage, and the currents or amperage. The uses of electricity at the present time require the maintenance of either a constant current, or a constant pressure in a circuit ; and, to comply with these requirements it becomes necessary to connect the machines to- gether in some one of the above different ways, depending upon the character or the electro-recept- ive devices to be supplied. Q. For what work are these different types of machines most used? A. The series wound machines supplying a con- stant current, are used almost exclusively for street car motors. The shunt and compound wound ma- chines, which give a constant potential or voltage, are practically used for all power and incandescent lighting circuits. We, therefore, see that the con- stant current type is devoted almost exclusively to arc light, and street car motors, while the constant potential or voltage type are used almost exclu- sively for power and incandescent lighting circuits. The compound-wound machine, giving a constant potential, is by far the most used, owing to its 30 ELECTRIC WIRING. BUS BARS Fig. 9. Shunt Machines in Parallel. ELECTRIC WIRING. 31 OS a o 32 ELECTRIC WIRING. ^j1 "NM eCiTtO «Ca09 MtC' loijjo SaS jsd spuiio^ t: noi9l M^^ m»' g^!3 =5 iaa Gpiiito, ii?LJil_II2IHi: KnN oif* 5RS Ko£> SaBiS Ow s?ss 7. .g8 31.81 45 238. 22.22 ?■??' 24 93 131 05 •;o 11 ?'?§i 19 77 ll)t.40 50 58 30 158. 33.33 ^m 1.-. m fi2.792 63.78 4,086 12.44 05 058 80.42 20 106. 5000 3,249 9 85 02 069 101 40 2,601 7 82 41.292 127 87 14 . 74. 7140 5'S^ 6.20 32.746 101 34 1.600 4.92 , 25.970 203.31 10 53. 100 00 }S 3.00 20. .594 260 39 1,024 3.09 16.331 323.32 Table. 5 EesistHate of Copper Wire. Table No. 5a. Weight of Copper Wire. ELECTRIC WIRING. 71 Q. What is a convenient way to get an approxi- mate idea of the size of any copper wire? A. The resistance of 1000 feet of copper wire one- tenth of an inch in diameter is equal to one ohm. Q. What size wire has this resistance? A. A No. 10 wire (B. & S. gage). Q. Give a convenient formula for finding the number of circular mils where the current in am- peres and the distance in feet is known. CXDX21 A. C. M.^ in which formula C= Loss, current, and D=distance in feet. Q. Give a convenient wiring table for daily use. A. See Table No. 6. Q. Give a table showing the volts lost at different per cent, drop? A. Table No. 7, on page 73 is a convenient table to use for finding the drop. 72 ELECTRIC WIRING. WEIGHT PER AREA SAFE B. &6. 1000 FT. LBS. IN CURRENT GUAQE TRIPLE BRD. CIRCULAR M(LLS IN INSULATION BARE WIRE AMPERES 0000 742 211600. 312. 000 609 167805. 262. 00 487 133079.4 220. 386 105538. 185. 1 303 83694.2 156. 2 244 66373. 131. 8 194 52634. 110. 4 160 41742. 92. 5 184 83102. 77.6 6 111 26250.5 65.2 7 20816. 548 8 ""73 16509. 46.1 e 13094. 38.7 10 "50 10381. 32.5 11 8234. 27.3 12 "8~6 6529,9 23. 13 _ 5178.4 19.8 14 26 4106.7 16. 15 8256.7 13. 16 21 2582.9 8. 17 2048.2 6, 18 '15' 1624.3 5 Table 6. Wiring Table for Daily Use. s c* 8 ELECTRIC AVIRING. ^s l>t^OU20D^-(t^O!Dt--h-Oi0C00i00l>'-'OOQ0 r-( iX) iS 05 N ■— CO O CO C-1 t-_ 05 t> CO CO 05 --H -^ l> O Ol "SS K "5 S ^ '^ <5i t* C^ C^ 05 O CO ■* O 03 « ■* MOM rH cq "y' W CD CO o >-(' lo o > o -^' t^' ■** ^' OS 00 cd co o" wr* •-05^HTT*CSi03<-H'eT.C5(NlLQOOlCCO CO— (iCiO-MCJO'TCO^OiCOiCMLraoCDr^'MOCD ira .-H 1-- -51 (M_ O 03 OO 05 (M_ 00 CD 1-- (N Oi_5 « O "-< O CO lO >-H CD fiii od T(i OS id t*' o" N i6 Qo' (N tc'o ■^" ca -t^' > o cd" ^^wt^(^Icoeo■^^^l"-ooo^oc^^colocob-Oi^-cD '-ti-l'-H|-Hi-li-(t-H(MCO |> lO CO N "-H O 05 Oi O: rH -^ CO tH r-< Oi O ^ ii^ 0'iS_ CO N* u3 oo'^-1' TfT I—' as (N oo' ic ^ t-' ^* •-* r-' lo w os i-^ r-' vi «-li-ii-li-ICQ000O5CO00 3COCDO"*OOCOOOCOOSIO»- CO.-100'*«OOSQOOie' oo' OS o cC0l>Oe0TH0SC0l000THcCU5Or* WOtO'-HCOC^t-CO'J^C^OOOfMlOQOrHlCOSCOOCD CDcqOSOCOCDOOf-(l>CCOSlO ^. "^ '■'". ^ r-t* ^' rH (M' in' CO CO' th' lO ifii CD J>' t> OO' Os' CO r-.' ^ii> lO Ifl lO ' ^' rH N M CO CO '*' id X" t> GO 05 O' rH N «J TtJ id o gj >- 74 ELECTRIC WIRING. CHAPTER V. Elements of a Wiring System. Q. "What are known as the elements of a wiring system ? A. The mains, the feeders and the branches. In Fig. 27 is shown these elements. Q. Which of these constitute the trunk of the system ? A. The mains and the feeders, since through these the current is fed to the various branch cir- cuits. Q. Is the main or the feeder the principal con- ductor ? A. The feeder, since it distributes the curernt throughout the system. The term feeder also often refers to a conductor which begins at the switch- board, or at the service supply, and terminates at Coils With and Without Core. ELECTRIC WIRING. 75 FEEDER BRANCH C_ fF=^ V^ -=F^ Pig. 27. Mains, Feeders and Branches. 76 ELECTRIC WIRING. the center of distribution of the system. From this center of distribution, mains are employed to distribute the current to the branch circuits. Q. AYhat is the difference between a lead and a feeder? A. A lead is an insulated conductor leading to or from an electric source, usually from the machine to the bus bars. Q. Are the feeders, or the mains, connected to the bus bars for the outgoing current? A. The feeders, though these conductors are sometimes called the mains. Q. What, then, would you call a prolongation of a feeder? A. A main. Q. In laying out a wiring system, must all these elements be considered? A. Yes; and especial attention must be given to them. Q. Suppose we had a total drop of 9 volts, how much must we allow for each of these elements? A. Three volts to each element. Q. In laying out a wiring system, what is the chief item of expense? A. The labor to install same. Q. Is this more important than the cost of cop- per? A. Yes ; and for this reason every wiring sys- tem must first be carefully thought over, and then ELECTEIC WIRING. 77 clearly mapped out. Experience is the best of all teachers, especially in electric wiring. Q. In addition to the three elements above named, what other wires are often referred to as an element? A. The wires rising through a building from floor to floor, called "risers." Proportioning^ the Drop in the System. Q. In laying out a wiring system, what is one of the most important features to be considered? A. The selection of the center, or centers, of distribution. Q. How must the centers of distribution of a wiring system be selected? A. With the view of a uniform distribution of the current and the pressure to the lamps or outlets utilizing same. Q. Give an illustration of the advantage of a proper selection of a center of distribution. A. We have a lino 2000 ft. long consisting of No. 10 wire, carrying 20 lamps at each end of the line, on a llD-volt circuit, how should the current be fed to the line so as to keep the drop at a mini- mum? A. If the current is supplied from one end of the line, then the drop would be (D=C X R)= current of the 40 lamps X resistance of 4000 ft. No. 10 wire=20 X 4=80 volts. Therefore, the lamps nearest to the point at which the cur- rent enters the line would receive 110 volts minus 78 ELECTRIC WIRING- 20 volts, or 90 volts; while the lamps at the other end of the line, 2000 ft. away, would receive only 90 volts, minus 20 volts, or 70 volts. Q. "Would it be practical, then, to locate the center of distribution at the end of the line? A. No; such a large drop as the above would be too heavy a reduction of the candle power of the lamps- Q. Suppose we make the center of distribution at the middle of the line, instead of at the end, what then would be the result? A. The current would then have to travel only 1000 ft. to each end of the line, instead of 2,000 ft. as before. The drop would therefore be (D = CXR)^current of 20 lamps X resistance of 2000 ft. of No. 10 wire=10x2=20 volts drop, instead of a 40-volt drop, as in above illustration. This would, therefore, make a much more uniform dis- tribution of pressure for the lamps. Q. How could we still further reduce the drop in this circuit? A. If, instead of feeding into the end or the middle of the circuit, we run two feeders, each 500 ft. from the end, we would then have for the drop (D = C X R)=current of 20 lamps X resistance of 1000 ft. wire=10 amperes X 1 ohm ^ 10 volts drop. We have therefore the following results : Locating center of distribution at end of line, drop 80 volts. ELECTRIC WIRING. 79 Locating at middle of line, drop 20 volts. Using two feeders, drop 10 volts. From these illustrations it can be seen how greatly the point or points from which the current is distributed eifeets the drop in voltage, and hence the efficiency of the lamps. Q. Do the above illustrations apply to circuits other than lamp cir''-uits? A- Yes ; to all kii:ds of wiring cirepi-ts, includ- ing street railway work. Q. Explain how electric ears are operated on a wiring system similar to a lamp circuit. A. The trolley wire is one leg of the circuit, and the tracks the other leg, the one corresponding to the positive wire and the other to the negative wire of an ordinary circuit. Between these two conductors the ears are operated, as shown in Fig. 28. Therefore, the ears take the place of lamps in an ordinary lamp circuit. The current which the ears take is the course of a heavy drop in the line voltage. To reduce this as much as possible instead of feeding the current from the end or the middle of the line, it is fed into the line at various points where most needed, as shown in Fig. 28. Sometimes these feeders are every 100 ft., and by this means a comparatively uniform pressure is maintained throughout the en- tire line under all conditions of the load. Equalizing the Pressure. Q. How have we seen the pressure of a wiring 80 ELECTRIC WIRING. a o t3 fe CO ELECTEIC WIRING. 81 rystem is equalized? A. By the proper location of the centei's of dis- tribution of the circuit. Q. Is there usually more than one center of dis- tribution in a wiring system for the distribution of the current? A. Yes; in apartment houses and hotels, and in any place where it is absolutely necesary that there shall be no variation in the lamps, it is necessary to use several centers of distribution, sometimes as many as a half-dozen such centers. In Fig. 29 is shown one center of distribution, and in Fig. 30 two centers of distribution of an ordinary lamp circuit. Q. Give an ordinary wiring diagram such as used in every day work, showing the drop limited to four volts. A. In Fig. 31 is given such a diagram- The drop from the dynamo to any group of lamps does not exceed 4 volts. This can be seen by tracing the circuit from the switch to each group of lamps. Q. How also is the voltage of a wiring circuit kept uniform? A. By using a dynamo which will permit of close regulation. Q. What class of dynamo is used for this pur- pose? A. Shunt wound and compound wound dynamos. Q. What is the chief difference between these two machines? 82 ELECTRIC WIRING. P □ P i^ o M a Fig. 29. Lamp Circuit with One Center of Distribution. Fig. 30. Lamp Circuit with Two Centers of Distribution. ELECTRIC WIRING. 83 A. The voltage of the shunt machine is regulated through the fields by hand, while the compound machine is entirely automatic in its operation. It is for this reason that the compound machine is more generally used. Q. G-ive the formula for calculating the B. M- F. of a dynamo? A. The electromotive force is equal to the revo- lutions of the armature per second X number of conductors on the armature X the number of lines of force passing through the armataure; or, as it NXCXn, is usually expressed, E = , in which f orm- 100 million ula N = line of force, C = conductors and n = speed per second in revolutions. The 100 million is the number of magnetic lines of force, which must be cut by the conductors per second to produce one volt. Q. What three things are always necessary to produce electro-motive force? A- Motion, magnetism and conductors. Q. How can the electro-motive force (voltage) be regulated? A. It may be increased or diminished in three ways, viz. : (1) By increasing or diminishing the number of conductors on the armature ; (2) By increasing or diminishing the strength of the fields; and, 84 ELECTRIC WIRING. Fig. 31. Wiring Diagram Limiting Drop to 4 Volts. ELECTEIC WIRING. 85 (3) By increasing or diminishing the revolutions per second. Q. Which of these methods is generally em- ployed? A. The second, the lines of force being increased or decreased in the fields. Q. How is this done in a shunt machine? A. By means of a resistance box connected in circuit with the winding of the magnets (fields). By turning the handle of this box, the current is increased or decreased as the power of the magnets is increased or decreased. If the dynamo must develop more pressure, the magnets are made to develop more magnetism (lines of force) by in- creasing the current passing through them. This is done by varying the resistance by means of the resistance box or rheostat, as it is usually called. Q. In order to produce 110 volts, how many lines of force would have to be cut, the machine having a speed of 100 revolutions per second with 110 conductors on the armature? A. There would have to be cut one million lines of force per second- Q. In order to produce one extra volt, making a total of 111 volts, how many lines of force would have to be cut? A. Only one million divided by 110, or 9.091 lines of force, since every time each one of the 110 conductors cuts the one million lines of force, it produces one volt. 86 ELECTRIC WIRING. Q. With a machine running at a speed of 100 revolutions per second, with one conductor, and a field strength of one million lines of force, what voltage is produced? A. One volt, because the one conductor cuts the one million lines of force 100 times per second, and we have seen to produce one volt, 100,000,000 lines of force must be cut per second. Q. With such a machine producing an E. M. F. of 110 volts, will it necessarily send out over tho lilies this much pressure? A. No ; on account of the drop in the armature conductors. As the load increases the drop in these conductors also increases, so that if some means were not pro- vided to increase the strength of the fields as the drop increased, the dynamo would be a very im- perfect machine. Again, the armature itself is an electro-magnet, and, as the current increases the magnetic strength of these conductors increases, but its action is opposed to the magnetic action of the fields, so that if some means were not provided to overcome this, the machine would finally become inoperative as the load increased. Q. How are these obstacles overcome in shunt wound machines? A. By means of the rheostat, which must be constantly regulated should there be rapid changes in the load. By this means both the armature drop and the magnetic armature re-action, is overcome. ELECTRIC WIRING. 87 Q. Is this constant regulation by hand not very inconvenient? A. Yes; and for this reason the shunt wound machine has been almost entirely replaced for in- candescent lighting by compound wound machines which regulate the fields automatically.. This ma- chine automatically increases the strength of its fields, without the aid of a resistance box, so that both the armature drop and the armature re-action of the machine is fully compensated or overcome. Q. How is this done? A. Without entering into the construction of the machine, as only the armature forms part of any wiring system, it is sufficient to say that the above regulation is accomplished by sending the main current around the field coils, so that as the cur- rent varies the strength of the fields vary ; therefore the machine will produce more volts only when the armature produces more current. Q. Why is it necessary that the field strength be increased with the load? A. To increase the E. M. F. generated in the armature, and in this way compensate for the loss or drop in the armature circuit. It is for this pur- pose that the field magnets are compound wound, the series coils being used to compensate for the drop in the armature and the external circuit. Q. What is meant by over-compounding a gen- erator ? A. It is such a compounding of an electric ma- 88 ELECTRIC WIRING. chine as produces under an increase of load an increase of voltage at its terminals. This effect is produced by placing a sufficient number of turns on the series coils so as to increase the difference of potential between the terminals of the machine above normal as the load increases. Q. Give an illustration of the operation of an over-compounded generator. A. An ordinary over-compounded 110-volt gen- erator will produce about 116 volts at one-quarter load, 111 volts at one-half load and 112 volts at full load. Q. Why is it so essential to have a constant po- tential system for incandescent lighting? A. Because incandescent lamps are manufac- tured to give a certain candle power with a certain terminal pressure, usually 110 volts. If the pres- sure becomes too great, the filament becomes over- heated and the lamp burns out. If too little, the lamp does not burn at its full capacity, and there is a waste of current. Most incandescent lamps are manufactured for 110-volt circuits, and with this pressure kept constant the effective life of the lamp should be about 700 hours. ELECTRIC WIRING. 89 CHAPTER 6. Systems of Wiring. Q. In what two ways is electricity distributed? A. By a constant potential (voltage) current; or by a constant (amperage) current. Magnetic Circuit. 90 ELECTRIC WIRING. Q. In wiring calculations which of these two cur- rents are mostly used? A. Constant potential currents. Q. In what electric work is constant potential currents used? A- In incandescent lighting, and a great deal in modern arc lighting; also in street railway work, and all long distance transmission work. Q. "What two systems of connecting lamps and generators are mostly used? A. The series and the multiple arc systems. Q. "Which of these two systems is most generally used for lighting and power purposes? A. The multiple arc system. Q. Describe this system. A. The two wires run side by side, the one the negative and the other the positive, and the lamp or motors are connected across from one wire to the other wire, as shown in Fig. 32. As in this system a constant difference of pressure is main- tained between the two wires or sides, it is known as a constant potential system. Q. Does the amount of current also remain the same ? A. No ; the current or number of amperes varies in proportion to the lamps or motors carried by it. Q. "What system is used almost exclusively for series arc lamps? A- The series system. The wiring of this system is in the nature of a loop, the greatest difference ELECTEIC WIRING Pig. 32. Multiple Are System. — Incandescent Lamps. Fig. 34. Series System. — Incandescent Lamps. 92 ELECTRIC WIRING. of potential being at the terminals of the loop. In Fig. 33 is shown 7 arc lamps connected in series by this method of wiring. In Fig. 34 is shown 3 incandescent lamps connected in series on constant potential mains. Edison Three- Wire System. Q. Explain the Edison three wire system. A. The object of this system is to permit the use of increased pressure without increasing the voltage of the lamps. As incandescent lamps are not manu- factured to stand a pressure of more than 110 volts, this system was devised in order to permit their use on a 220 to 250 volt circuit. In Fig. 35 is shown this method of wiring. The third wire is a neutral wire which keeps the system in balance. The dynamos or generators are connected in se- ries, that is, the positive of one is connected to the negative of the other. Each machine generates 110 volts, making 220 volts generated, but the surplus over 110 volts flows back to the machines over the neutral wire, so that each lamp never takes over 110 volts. This method of wiring is extensively used for all kinds of electrical work. Wiring for Three Wire System. Q. Can a three wire system be used on any other system than a constant potential system? A. No. Q. Describe the wiring for the three wire system. ELECTRIC WIRING. 93 Pig. 35. Edison Three-Wire System. 94 ELECTRIC WIRING. A. It consists of three main wires which start from the generating plant and ramify everywhere through the district or building to be lighted. The dynamos or generators are arranged in groups of two. One lateral lead starts from the negative binding post of one dynamo. The positive termi- nal of this dynamo is connected to the negative terminal of the other dynamo. Between the two dynamos the central or neutral lead or wire is con- nected. The other lateral lead or main starts from the positive binding post of the second dynamo. The lamps, motors, or other appliances to be oper- ated by this system, are calculated for the potential difference of a single dynamo, which is usually 110 volts. The appliances to be operated are ar- ranged between the neutral wire and the two later- als, care being taken to give as even a disposition of same as possible. If evenly arranged and all the lamps or motors in operation, no current passes through the neutral wire. If only the lamps situ- ated on one of the circuits or lateral mains are lighted, then all the current goes through the neu- tral wire. In all other eases, the neutral wire re- ceives only the excess of current. Q. If lamps of double the present standard of 110 volts were used, would there be any economy in the use of the three wire system? A- No ; as there would be no necessity for using this system of wiring. Q. Could not the lamps or motors be connected ELECTRIC WIRING. 95 in groups of two in series between the outside mains, and in this way dispense with the third wire, as the voltage of the two lamps in series would then be 220 volts? A. Yes; but the lamps or motors would have to be operated in pairs; the lamps being lighted or extinguished in pairs, otherwise their voltage would not be adapted to that of the system (220 volts). Q. How does a third wire avoid this? A. By taking care of any difference in the volt- age. Q. What regulates the division of the current between the laterals and the neutral? A. The resistance of the load. As the voltage between the two laterals and the neutral is kept con- stant, the amount of current flowing between either lateral and the neutral is determined by the resist- ance (load) between the lateral and the neutral, regardless of what exists between the other lateral and neutral. Therefore, the difference between the current on one side and the current on the other side, is equal to the current carried by the neutral wire. Example. Q. We have one generator supplying five lamps on lateral main A and the other generator supplying ten lamps on lateral main B, assuming each lamp carries one-half ampere; how much current is the neutral wire carrying? 96 ELECTRIC WIRING. A. Main A carries 2% amperes, and main B carries 5 amperes, so the neutral would carry 2^/2 amperes. A current of 2% amperes would flow through the main A and unite with the current of 2% amperes flowing through the neutral, and the united current carrying 5 amperes would then flow through main B back to the generator- Q. Suppose we cut the neutral wire, what would take place? A. The current of 5 amperes would try to flow through the main A and the 5 lamps, which lamps can carry only 2V2 amperes, and hence would de- stroy them. Q. Suppose we had a 220 volt motor to operate on this system, would it be necessary to use the neutral wire? A. No; it should be connected direct across the two mains which we have seen carry 220 volts, as shown in Fig. 36. Q. If the lamps were always kept lighted in even numl)ors on each side of the neutral wire, could the neutral wire be dispensed with? A. Yes; though, as already seen, the lamps would have to be operated in couples. Size of Wire in Three Wire System. Q. Upon what does the size of the neutral wire chiefly depend? A. Upon whether the system is for interior house work; or, exterior district work. Most interior ELECTRIC WIRING. 97 lEO VOCTJj. (^ ® Fig. 36. 220-Volt Motor on Three-Wire System. 98 ELECTRIC WIRING. work is two-wire work, connecting with an out- side three-wire system. Where the three-wire system is used for interior work, the neutral wire is usually made the same size as the lateral mains, so that should one of the outer fuses blow, the neutral wire could carry the same current as the outer wire. The cross-section of the neutral wire is often made equal to the combined cross-sec- tions of the two outer wires, thus permitting the system to be easily changed over to a two-wire system. This permits the three-wire system to be operated as a two wire system, and, in case of emer- gency, to connect with an outside three-wire system. For outside or district systems, the neutral wire is usually made one-half the size. .of the lateral mains- Q. What saving in copper is made in the lateral mains of a three-wire system over that of a two- wire system? A. The circuit of a three-wire system has the two outer mains maintained at double the potential difference as that which is required in a two-wire system, carrying the same number of lamps, hence the current carried is only one-half that which would be required in a two- wire system ; and, there- fore, the mains can be made one-half as large, thus making a saving of one-half in copper. This does not represent the actual saving in copper, as the neutral wire must be added to this. Q. If the system balanced, does any current flow in the neutral wire? ELECTRIC WIRL\G. 99 A. No; and hence in a well-balanced system the neutral wire can be with safety made smaller then the lateral mains. Q. If all the lamps on one side were lighted and none on the other side, how much of the current would the neutral wire take? A. The same as one main or side, which would be the entire voltage of one machine, usually 120 volts. Q. Suppose a fuse blew out on one side or main, what would happen? A. The lamps on that side would be extinguished, as there would be no current on that side. In this event, the neutral wire would take the entire cur- rent of the other side the same as though it were a two-wire system. Q. Is it always necessary to place a fuse in the neutral wire? A. Yes; except when a grounded neutral has the same cross-section as either of the outer wires. Q. Does the neutral wire ever have two currents going through parts of it in opposite directions? A. Yes ; in order to keep the system balanced this often happens, a portion of the neutral wire in this case taking no current. Q. Is the three-wire system also used with alter- nating currents? ' A. Yes; provided it is a single-voltage system. Q. Is the size of wire used effected by the char- acter of the current? 100 ELECTRIC WIRING. A. No ; that is, not for ordinary work. CODE REQUIREMENTS. Direct Current 3 Wire Systems. a. Neutral wire may be grounded and when grounded the following rules nLust be complied with : — 1. Must be grounded at the Central Station on a metal plate buried in coke beneath permanent moisture level, and also, through all available un- derground water and gas pipe systems. 2. In underground systems the neutral wire must also be grounded at each distributing box through the box. 3. In underground systems the neutral wire must be grounded every 500 feet. ELECTKIC WIRING. 101 CHAPTER 7. Methods of Wiring. Q. What methods of wiring are now approved by the National Electric Code? A. Those using: (1) Rigid conduits; (2) Flexible conduits; (3) Armored cables; (4) Flexible tubing; (5) Knob and tube work; (6) Cleats or insulators; (7) Moulding. Q. Into what two general classes can all electric wiring be divided? A. Into (1) Concealed Wiring and (2) Exposed Wiring. Magnetic Whirl Around Wire. 102 ELECTRIC WIRING. Q. What is meant by concealed wiring? A. Interior wiring placed out of sight, being either built in the plaster of a room or carried through suitable conduits placed therein- Q. What do you mean by a conduit? A. A space employed for the reception of elec- tric wires or cables. Conduits are usually employed in underground work. All wires for use in conduits must have an ap- proved rubber insulating cover. Q. What is meant by exposed wiring? A. Wiring outside of buildings. Q. "WTiat methods of wiring are used for con- cealed wiring? A. Rigid Conduits, Flexible Conduits, Armored Cables, Flexible Tubing, and Knob and Tube Work. Q. What methods of wiring are used for ex- posed wiring? A. Rigid conductors, Cleat or Insulators and Moulding. Q. Rigid conduits are then used for both interior and exposed wiring? A. Yes; but generally for exposed wiring. Q. What are the requirements of a good conduit? A. First, it must be fire-proof; second, moisture proof, and, third, mechanically strong. While there are other requirements these three are the principal ones, and by far the most important. Q. Why should the conduit be built so as to be fire-proof? ELECTRIC WIRING. 103 A. Because there exists in every electric circuit for lighting or power the elements which usually produce combustion. For this reason the conduits are usually metal pipes of the thickness of ordinary gas pipes. Q. "Why should they be moisture proof? A. To protect the insulated wires which are carried within the conduits from dampness, which would damage and soon rot the insulating ma- terial required to protect the wires. The damp- ness would also damage the insulating lining of the conduit itself, where such lining is used. Q. Why should the conduits be mechanically strong 1 A. To resist any nails that might be driven into them; and also the hard blows they are apt to re- ceive before and while being installed. Q. How may rigid conduits be divided? A. Into two classes, viz: (1) Conduits with lin- ing of insulated material, and (2) Unlined conduits, which, however, have an inner coat of enamel, or some similar material. Q. Describe a lined conduit. A. It usually consists of a plain iron pipe lined with a tube of paper which has been treated with an asphaltic compound. The pipe is then coated inside with an enamel. Sometimes the pipe is, also, enameled on the outside, I)ut usually is only galvanized. Q. Describe an unlined condiiit. 104 ELECTRIC WIRING. A. It consists of an iron or steel pipe, similar to a gas pipe, which is coated inside with enamel. It usually is galvanized on the outside, but is some- times also enameled. Q. What are the advantages and disadvantages of an unlined conduit? A. Its advantages are (1) its cheapness; (2) the ease with which it can be installed, as it can be easily threaded and bent; and, (3) the ease with which the wires can be inserted or withdrawn, ow- ing to its interior being enameled, and, therefore, smooth. Its principal disadvantage is the requirement of the National Electric Code that all conductors placed therein must be double braided, -which in- increases to a slight expense the cost of the con- ductors- Q. Is double braided conductors required in lined conductors? A. No; only single braided conductors. Should an unlined conduit break, through corrosion or otherwise, then the conductors would be exposed, which would not be the case in a lined conduit, as they would still be protected to a great extent by the insulated lining of the conduit. Q. For what character of work are unlined con- duits generally used? A. For all buildings or places where the conduit is not liable to corrosion. Its use is increasing very fast owing to the introduction of double braided ELECTRIC WIRING. 105 conductors, and the use of insulating bushings at the terminals of all conduits, which prevent the conductors from resting on the bare pipe. Flexible Conduits. Q. What is the advantage of a flexible conduit? A. It permits the conductors or cables to be in- troduced at any time after its completion. Q. How is a flexible conduit constructed? A. It consists of a continuous flexible steel tube, composed of convex and concave metal strips, which are wound spirally upon each other, so as to interlock their concave surfaces, both inside and outside. In this way is secured a smooth and al- most frictionless surface both inside and outside the tube, and, thereby, permitting the conductors to be inserted in same with ease- In Fig. 37 is shown a flexible conduit. Q. Is this conduit also fire-proof, the same as the rigid conduit? A. Yes ; it is so considered, and its use is per- mitted by the Code in fire-proof buildings. Q. What are the advantages claimed for flexible conduits ? A. Their flexibility, ventilation and mechanical strength. Their construction also permits them to be made in great lengths, even in coils of from 50 to 300 feet, depending on the diameter of the con- duit. This avoids joints, couplings, etc., and permit:? of quick installation. Its flexibility and continuity 106 ELECTRIC WIRING. Fig. 37. A Flexible Steel Armor Conductor. Fig. 38. An Armored Cable. ELECTRIC WIRING. 107 also permits it to be used in completed buildings, ^vithout disturbing floors, ceilings or walls, by "fish- ing" it between the ceiling beams and flooring. Q. What precaution must be used in "fishing" the tube where there are any bends? A. The tube must be securely fastened in at least two points at the elbow to prevent the tube from buckling- Armored Cable. Q. How are armored cables constructed? A. In a very similar manner to flexible conduits with the exception that the conduit is made over the conductors. In Pig. 38 is shown an armored cable. Q. What advantage has it over flexible con- duits? A. It is much more easily installed since the coinplete armared cables are driven through the spaces between the walls, floors and ceiling ; while, with the flexible conduits the conductors must be drawn through the flexible conduits after the con- duits have been installed. The diameter of the armored cables are smaller than the corresponding flexible conduits which permits them to be drawn through smaller spaces. Flexible Tubing. Q. Describe flexible tubing. A. In Fig. 39 is shown a piece of flexible tubing. i08 ELECTRIC AVIEIXG. bci E ELECTRIC WIRING. '109 nor mechanically strong, its use is only permitted by the Code in non-fire-proof buildings- Knob and Tube Work. Q. Where is this method of wiring used? A. Only for wiring frame structures when the first cost is of the greatest importance. The wires are run concealed under floors, and supported on porcelain knobs. Where the wires pass through floors and beams they are insulated by porcelain tubes, such as shown in Fig. 40. Q. Is this a safe method of wiring? A. No; since the wires are not only subject to mechanical injury, but are also subject to inter- ference and injury from rats, etc. As the sag in the wires is liable to bring them in contact with beams, lathes, etc., a fire would prob- ably result, should the wires become overheated, or a short circuit occur. Q. How are the knobs constructed? A. In two forms, (1) the solid knob, and (2) the split knob. With the solid knob, the conductors are secured on same by means of tie wires ; while with the split knob the conductor is held in position between the portions of the knob. The cost of the two forms of knobs is about the same. Cleats or Insulators. Q. In what work is this method of wiring used? A. In all exposed work, usually in mills, fac- tories and for heavy mains. 110 ELECTRIC AYIRIXG. In Fig. 41 is shown samples of cleats. In Fig. 42 is shown this method of wiring. Q. Are the wires used in this method required to be rubber covered? A. No ; the ■ use of slow burning weather-proof wire is permitted by the Code in this class of wiring. Q. In passing through floors, partitions and walls, how must the conductors be protected? A. By means of porcelain tubes and bushings, and sometimes by the use of iron pipes. Q. Where should knobs be used instead of cleats? A. For voltages over 300, and in damp places, as the Code requires in such cases that the wires be held at a distance of not less than one inch from the surface wired over- Q. Where there are a number of heavy feeders, what form of insulators should be used? A. The rack type. Q. Of what does this consist? A. It consists of a frame or rack as shown in Fig*. 44. In this rack are placed the insulators to be used. These insulators are usually heavy, stout porcelain blocks with an opening through their center, and through this opening the conductors are passed. In Fig. 45 is shown such a porcelain insulator- The insulator is split so that it can easily be re- placed in case of breakage. This, also, permits the conductor to be placed in the insulator without ELECTEIC WIRING. Ill ; ; Fig. 40. Insulating Porcelain Tube . Fig. 41. Porcelain Cleats. 112 ELECTRIC WIRING. being drawn through it, and thereby injuring the insulating cover of same. Q. How are the insulators placed in the frame? A. As seen in Pig. 14 the rack consists of an angle or T iron, to which are secured straps of iron projecting outwardly- The slots in the in- sulators fit over these strips, and in this way they are held in place. On the outer side of the rack there are separate straps, which further serve to secure the insulators in place and at the same time serve to stiffen the rack. Q. flow are these racks secured to a brick wall or ceiling? A. By toggles, expansion bolts or similar devices. Wooden pegs must never be used, as these plugs soon get loose and pull out, even where the best seasoned wood is used. Moulding. Q. Explain the difference between open work and exposed work. A. In open work the insulated wires are in plain sight, being supported by knobs or cleats. In exposed work, the wires may be out of sight, but the moulding or conduit in which the wires are run is exposed. Q. Conduits then may be used for either open, exposed or concealed work? A. Yes; but moulding can only be used for ex- posed work. ELECTRIC WIRING. 113 Fig. 42. Cable Cleat Carrying Wires. 114 ELECTRIC WIRING. Q. Where is moulding principally used? A. In making circuit extensions in completed buildings, such as extending circuits in offices, stores, etc. Q- Is moulding never used in new work? A. Only where the use of cleat work would be objectionable from the standpoint of appearance. Q. What precaution is necessary in the use of moulding 1 A. It must never be used in any place where there is dampness. . For this reason moulding should never be used in cellars, laundries, or attached to brick walls or elevator shafts. Q. What two kinds of moulding are in present use ? A. Wooden- and metal moulding. Q. Where only can eith&r of these two kinds of moulding beT used?' ," - -. ' i A. Where .there is no .concealed system; and, where the ap]>earance of open knob or cleat work prohibit their use, such as in residence, etc. Q. How is wooden moulding made? A. It is made in two parts, a backing and a cap- ping. In Fig. 46 is shown its construction, and in Fig. 47 is shown the minimum dimensions allowed by the Code. Both soft and hard wood are used in their construction, though hard wood is the better as it is stronger and does not absorb moisture. In order to prevent the absorption of moisture as much as possible the moulding must be coated with ELECTRIC WIRING. 115 D~ i Ol o: o I o Fig. 44. Wiring Racl:. Fig. 45. Insulator for Rack. 116 ELECTRIC WIEING. a waterproof material. Two coats of shellac is generally used for this purpose. Q. What insulation for the wire is used with wooden moulding? A. Single braid rubber covered wire, since the wires are in direct contact with the wood ; and only separated from each other by the tongue of the moulding. Q. How is wooden moulding put up? A. The backing is first screwed to the wall or ceiling, and the wires are then laid in the grooves, the capping being nailed into the tongue of the backing. Q. How is the metal moulding constructed? A. It is made of steel, with a backing and cap- ping, such as shown in Fig. 48. There are various ways of attaching the capping to the backing. One of the best and most modern types, as shown in Fig. 48, is made so that the backing is first at- tached to the wall or ceiling, the screws being countersunk. The capping is then snapped over the backing as can be seen from the illustration- Q. How is corrosion and rusting prevented ? A. The metal is treated by different processes. The Lutz moulding is electro-galvanized, while the National moulding is " Sherardized ", which consists in heating the metal to a high temperature in con- tact with powdered zinc dust. In this way the sur- face of the metal is covered with a zinc-iron alloy which is non-corrosive and rustproof. ELECTRIC WIRING. 117 Fig. 46. Wooden Moulding. -^ '!, ^ =^ Fig. 47. Minimum Dimensions of Moulding. 118 ELECTRIC WIRING. Q. Can metal moulding be used for carrying large feed wires or mains? A. No; the Code restricts its use to circuits of not greater than 660 watts capacity. Q. How many incandescent 16 c. p. lamps would be on a circuit of this capacity? A. Only 12 such lamps, so the Code practically restricts the use of moulding to branch circuits. Q. In the Fig. 48 in which is shown a metal moulding, there is only one slot instead of two slots separated by a tongue as in wooden moulding, why is this? A. In metal moulding, double braided rubber covered twin wires are used. Q- "What is the advantage of this ? A- It makes the wires easier to handle, and also prevents induction troubles, should an alternating current be used. Q. What precaution is always necessary where metal mouldings is used? A. It must always be grounded, since metal is a conductor of electricity. Q. What other precaution is necessary to be ob- served? A. Where wooden moulding is run on walls, it must be protected for a height of at least 5 feet from the floor by two parallel wooden strips, which strips pro.iect slightly above and beyond the mould- ing. The same precaution must be observed with metal moulding, but even more care should be used. ELECTKIC WIRING. 119 iff'W .wwanw i w»i ' jmmRJi w i iw i i » i i- pi wi i> Mi i . i mfnun^ Fig. -is. Metal Moulding. Fig. 19. Conductor Sliowing Strands. 120 ELECTRIC WIRING. Metal moulding should never be brought nearer than 5 feet to the floor, and from there down rigid conduits should be used. Q. Are these protecting strips always necessary? A. No ; where the moulding is run between door jams, in corners, or in places where it will not be liable to mechanical injury, then no protecting strips are necessary. Q. Is the use of single braided wire permitted with metal moulding? A. No; only double braided wires. Where both wooden and metal moulding are used, it, therefore, becomes necessary either to "use a double braided wire throughout the circuit or else splice the double braided wire at the junction box. Q. Is the use of weather proof or slow burning conductors ever permitted with any character of moulding ? A. No; rubber insulated conductors only can be used. Q. Should wooden moulding ever be used in new building? A. No ; as it is not fire-proof, and also is un- sightly in appearance. Only concealed work should be done wherever possible, though the cost is greater. Q. What is the least expensive method of wir- ing? A. Knob and tube wiring. ELECTRIC WIRING- 121 Q. And the next least expensive method of wir^ ing? A. Cleat work and flexible tubing. Q. And the third least expensive method- A. Soft wood moulding. Q. "What is the most expensive method of wiring ? A. Conduit wiring. INSIDE WORK. All Systems and Voltages. General Rules. 14. . Wires. a. Must be of smaller size than No. 14 B. & S. gage, except as allowed for fixture work and pend- ant cord. b. Tie wires must have an insulation equal to that of the conductors they confine. For wire smaller than No. 8 B. & S. gage split knobs or cleats shall be used except at dead ends, and tie wires and knobs will not be approved. Screws must be used for fastening all cleats and knobs which are arranged to grip the wire. e. Must be so spliced or opened as to be both mechanically and electrically secure without solder. The joints must then be soldered unless made with some form of approved splicing device, and covered with an insulation equal to that on the conductors. 122 ELECTRIC WIRINa. Stranded wires (except in flexible cords) must be soldered before being fastened under clamps or binding screws, and whether stranded or solid, when they have a conductivity greater than that of No. 8 B. & S. gage they must be soldered into lugs for all terminal connections, except where an ap- proved solderless terminal connector is used. d. Must be separated from contact with walls, floors, timbers or partitions through which they may pass by non-combustible, non-absorptive, in- sulating tubes, such as glass or porcelain, except at outlets where approved flexible tubing is re- quired. Bushings must be long enough to bush the entire length of the hole in one continuous piece, or else the hole must first be bushed by a continuous water- proof tube. This tube may be a conductor, such as iron pipe, but in that case an insulating bushing must be pushed into each end of it, extending far enough to keep the wire absolutely out of contact with the pipe. e. Must be kept free from contact with gas, water or other metallic piping, or any other conductors or conducting material which they may cross, by some continuous and firmly fixed non-conductor, creating a permanent separation. Deviations from this rule may sometimes be allowed by special permission. ■Where tubes are used, they must be securely fas- tened at the ends to prevent them from moving along the wire. ELECTRIC WIRING. 123 f. Must be so placed in wet places that an air space will be left between conductors and pipes in crossing, and the former must be run in such a way that they cannot come in contact with the pipe accidentally. Wires should be run over, rather than under, pipes upon which moisture is likely to gather or which, by leaking, might cause trouble on a cir- cuit. g. The installation of electrical conductors in wooden moulding, or on insulators, in elevator shafts will not be approved, but conductors may be in- stalled in such shafts if encased in approved metal conduits. For Concealed "Knob and Tube" Work, q. Must have an approved rubber insulating cov- ering. r. Must be rigidly supported on non-combustible, non-absorptive insulators which separate the wire at least one inch from the surface wired over. Should preferably be run singly on separate timbers, or studding, and must be kept at least five inches apart. Must be separated from contact with the walls, floor timbers and partitions through which they may pass by non-combustible, non-absorptive, insu- lating tubes, such as glass or porcelain. Wires pass- ing through timbers at the bottom of plastered par- titions must be protected by an additional tube ex- tending at least four inches above the timber. Rigid supporting requires, under ordinary con- 124 ELECTRIC WIRING. ditions, where wiring along flat surface, supports at least every four and one-half feet. If the wires are liable to be disturbed the distance between sup- ports must be shortened. For Fixture Work. V. Must have an approved rubber insulating cov- ering, and be not less in size than No. 18 B. & S. gage. ELECTRIC WIRING. 125 CHAPTER VIII. Conductors. Q. What is meant by the term conductor? A. Anything that permits the passage of an elec- tric current. Q. Are all substances conductors? A. No; for while all substances, with a few ex- ceptions, permit the passage of an electric current, in some substances the resistance to the current is so great that they are not classed as conductors- Q. What metal is the best conductor? A. Silver. Q. What substance is the worst conductor? A. While a vacuum will not permit the passage of an electric current owing to its extremely high resistance, glass is one of the worst conductors of any substance in daily use. Eight Hand Rule for Induction. 126 ELECTRIC WIRING. Q. We have seen that the ohm is the unit for resistance; is there also a unit for the conductivity of substances? A. No ; such unit has never been adopted, though often suggested. It v^ould be the reciprocal of the ohm, and probably will be adopted at some time in the future. Q. We have seen that owing to its conductivity and low cost as compared to other good conductors, copper is almost entirely used for electric wiring, is pure copper used for this purpose? A. No ; usually refined copper with a conduc- tivity of not leas than 97 per cent. Q. How is the copper wire prepared for all interior wiring? A- It is tinned, which process consists in first "pickling" the copper by running the conductors through an acid solution to remove scale, rust, etc., making the wire clean and bright. The conductors are then passed rapidly through a bath of molten tin, giving then a thin coat of bright tin. This process makes the wires much easier to solder and splice. Q. Are the conductors always made of solid wire? A. No; only for conductors of sizes as large as No. 8 (B. & S. gage). For sizes larger than this, the conductors should be made up of strands of smaller wire, such as shown in Pig. 49, page 119. Q. What advantage is obtained by making the larger size wires in strands ? . - • ELECTRIC WIRING. 127 A. It increases the conductivity of the wire. Q. "Why are the conductors for flexible cords, etc., made up of fine strands? A- In order to make them pliable, Q. How is the maximum current allowed for various size conductors usually determined? A. By tables approved by the National Board of Fire Underwriters, such as Table No. 4, page 57. Q. Does the maximum current allowed depend alone on the size of the wire? A. No; it a] so depends on the character of insulation used. Insulation. Q. How many forms of insulation are now used for conductors? A. Four principal forms, viz. : (1) Rubber insulation with protecting braid or tape. (2) Weather proof insulation. (3) Fire Underwriters* insulation. (4) Slow burning, weather-proof insulation. Rubber Insulation. Q. Is pure rubber used for this insulation? A. No ; it consists of a compound containing from 20 to 40 per cent only of pure rubber. Q. Of what is the composition of the ordinary rubber insulation composed? A. The principal ingredient is French Chalk (Talc). With this substance is mixed the pure rubber, silicate of magnesia, sulphur and red lead. Q. For what purpose is the sulphur added? 128 ELECTRIC WIRING. A. To vulcanize the rubber, which process ren- ders the rubber much stronger mechanically, and also retards decomposition which would otherwise take place at a comparatively low temperature. Q. After the conductors are covered with this rubber composition, what is then done? A. An outer covering of cotton braid is placed over the rubber in order to protect same from me- chanical injury. Q. What are the advantages of such rubber in- sulation ? A. It has a high insulating qualities, and is weather-proof, flexible and strong. Q. What are its disadvantages? A. It will not stand a temperature of over 140 degrees Fah. without deteriorating very rapidly. It also deteriorates under ordinary temperatures- Weather-Proof Insulation. Q. Of what does this insulation consist? A. Of two or more layers of cotton, impregnated with a compound consisting of asphaltum, or some similar material. Q. What are its advantages and disadvantages? A. It is very durable, inexpensive cmd does not deteriorate except when exposed to a high temper- ature. It is also impervious to moisture. It has not high insulating qualities and is more or less inflammable. Q, Where is this insulation mostly used? A. For putrid? conductors for pverhead line ELECTRIC WIRING. " 129 work, for open sheds and in places exposed to the moisture and dampness of the weather. It should never be used in conduits or in any concealed work, but only for exposed work, where the conductors are supported by porcelain or glass insulators. Q. Why is this so necessary? A. Because the insulation has poor insulating qualities, the insulation itself being but little more than a mechanical protection to the conductor. Fire Underwriters' Insulation. Q. Of what does this insulation consist? A. Of cotton braid treated with a fire-resisting compound. Q. Of what is this inflammable compound chiefly composed? A. Of white lead, though sometimes a cheaper compound of oxide of zinc and chalk is used. Q. What are the advantages and disadvantages of this insulation? A. It is durable, incombustible and inexpensive, but it absorbs moisture, and has poor insulating qualities. Q. How should it be installed? A. Always exposed, supported by porcelain or glass insulators, the same as weather-proof insula- tion. It should never be installed in damp places on account of the property it possesses of absorbing or condensing the moisture from the atmosphere. Q. What is meant by slow-burning wire ? A. It is wire covered with an insulation consist- 130 • ELECTRIC WIRING. ing of layers of cotton or thread, all the interstices of which are filled with a fire-proofing compound. Q- Where is it mostly used? A. In hot dry places, such as at the back of large switch boards. Slow burning, Weather-proof Insulation. Q. Of what does this insulation consist? A. Of a combination of the weather-proof and underwriters' insulation. One layer is underwrit- ers* insulation with an inside layer of weather-proof insulation. Q. What advantage is gained by combining these two insulations? A. It permits the wire to be run exposed and in moist places, and at the same time an excess of inflammable covering on the conductor is avoided. The conductor must be always supported on porce- lain or glass insulators. This insulation, the same as weather-proof and Underwriters' insul.ation, de- pends upon the insulators supporting the cables for the insulation and not upon the insulation on the conductors. CODE REGULATIONS. OUTSIDE WORK. All Systems and Voltages. 12. Wires. a. Line wires must have an approved weather- proof or rubber insulating covering- That portion of the service wires between the main cut-out and switch and the first support from the cut-out or ELECTRIC WIRING. 131 switch on outside of the building must have an approved rubber insulating covering, but from the above-mentioned support to the line, except when run in conduit, may have an approved weather-proof insulating covering if kept free from awnings, swinging signs, shutters, etc. b. Must be so placed that moisture cannot form a cross connection between them, and except when run in conduit, not less than a foot apart, and not in contact with any substance other than their in- sulating supports. Wooden blocks to which insul- ators are attached must be covered over their entire surface with at least two coats of water-proof paint. C. Must, where exposed to the weather, be pro- vided with petticoat insulators of glass or porce- lain; porcelain knobs or cleats and rubber hooks will not be approved. Wires on the exterior walls of buildings must be supported at least every fifteen feet, the distance between supports to be shortened if wires are liable to be disturbed. Where not exposed to the weather, low potential wires may be supported on glass or porcelain knobs which will separate the wires at least one inch from the surface wired over, supports to be placed at least every four and one-half feet. f. Must be so spliced or joined as to be both me- chanically and electrically secure without solder. The joints must then be soldered, to insure preser- vation, and covered with an insulation equal to that on the conductors. 132 ELECTRIC WIRING. All joints must be soldered, unless made with some form of approved splicing device. g. Must, where they enter buildings, have drip loops outside, and the holes through which the con- ductors pass must be bushed with non-combustible, non-absorptive, insulating tubes slanting upward toward the inside. For low potential systems the service wires may be brought into buildings through a single iron conduit. The conduit to be equipped with an approved service-head- The inner end must extend to the service cut-out, and if a cabinet is required by the Code must properly enter the cabinet. h. Electric light and power wires must not be placed on the same cross-arm with telebraph, tele- phone or similar wires, and when placed on the same pole with such wires the distance between the two inside pins of each cross-arm must not be less than twenty-six inches. i. The metallic sheaths to cables must be per- manently and effectively connected to "earth." 2. Conductors. From generators to switchboards, rheostats or other instruments, and thence to outside lines : — a. Must be in plain sight or readily accessible. "Wires from generator to switchboard may, how- ever, be placed in a run-way in the brick or cement pier on which the generator stands. When protec- tion against moisture is necessary, lead covered cable or iron conduit must be used. ELECTRIC WIRING. 133 b. Must have an approved insulating covering as called for by rules in Class "C" for similar work, except that in cen,tral stations, on exposed circuits, the wire v^hich is used must have a heavy braided, non-combustible outer covering- Bus bars may be made of bare metal. a. Must be so placed as to render to a minimum the danger of communicating fire to adacent com- bustible material. Switchboards must not be built up to the ceiling, a space of three feet being left, if possible, between the ceiling and the board. The space back of the board must be kept clear of rubbish and not used for storage purposes. b. Must be made of non-combustible material or of hardwood in skeleton form, filled to prevent ab- sorption of moisture. If wood is used all wires and all current carry- ing parts of the apparatus on the switchboard must be separated therefrom by non-combustible, non-absorptive, insulating material. c. Must be accessible from all sides when the connections are on the back, but may be placed against a brick or stone wall when the wiring is en- tirely on the face. If the wiring is on the back, there must be a clear space of at least eighteen inches between the wall and the apparatus on the board, and even if the wiring is entirely on the face, it is much better to have the board set out from the wall. i;ji ELECTRIC WIRING. d. Must be kept free from moisture. e. On switchboards the distances between bare live parts of opposite polarity must be made as great as practicable, and must not be less than those given for' tablet-boards. 16 Table of Carrying Capacity of Wires. a. The following table, showing the allowable car- rying capacity of copper wires and cables of ninety- eight per cent conductivit.y, according to the stand- ard adopted by the American Institute of Electrical Engineers, must be followed in placing interior con- ductors. (See Table No. 4, page 57.) For insulated aluminum wire the safe carrying capacity is eighty-four per cent, of that given in the following tables for copper wire with the same kind of insulation. ELECTRIC WIRING. 135 CHAPTER IX. Construction of Fuses and Safety Devices. Q. What have we seen is the purpose of a fuse? A. To protect the electric conductors, appli- ances and machinery from excessive currents, by melting or opening the circuit should the current become excessive- Q. Of what are fuses usually composed? A. Of lead, tin or some alloy of these metals, they being selected owing to their low fusing point. Q. What metal is used for very heavy currents, and what metal for very light currents? A. Copper is used for heavy currents such as currents from 25 amperes to over 1000 amperes. Resistance Box. 136 ELECTRIC WIKING. while platinum is used for very light currents. The metals zinc and aluminum are, also, coming into use for ordinary currents. Q. What form of fuse was first used? A. Short fuse wires. Such wires, with a heavier metal strip attached at end of the wire as shown in Pig. 15, are still in general use. The earlier forms of fuse wire was soon replaced by the Edison fuse plug, which plug is still in general use. In Fig. 51 is shown an ordinary Edison fuse plug. Q. What are the advantages of the Edison fuse plug over the ordinary fuse wire? A. It is interchangeable, and can be quickly installed or replaced. It is also much safer- Q. Why is it safer? A. Because it is enclosed, so that should it blow or melt the danger of fire or injury is almost en- tirely removed. Q. What are open link fuses? A. Such a fuse as shown in Fig. 52- Q. What advantage has this type of fuse? A. Its low first cost, and of being easily detected when blown or melted from an excessive heat. Q. What is the most recent and improved type of fuse? A. The cartridge fuse, which consists of a fuse centrally placed in a tube or envelope of incombust- ible material, within which the melting or volatili- zation of the fuse may take place without any dan- ger from fire or injury to the surrounding objects. ELECTRIC WIRING. 137 M s CO U5 be 138 ELECTRIC WIRING. In Fig. 53 is shown a type of cartridge fuse in gTiJieral use. Q. "What especial advantage has the cartridge fuse over the Edison fuse plug and over the open link fuse? A. It can be used in higher voltages without "arcing." When the 220 volt lamp was first in- troduced, it was found that both the Edison fuse plug and the open link fuse would arc at a voltage of 220. In order to protect circuits carrying this voltage the cartridge fuse was constructed, which prevented the forming of an arc when the fuse was blown by a short circuit or overload current. Q. How are cartridge fuses constructed? A. Of vulcanized fibre or paper tubes, which are filled with a porous material, usually chalk with soapstone. In Fig. .54 is shown a sectional view of one of these cartridge fuses from which can be seen their construction. Q. What are the disadvantages of cartridge fuses ? A. They are not suitable for heavy currents, being adapted only to currents not exceeding 500 Aolts. It is, also, difficult to locate a blown car- tridge fuse; and, lastly, they are more expensive than the other type of fuses. Q. What is the safest and surest way of finding a blown fuse? A. Using a test lamp across the outside terminals of a pair of fuses when connected in circuit, ELEC^TliKJ WlKiiNG. 139 c rs, -4_J Fig. 52. All Opeu Link Fuse. Fig. 53. Type of Cartridge Fuse. ^ COppEK ftl^ROLS: wfm^^jjjji j^j,,.., )i >,^, ,> ,ij> jj, j-j^jj^ytffftff^^K^f^ 1B& s» Alts CnAVlBEe fuse VVIRE flULlNG / Fig. 54. Sectional View of Cartridge Fuse. 140 ELECTRIC WIRING. Q. For very heavy currents, such as 1000 am- peres, what character of fuses must be used? A. Copper fuses- Q. Why is copper selected for heavy currents? A. On account of its high fusing point, which is 1,931 degrees Pahr. Q. What is the fusing point of lead? A. Only 617 degrees Fahr., and it is for this reason that lead and tin are used for lighter cur- rents. Q. What is the fusing point of tin? A. Only 551 degrees Fahr. Q. Has copper as high a fusing point as iron? A. No ; the fusing point of cast iron is 2,192 de- grees Fahr., and of wrought iron 2,912 degrees Pahr. Q. Why, then, is not iron used for fuses on heavy currents? A. Because of its high specific heat (the number of heat units required to raise it one degree in temperature), and also because its fusing point is too high for practical use. Q. What objection is there to the use of copper for heavy currents? A. On acount of the high temperature at which it melts (fusing point), it heats the contact switches to an injurious extent even before it reaches this point, thereby causing, not only inconvenience, but often considerable damage. ELECTRIC WIRING. 141 Q. Are fuses blown only by an overload current, or by short circuits? A. No ; they are often blown simply from heat due to a poor contact. Q. How is the melting (fusing) point of ordinary fuses carrying not over 500 amperes determined? A. By ascertaining the maximum temperature that will melt them within five minutes on a mini- mum current. For larger fuses it requires a longer time than this to reach the fusing point. Q. What three factors must be considered in the construction of all types of fuses? A. (1) The length of the fuse. (2) The form of the fuse. (3) The size of the terminal of the fuse. Q. Why is a long fuse preferable to a short fuse? A. It will prevent the burning of the terminals when the fuse blows. Q. What is a general rule for the distance of the terminal screws? A. The terminal screws should not be nearer to- gether than one inch on 100 volt circuits, and one additional inch should be allowed for each 100 volts in addition; that is, two inches space for 200 volts, three inches space for 300 volts, etc. See Tables Nos. 8 and 9. Q. Why is the form and the size of the terminals so important? A. In order to insure a good contact. Q. How are fuses rated? 142 ELECTRIC AYIRING. A. According to the Code they must be stamped with about 80 per cent of the maximum current Avhieh the can carry indeflnitey, thus allowing about 25 per cent overloard before the fuse melts. Q. A fuse, therefore, for a 100 ampere current must blow (melt) on a 75 ampere current? A. No ; while it must carry indefinitely, a 75 ampere current, it must blow on a 25 per cent over- load current; that is, on a 100 ampere current. CODE REQUIREMENTS. INSIDE WORK. 17. Switches, Cut-Outs, Circuit-Breakers, Etc.. a. On constant potential circuits, all service switches *nd all switches controlling circuits sup- plying current to motors or heating devices, and all fuses, unless otherwise provided, must be so ar- ranged that the fuses will protect and the opening of the switch will disconnect all of the wires; that is, in the two-wire system the two wires, and the three-wire system the three wires, must be protected by the fuses and disconnected by the operation of the switch. "When installed without other automatic overload protective devices automatic overload,circuit break- ers must have the poles and trip coils so arranged as to afford complete protection against overloads and short circuits, and if also used in place of the switch must so arranged that no one pole can be ELECTRIC WIRING. 143 opened manually without disconnecting all the wires- This, of course, does not apply to the grounded circuit of street railway systems. , b. Must not be placed in the immediate vicinity of easily ignitable stuff or where exposed to inflam- mable gases or dust or to flying of combustible ma- terial. c. Must, when exposed to dampness, either be enclosed in a moisture-proof box or mounted on porcelain knobs. The cover of the box must be so made that no moisture which may collect on the top or sides of the box can enter it. 22. Switches. a. Must be placed on all service wires, either over- head or underground, in the nearest readily acces- sible place, to the point where the wires enter the building, and arranged to cut off the entire current. Service cut-out and switch must be arranged to cut off current from all devices including meters. In risks having private plants the yard wires run- ning from building to building are not considered as service wires, so that switches would not be re- quired in each building if there are other switches conveniently located on the mains or if the gener- ators are near at hand. c. Single pole switches must never be used as service switches nor placed in the, neutral wire of 144 ELECTRIC WIRING. a three-wire system, except in the two-wire branch or tap circuit supplying not more than 660 watts. 4. Resistance Boxes and Equalizers. a. Must be placed on a switchboard, or at a distance of at least one foot from combustible material, or separated therefrom by a slab or panel of non-combustible, non-absorptive, insulating ma- terial such as slate, soapstone or marble, somewhat larger than the rheostat, which must be secured in position independently of the rheostat supports. Bolts for supporting the rheostat shall be counter- sunk at least %-inch below the surface at the back of the slab and filled. For proper mechanical strength, slab should be of a thickness consistent with the size and weight of the rheostat, and in no case to be less than % inch. CONSTANT-POTENTIAL SYSTEMS- General Rules — All Voltages. 21, Automatic Cut-Outs (Fuses and Circuit-Break- ers). a. Must be placed on all service wires, either overhead or underground, in the nearest accessible place to the point where they enter the building and inside the walls, and arranged to cut off the entire current from the building. In risks having private plants, the yard wires running from building to building are not considered as service wires, so that cut-outs would not be re- ELECTRIC WIRING. 145 quired where the wires enter buildings, provided that the next fuse back is small enough to properly protect the wires inside the building in question. b. Must be placed at every point where a change is made in the size of wire (unless the cut-out in the larger wire will protect the smaller). C. Must be in plain sight, or enclosed in an ap- proved cabinet, and readily accessible. They must not be placed in the canopies or shells of fixtures. Link fuses may be used only when mounted on approved slate or marble bases and must be en- closed in dust-tight, fire-proofed cabinets, except on switchboards. d. Must be so placed that no set of incandescent lamps requiring more than 660 watts, whether grouped on one fixture or on several fixtures or pendants, will be dependent upon one cut-out. The fuse in the branch cut-outs must not have a rated capacity greater than 6 amperes on 110 volt systems, and 3 amperes on 220 volt systems. On open work in large mills approved link fused rosettes may be used at a voltage of not over 125 and approved enclosed fused rosettes at a voltage of not over 250, the fuse in the rosettes not to ex- ceed 3 amperes, and a fuse of over 25 amperes must not be used in the branch circuit. Circuit-breakers must not be set more than 30 per cent, above allowable carrying capacity of the wire, unless a fusible cut-out is also installed on lie ELECTEIC WIRING. the circuit, in which event the circuit-breaker may be set as high as 100 per cent, above such capacity. In the arms of fixtures carrying a single socket a No. 18 B. & S. gage v^ire supplying only one socket will be considered as properly protected by a six ampere fuse. f. Each phase of A. C. motor circuits, except on main switchboard or when otherwise subject to expert supervision, must be protected by an ap- proved fuse, whether automatic overload circuit breakers are installed or not. Single phase motors may have one side protected by an approved auto- matic overload circuit breaker only if the other side is protected by an approved fuse. For circuits having a raaximum capacity greater than that for which enclosed fuses are approved circuit breakers alone will be approved. ELECTRIC WIRING. 147 t 1 r 1 ; - _..„.. ■- F 1 — -y-- "1 " ' 6I-«00 AMPCRCS 1 Form 2. CARTRIDGE FUSE-Knife Blade Contact. D E F G Diameter of Ferrules or Thickness of Terminal Blades. . Inches, Min. Length of Ferrules or of Ter- minal Blades outside of Tube. Inches. Dia. of Tube. Inches Width of Terminal Blades. Inches. Bated Capacit\ Amperes. '%8 » E 0-30 31-60 H 1 1% 2AC t 2 u. 01-100 101-200 201^00 ^01-600 K % 1 ^ £ 0-30 31-60 K ^H 1 2y, 61-100 101-200 201-400 Table No. 8. Dimensions of Standard Cartridge Fuse. Knife Blade Contact. 148 ELECTRIC WIRING. Form 1. CARTRIDGE FUSE-Ferrnle Contact. Eaterl Capttoity. Amperes. A B C Voltage. Length over Terminals. Inches. Distance between Contact Clips. Inches. Width of Contact Clipa. Inches. 0-250 (V-30 81-60 B 2 i2 S 1 IK M « 61-100 101-200 S(ll-400 401-600 i e 6 1^ 2B1-600 0-30 31-60 i 6 4 61-100 101-200 2o:-«oo e 1 8 S Table No. 9. Dimensions of Standard Cartridge Fuse. Ferrule Contact. ELECTRIC WIRING. 149 CHAPTER. X. PANELS AND CUT-OUT CABINETS. Q. "What is a cut-out cabinet? A. Any inclosure of space arranged for the re- ception of fuses or cut-outs. In Fig. 55 is shown a form of a cut-out cabinet. Q. How are these cabinets constructed? A. They consist of panel distributing boards placed in boxes, the inner sides and the door of the box being lined with asbestos paper, slate or some other good insulating material. Rheostat. 150 ELECTRIC WIRING. Fig. 55. A Cut Out Cabinet. ELECTRIC WIRING. 151 Q. How is the present type of panel board con- structed ? A. It is arranged with bus-bars running ver- tically up and down the board with cross connect- ing bars extending horizontally in the branch cir- cuit or main connections- These horizontal bars are arranged to permit the insertion of the fuses. Q. "What type of fuses are used on panel boards ? A. Three types of fuses, viz. : (1) The fuse plug, (2) The link fuse, and (3) The cartridge fuse. In Pig. 56 is shown a panel board with plug fuses. In Fig. 57 is shown a board with link fuses, and in Fig. 58 is shown a panel board Switch. Q. How are the connections made between the conductors and bus bars on these panel boards? A. It depends on the size of the conductor. For all sizes smaller than No. 8 B. & S. gauge binding screws with copper washers are used. For sizes larger than No. 8 B. & S. wire, special copper lugs are provided for this purpose, the wires being in- serted in the lug and then "sweated" in place. Q. What is the disadvantage in making screw connections? A. They are especially objectionable where stranded or large wire is used. Where stranded wire is used, it is hard to get all the strands in contact with the crews head or copper strap. With large wire, it is also difficult to get the entire con- ductor in actual contact, a portion usually being left out, which portion carries little or no current. 152 ELECTRIC "WIKING. m £ ELECTRIC WIRING. 153 Fig. 58. A Panel Board Switch. Two Poles — 125 Volts — 15 Amperes. 154 ELECTEIC WIRING. CHAPTER XI. Outlet Boxes. Q. What is an outlet box? A. It is a device placed at any outlet for the purpose of providing a terminal for the conduits. It is, also, a space provided for making the connec- tions between the branch circuit vs^ires and the out- let appliances. These boxes are usually made of iron or steel in tvs'o parts, the box and the cover. In Fig. 59 is shown an outlet box, without the cover, and in Fig- 60 a covered box. Q. What is a junction box? A. It is an iron casing or box used in under- ground distributing systems in which the feeders and mains are joined ; and, also, other junctions are made. This box is sometimes called a fishing box. In Fig. 61 is shown an ordinary junction box. Q. What is the essential difference between an outlet box and a junction box? A. An outlet box is used to allow wires to pass out to lamps, chandeliers, etc., while a junction box is used in making the junction between conduits, etc. Q. Are outlet boxes required on all circuits? A. No; they are not required for circuits run in moulding, for wiring installed in flexible tubing, or for cleat work or for knob and tube wiring. ELECTRIC WmiNG. 155 ^. , ,0-60 Outlet Bo. aud Cover. Figs. -JJ ""• 156 ELECTRIC WIRING. Q. In what forms are outlet boxes usually con- structed ? A. In two general forms, viz. : the so-called uni- versal type, adapted for general use without change, as the openings in same can be easily made with- out drilling ; and the special box, in which openings are already made at fixed points for the conduits to enter. Q. "What are the advantages and disadvantages of the Universal type of outlet boxes? A. As the tubes may be brought into the box from any side, or into the back, in ordering it is only necessary to state whether the boxes are to be used for gas or electric fixtures, or for both. Their principal disadvantage is that being adapted for general use, they are not especially adapted to any particular use, their construction, therefore, being necessarily poorer than if constructed for one specific use. Q. What are the advantages and disadvantages of the Special type of boxes ? A. As this type of box is designed for a par- ticular use, their construction for that particular work is of the best. But, as it is necessary to have a special box for each particular work, it requires a large stock of these boxes to be carried. It is, also, difficult to order these boxes, as the work for which they are to be used must be accurately de- scribed in each instance. ELECTRIC WIRING. 157 Closed Open lor Iticipeoilon Pig. 61. A Junction Box. 158 ELECTRIC WIRING. OUTLET INSULATORS. Q. What are the advantages of an insulated out- let box? A. It provides a fireproof terminal for the con- duits, and also decreases the probability of ground or short circuits. Q. How are the boxes insulated? A. The inside of the box is enameled with por- celain lining. As this is expensive, Japan enamel is often used for insulating these boxes. This enamel is much less expensive and is fairly good. CODE REQUIREMENTS. Wires. a. Where entering cabinets must be protected by approved bushings, which fit. tightly the holes in the box and are well secured in place. The wires should completely fill the holes in the bush- ings so as to keep out the dust, tape beiiig used to build up the wires if necessary. On concealed knob and tube work approved flexible tubing will be accepted in lieu of bushings, providing it shall extend from the last porcelain support into the cabinet- b. Must not be laid in plaster, cement or similar finish, and must never be fastened with staples. d. Twin wires must never be used, except in con- duits, or where flexible conductors are necessary. e. Must be protected on side walls from mechan- ical injury. When crossing floor timbers in cellars, or in rooms where they might be exposed to injury, ELECTRIC WmiNCi. 159 wires must be attached by their insulating supports to the under side of a wooden strip, not less than one-half inch in thickness, and not less than three inches in width. Instead of the running-boards, guard strips on each side of and close to the wires will be accepted. These strips to be not less than seven-eighths of an inch in thickness, and at least as high as the insulators. Protection on side walls must extend not less than five feet from the floor and must consist of substantial boxing, retaining an air space of one inch around the conductors, closed at the top (the wires passing through bushed holes) or approved metal conduit or pipe of equivalent strength. When metal conduit or pipe is used, the insula- tion of each wire must be reinforced by approved flexible tubing extending from the insulator next below the pipe to the one next above it. 25. Interior Conduits. a. No conduit tube having an internal diameter of less than five-eighths of an inch shall be used. Measurements to be taken inside of metal conduits. b. Must be continuous from outlet to outlet or to junction boxes, and the conduit must properlj' enter, and be secured to all fittings and the entire system must be mechanically secured in position. In case of service connections and main runs, this involves running each conduit continuously 160 ELECTRIC WIRING. into a main cut-out cabinet or gutter surrounding the panel board, as the case may be. c. Must be first installed as a complete conduit system, without the conductors. d. Must be equipped at every outlet with an approved- outlet box or plate. Outlet plates must not be used where it is prac- ticable to install outlet boxes. The outlet box or plate must be so installed that it will be flush with the finished surface, and if this surface is broken it shall be repaired so that it will not show any gaps or open spaces around the edge of the outlet or plate- e. Metal conduits where they enter junction boxes, and at all other outlets, etc., must be provided with approved bushings or fastening plates fitted so as to protect wire from abrasion, except when such protection is obtained by the use of approved nipples, properly fitted in boxes or devices. f. Must liave the metal of the conduit perma- nently and effectually grounded. 24.Armored Cables. a. Must be continuous from outlet to outlet or to junction boxes, and the armor of the cable must properly enter and be secured to all fittings, and the entire system must be mechanically secured in posi- tion. In case of service connections and main runs, this involves running such armored cable continuously ELECTRIC WIRING. 161 into a main cut-out cabinet or gutter surrounding the panel board, as the case may be. b. Must be equipped at every outlet with an approved outlet box or plate, as required in conduit vi^ork. Outlet plates must not be used where it is practicable to install outlet boxes. The outlet box or plate shall be so installed that it will be flush with the finished surface- c. Must have the metal armor of the cable per- manently and effectively grounded. Armor of cables and gas pipes must be securely fastened in metal out-let boxes so as to secure good electrical connection. Where boxes used for centers of distribution do not afford good electrical connec- tion the armor of the cables must be joined around them by suitable bond wires. 162 ELECTRIC ^YIRIXG. CHAPTER XII. The Alternating Current. Q. Does the current alternate back and forth throughout the entire circuit as the coils pass the different sets of poles? A. Yes; it flows out of the machine and through the entire length of the circuit as the coils pass under the north poles and back again to the ma- chine, and then out again and back over the circuit as the coils pass under the adjoining south poles, and these alternations continue so long as the arm- Faraday's Ring. ELECTRIC WIRING. 163 ature is in motion. In Fig. 62 is shown the wave form of an alternating current. The horizontal line in this illustration usually de- notes a zero current, that is when no current is flowing; or it may be taken to indicate zero electro- motive force. The curve represents the current, or the corresponding elctro-motive forces. The further the curve is from the line the greater is the cur- rent or the electro-motive force. When the curve is above the line, the direction of the current is opposite to that corresponding to the positions be- low the line. Therefore, as seen from the illustra- tion, the current is alternately in opposite direc- tions, having periods of maximum and minimum intensity as it passes from one direction to the other direction. AH the phases in the intensity of the current and the electro-motive force can be shown by a curve to correctly represent these phas- es, and such a curve is usually called the sine curve of generation, as shown in Fig. 63. The ordinates of the curve can be taken to represent the current's strength or the electro-motive force. The ordinates are usually taken to represent the electro-motive force, and when so used, the ordinates above the line are taken as positive, and those below as nega- tive. A. What is a cycle? A. One cycle is composed of two such alterna- tions of the current, hence the coils must pass under 164 ELECTRIC WIRING. Fig. 62. Wave Form of an Alternating Current 36 O' S70 Fig. 63. Sine Curve of Generation. ELECTRIC WIRING. 165 both the north and the adjoining south poles to produce one cycle. Q. Suppose we had only one coil in a bi-polar field; that is, a machine with only two poles; how far would the armature have to revolve to produce one alternation? A- It would have to make one-half of a revolu- tion. Q. How far to produce one cycle? A. It would have to make one complete revolu- tion. Q. What do we mean by frequency? A. It is the number of cycles occurring per sec- ond. Q. What frequency is required for arc lamps? A. A frequency of not less than 40 cycles per second. Q. With a bi-polar machine, how often would this require the armature to revolve? A. Forty complete revolutions per second, or 2,400 per minute. Q. Is this not too fast for safety and economical work? A. Yes; so the number of poles is increased. Q. How does this decrease the speed? A- Instead of making one complete revolution in order to generate one cycle, as in a bi-polar ma- chine, only a quarter, a sixth, an eighth or a for- tieth of a revolution must be made, depending on 166 ELECTRIC WIRING. whether the machine has eight, twelve, sixteen, or eighty poles ; since ^ve have seen that to produce one cycle it is necessary only for the coil to pass two poles vith opposite polarities; that is, a north and a south pole or a south and a northpole. Q. "Why -were direct currents better understood than alternating currents in the early development of electi-icily? A. Because the first electric currents known were derived from batteries. All electric currents from batteries are direct currents ; that is, they flow continuously in one direction around the cir- ciiit, and hence are also called continuous or direct currents. Q. "What character of current is now most gen- erally used? A. Alternating currents, as they possess many valuable properties not possessed by direct currents. Q. For what work are alternating currents now much used? A. For long distance transmission work, as well as electric lighting. Q. What frequencies are preferred for lighting and for power work? A. A frequency of 50 cycles for lighting, and a frequency of 25 cycles per second for long distance transmission work. Q. Does the electro-motive force whieli gener- ELECTRIC WIRING. 167 ates these currents also alternate, and with the same frequency as the current itself? A. Yes; for instance, where the frequency of the current is 50 cycles per second, the electro-motive force has 100 pulsations per second, 50 of them tending to drive the current forward, and 50 of them tending to drive it back. Q. As each alternation, or impulse, is produced l)y a coil, or coils, passing a pole, does it not re- quire an excessive number of revolutions of an en- gine, or turbine, to drive the armature or rotor? A- No ; it is only necessary to increase the num- ber of electro-magnets, so that in one revolution of the engine, or turbine, several opposite poles will fly past the fixed conductors, or vice versa; there- fore, instead of only one impulse of the electro- motive force for each revolution, there will be sev- eral, each impulse inducing one alternation of the current. Q. How must the electro-magnets be arranged? A. The electro-magnets must be so arranged that their poles shall be alternately north poles and south poles, as shown in Fig. 64. With this ar- rangement, while a north pole is passing the con- ductors, the induction will act one way around the coil; and while the north pole is retreating and a south pole is coming up, the induction will act the other way around the circuit, each of these induc- tions causing one alteration of the current. 168 ELECTRIC WIRING. O o ELECTRIC WIRING. 169 Q. Explain the frequency and arrangement of the poles on an eight-pole alternator. A. In Fig. 65 is shown a magnet-wheel which has eight poles. It will be seen that there are four north and four south poles, which are so ar- ranged as to have alternately north and south poles. In one revolution, therefore, there will be induced eight alternations or four complete cycles. If a frequency of 50 cycles is desired, the magnet wheel must be driven at a speed of 12i/^ revolutions per second or 750 revolutions per minute. Q. Suppose the magnet wheel had only four poles, then how fast would it have to be driven to produce 50 cycles per second? A. If the wheel had only four poles, then it would produce only four alternations, or two com- plete cycles, per second; that is, 120 cycles per min- ute. Thus, to produce 50 cycles per second, the magnet wheel would have 'to be driven at a speed of 25 revolutions per second, or 1,500 revolutions per minute. Q- Could we get such speed from a steam en- gine? A. No; since a slow-speed engine rarely makes over 150 revolutions per minute ; and even with a high speed engine we could not with economy get over 350 revelations per minute. Q. Could we not get the 1,500 revolutions per 170 blectkk; wiring. Fig. 65. An Eight-Pole Alternator. ELECTRIC AYIRIXG. 171 minute necessary to drive this alternator from a steam turbine? A. Yes ; all speeds of more than 1,000 revolutions per minute are suitable only for turbines. Q. How do we find the frequency of a current? A. By simply dividing the number of revolu- tions per minute hy 60, aud then multiplying l)y the numJ)er of pairs of poles. Q. We have seen that in direct-current machines the armature is always made to revolve between the poles in order to generate the current. Is this equally true for alternators? A. No ; the armature in alternators usually is made to stand still, and the field, or magnet-poles, made to revolve around it. Only in small machines does the armature revolve. Q. What is such an armature called? A. The stator, as it stands still. Q. What is the revolving fields called? A. The rotor, as they rotate- Q. What, then, would be the definition of a stator? A. It is that part of a dynamo, or motor, whether the armature or the field, which remains at rest or stands still during the operation of the machine, as distinguished from the rotor, or that part which rotates. Q. What is the formula for calculating the volt- age at which an alternator works? 172 ELECTRIC WIRING. A. E = nXfXzXk^ 10^ In this formula n represents the number of mag- netic lines in the flux from any one pole; z, the number of conductors in series with one another in any circuit of the armature ; f , the frequency ; k, a coefficient depending on the shape of the poles and distribution of the windings, being usually 2.2; 10* is equal to 100,000,000 lines of magnetic force; while E is the voltage of the alternator to be so ascertained. Q. Why do we divide by 10» or 100,000,000? A. Because to generate one volt there must be 100,000,000 magnetic lines of force cut per second. Q. What three leading types of alternators are there ? A. (1) Small machines having stationary field magnets and revolving armatures, and, therefore, resembling multi-polar direct current machine. (2) Large machines with revolving magnet-wheels or fields, and with stationary armatures. (3) High speed machines for steam turbine driving, having external stationary armatures and internal revolv- ing field-magnet systems. Q- What are slip-rings? A. Where alternators have revolving armatures, a sliding contact is necessary to connect the revolv- ing coils with the external circuit." Such sliding contacts are made by connecting the ends of the armature windings to insulated metal rings which ELECTEIC WIRING. 173 are fixed on the shaft, and such rings are known as slip-rings. Against these metal rings the collect- ing brushes of metal or carbon press, and the cur- rent so collected is thus conveyed to the external circuit. Q. How many of these slip-rings, or collectors, are necessary for each machine? A. That depends on the number of circuits sup- plied by the machine. For a single circuit alterna- tor, which is a single-phase machine, two of such slip-rings are necessary, while for a two-phase ma- chine, as such machines have four circuits, four slip-rings are necessary. For a three-phase machine only three slip-rings are required, as only three circuits are supplied with such a machine. Q. When the armature is stationary and the fields revolve, how are the poles magnetized? A. The magnetizing current is supplied from a direct-current machine, called an exciter, and as the poles are revolving, sliding contacts are necessary. Two slip-rings are fixed on the shaft to receive the exciting current from the contact-brushes and to convey it to the magnetizing windings on the poles. Q. What effect has the shape of the armature coils on the wave form of an alternator? Q. The wave-form depends largely on the shape of the magnet-poles, and not upon the armature coils, provided they have a span equal to the pole- pitch. If the poles are pointed, the wave-form will 174 ELECTRIC AVIEIXG. be peaked ; if they are broad and blunt, the wave- form will be well rounded, or with flat tops, as shown in Fig. 66. If the poles are narrow, the waveform will then be pointed or peaked, as shown in Fig. 67. If there are wide slots in the periphery of the armature core, then there will be ripples in the wave-form caused by distortions in the current, the same as shown in Fig. 68. VIRTUAL VALUE OF CURRENT. Q. What do you mean by the virtual value of an alternating voltage? A. It is the fixed unit taken to measure the volt- age of an alternating current. Such a unit is nec- essary, as the current continually varies, rising and falling, then reversing its direction, and again rising and falling. Q. Explain why it is necessary to have such a fixed unit to find the value of an alternating cur- rent. A. Because the voltage of an alternating current continually varies, and so a mean or average value must be ascertained in order to obtain the true value of the current. For instance, let us suppose we have a 200-volt alternator, then the voltage varies during one period, or the time occupied in performing one complete cycle, from up to +200 volts, and then back to 0, then to — 200 volts, and finally back to 0, which completes the cycle in one period of time. We cannot take an average of all these values as ELECTRIC WIRING. 175 Pig. 66. Wave Forms Showing Broad and Blunt Poles. Fig. 67. Wave Forms Showing Narrow Poles. Fig. 68. Wave Forms Showing Wide Slots in Armature. 176 ELECTRIC WIRING. the true value, because the value of the current will depend to a certain extent on the vs^ave-form of the curve, which depends on the shape of the poles, as we have seen. We must, therefore, adopt a differ- ent way to determine accurately the true value, and that is done by taking the square-root of the mean of the squares of all the values, which is called the quadratic mean. This value is, therefore, called the "virtual" mean, as it is the real or true value, and not the apparent value. Q. Why is it called the quadratic mean? A. Owing to the mathematical method of calcu- lation used to ascertain the same. EXAMPLES. Q. Explain the method of calculation used, for instance, in finding the virtual amperes of a six- ampere alternating current? A- If we divide the period of such a current into 12 equal parts, we find the following values in one cycle : 0+3+5+6 + 5+ 3 + —3—5—6—5—3—0 Now, the square of these numbers are : + 9 + 25 + 36 + 25+9 + + 9 + 25 + 36 + 25 + 9 + The sum of these squares, therefore, vrould be 18 + ELECTRIC WIRING. 177 50 + 72 + 50 + 18, or 208, and dividing this by 12 to find the mean or average of same, would give us 17.33. But to get the virtual, or quadratic mean, we must take the square root of this average, which will give us 4.16 as the virtual amperes of such a current. Q. Is there not a shorter method of ascertain- ing the virtual value of a current? A. Yes ; by simply multiplying the number of amperes by the fraction 0.707, since the virtual value of a current is equal to .707 of its maximum value. Therefore, a current having a maximum value of 6 amperes has only a virtual value of 6 X -707 = 4.24 amperes. Q. Can we find also the virtual value of the electro-motive force, or voltage, of any alternating current ? A. Yes; by simply multiplying the maximum vditage by .707. This will give us the virtual value of the voltage. For example, an alternating cur- rent having a maximum voltage of 150 volts would have 150 X .707 = 106.0 actual voltage. Q. "Why do we take the fraction .707 as the virtual value of the maximum value of the voltage, or current, of any alternating current? A. Because it is that much of the sine-function of the time of the alternations of the voltage, or of the current, of an alternating current which fol- lows a smooth-wave form. 178 ELECTRIC WIRING. Q. Do voltmeters and ampere-meters indicate the virtual voltage and current, or only the maximum voltage and current. A. They indicate the virtual voltages and cur- rents, or amperages. For instance, if a voltmeter records 100 volts, the voltage is actually varying between + 141.4 and — 141.4 volts, but the virtual voltage is only 100. Q. Can we use the fraction .707 in finding the virtual value of all alternating currents? A. No; it can be used only when the poles give smooth wave-forms. Q. Is it necessary to find also the virtual values of direct currents? A. No; because such currents are constant, and hence do not have a varying value- Q. Can the virtual voltage and current of an alternating current be ascertained also by a com- parison with a direct current? A. Tes; an alternating electro-motive force or current which produces the same deflection on an electro-static voltmeter as that produced by a di- rect electro-motive force; or, an alternating current which produces the same heating effect as a direct current, have the same value. This value is the virtual electro-motive force and current of the al- ternating current, which may be ascertained by the other methods already explained. Q. "What is an electro-static voltmeter? ELECTRIC WIRING. 179 A. It is an instrument used for measuring the voltage either of a direct or an alternating current, being based on the principle that two opposttely charged bodies always attract each other. It is im- material whether the charge is positive or negative, the force of attraction is just the same in each case ; therefore, this instrument can be used equally well for alternating or direct currents. CODE REQUIREMENTS. 1. Generators. a. Must be located in a dry place. b. Must never be placed in a room where any hazardous process is carried on, nor in places where they would be exposed to inflammable gases or flyings of combustible materials. c. Must, when operating at a potential in excess of 550 volts, have their base frames permanently and effectively grounded. Must, when operating at a potential of 550 volts or less, be thoroughly insulated from the ground wherever feasible. "Wooden frames used for this purpose, and wooden floors which are depended up- on for insulation where, for any reason, it is neces- sary to omit the base frames, must be kept filled to prevent absorption of moisture, and must be kept clean and dry. d. Constant potential generators, except alter> nating current machines and their exciters, must 180 ELECTRIC WIEING. be protected from excessive current by safety fuses or equivalent devices of approved design. For two-v7ire, direct-current generators, single pole protection will be considered as satisfying the above rule, provided the safety device is located in the lead not connected to the series winding. "When supplying three-wire systems, the generators must be so arranged that these protective devices will come in the outside leads. For three-wire, direct-current generators, a safety device must be placed in each armature, direct-cur- rent lead, or a double pole, double trip circuit breaker in each outside generator lead and corre- sponding equalizer connection. e. Must each be provided with a name-plate, giving the maker's name, the capacity in volts and amperes, and the normal speed in revolutions per minute. PROPERITIES OF ALTERNATING CURRENTS. Inductance. Q. What is inductance? A. It is the same as self-induction. It is, there- fore, that property in virtue of which. a finite elec- tro-motive force impressed (supplied for an outside source) on a circuit does not immediately generate the full current, due to the resistance of the circuit ; and which, when the electro-motive force is with- ELECTRIC WIRING. 181 drawn, requires a finite time for the current to fall to its zero value. Q. "What effect has inductance on an alternating current ? A. It retards the flow of the current entering the line. Q- Is it the same as the true or ohmic resistance of a conductor? A. No ; it is a spurious resistance, or a counter- electro-motive force. It opposes the electro-motive force tending to send a current through the circuit. It, therefore, develops a condition similar to increas- ing the ohmic resistance in the conductor or circuit. Q. Is the effect of inductance as wasteful of en- ergy as ohmic resistance? A. No ; as it only affects the impressed electro- motive force. It is a secondary current due entirely to changes taking place in the curi-ent itself, and not from an impressed (outside) source. Q. Does ohmic, or true, resistance have the same effect upon an alternating current as upon a direct current ? A. Yes; in both cases it reduces the current. Q. Is there any inductance with a direct cur- rent? A. No ; as the current is a continuous one, hence there is no reactance or self-induction of the cur- rent. Q. Are inductance and resistance the same? 182 ELECTRIC WIRING. A. No ; the ohmic resistance of a line is the true resistance, arising only from the length of the con- ductor (wire), its cross section and its temperature, while the inductance of the conductor (wire or cir- cuit) arises from the reactance; and hence, is often called by this name. Q. What factors, therefore, limit the free flow of the current? A. The true, or ohmic, resistance of the line, and its reactance. Q. Upon what does the reactance or inductance depend 1 A. Upon the rapidity of the reversals of the cur- rent, the greater the rapidity of the reversals, the greater the inductance. Q. What is impedance? A. It is the sum of all factors opposing a cur- rent; both ohmic and spurious resistances. It is often called apparent resistance or virtual resist- ance. Q. Isfrequency one of the factors of impedence? A. Yes; because the inductance and reactance depends on the frequency, as we have just seen. Q. What is the unit of inductance? A. The henry. Capacity. Q. What is meant by the capacity of a conductor or circuit? A. The relative capacity of a conductor or eir- ELECTRIC WIRING. 183 cuit to retain a charge of electricity with the pro- duction of a given difference of potential. The measure of capacity is the amount of elctricity re- quired to raise the potential (E- M. P.) to a stated amount. The greater the charge required for a given change of potential, the greater the capacity. Q. Upon what does the capacity of a conductor depend? A. Upon its environments, such as the character of the dielectric (insulation) surrounding it; also upon the proximity of oppositely charged bodies, etc. Q. What is the unit of capacity? A. The capacity of a surface which a unit quan- tity will raise to a unit potential. The unit adapted is the surface which a coulomb will raise to one volt, and is called the farad. Q. "What, then, is meant by the capacity of a condenser? A. The quantity of electricity a condenser is capable of holding in coulombs when charged to a pressure of one volt. Q. "What is the effect of capacity on an alternat- ing current? A. In a circuit or system with capacity the cur- rent leads the B. M. P. On the contrary, with in- ductance the E. M- F. leads the current. There- fore, instead of a weak and increasing current, as with inductance, with capacity there is a strong and 184 ELECTRIC WIRING. diminishing current. Inductance produces the ef- fect in a current circuit as though a greater resist- ance were present, while capacity produces the effect as of a less resistance. Inductance and ca- pacity are, therefore, opposed to each other, and tend to destroy each other. Q. By increasing the capacity can the true or ohmic resistance be decreased? A. No; however great the capacity, it cannot decrease the resistance to less than the ohmic re- sistance of the conductor or circuit. Q. By increasing the capacity cannot we entirely destroy the inductance? A. Yes; but it is not practical to do so, and this method of eliminating inductance has never been adopted in practical work. A circuit can, there- fore, be made to contain capacity and no induct- ance, such a circuit being called a capacity circuit. Q. "What is the difference between inductance- reaction and capacity-reaction. A. The first is the reactance of a self-inductive coil, while the second is the reactance of a con- denser. Mutual Induction. Q. What is meant by mutual induction? A. It is the effect produced by the change in the current strength in the conductors of one cir- cuit upon an adjacent circuit. As it is very small in interior wiring, it can be neglected- ELECTRIC WIRING. 185 Skin Effect. Q. What is meant by skin effect? A. When an alternating current is flowing through a conductor, it tends to flow through the outer surface of the conductor; and, therefore, does not utilize the full conductance of the wire. This skin effect is proportional to the frequency of the alternations and the size of the conductor. It there- fore acts in the same manner as an increase in the ohmic resistance; or, as a decrease in the size of the conductor. Lag and Lead. Q. What is lag and lead? A. Lag is where the current falls behind the electro-motive force, due to the self-induction in the magnetizing coils in the circuit. Lead, on the con- trary, is where the current is forced ahead of the electro-motive force, due to capacity being intro- duced into the circuit, as where a condenser, or anything else having electro-static capacity, is in- troduced into the circuit. Q. Explain how self-induction in the magnetiz- ing coils causes the current to lag? A. There can be no current without an electro- motive force, for every current is the effect of the voltage applied to the circuit. If the voltage is an alternating voltage, then the resulting current will be an alternating current, and the current so pro- duced will have the same frequency as the voltage 186 ELECTRIC WIRING. which produced it? Now, should the electro-motive force and resulting current always keep step and travel together, there would be no falling behind of the current, consequently no lag ; but this is not the case, for in almost every alternating circuit there is a certain amount of lag. The lag is caused by the current on its way around the circuit being made to magnetize the electro-magnets which are inserted in its circuit. "While the current rises, the magnetism in these electro-magnets increases ; and as the current dies away, the magnetism in them also decreases. This increasing and decreasing of the magnetism in the circuit sets up self-inductive re- actions, with the result that the current cannot in- crease to its maximum as quickly or as soon as it would do otherwise ; nor can it die away or decrease as quickly and as soon as it would do otherwise, so it is compelled to lag behind the elec- tro-motive force propelling the current- Not only does the self-induction and reactions so produced retard the current, but it chokes or de- creases its strength, so that the current cannot rise to so high a maximum as it would do otherwise. In Pig. 69 is shown the lag of a current behind its electro-motive force or voltage. The full line repre- sents the current curve, and the dotted line the curve of the applied, or impressed, electro-motive force. When the applied electro-motive force is zero, as at Y in Fig. 69-, the current still has a certain ELECTRIC WIRING. 187 — o o a> b >- q-i o an a h-l o CO biD >- fe 188 ELECTRIC WIEING. value and does not become zero until the applied electro-motive force has a value as represented by the vertical line at C. The distance YC represents the lag, which is the same throughout the cycle. Q. How is this distance, or amount of lag, always represented? A. In the degrees of an angle to which it will correspond. For instance, suppose the frequency should be 60 cycles per second ; then one period will last 1/60 of a second. Now suppose the lag was 1/600 of a second behind the voltage, which would be 1/10 of a whole period. As one period is regard- ed as one revolution around the circle, or 360 de- grees the amount of lag therefore would be 36 de- grees. Q. Can a current be so retarded by self-induc- tion as to lag as much as one-quarter of a period, or 90 degrees? A. No ; as can be seen from Fig. 69, and for this reason it is never fully opposed to the applied or impressed, electro-motive force. Q. How much behind the current is always the opposing electro-motive force due to self-induction? A- One-quarter of a period; that is, 90 degrees. Q. What, as we have seen, is this opposing elec- tro-motive force called? A. The inductive, or reactive, elctro-motive force. Q. What is the applied, or impressed, electro- motive force? ELECTRIC WIRING. 189 A. It is the eleeto-motive force supplied by some outside force, as distinguished from the inductive or baclc-eleetro-motive force of the coil. Q. What is the active, or available, electro-mo- tive force? A. It is the electro-motive force available for work. This alone forces the current through the circuit. Q. If the impressed and inductive electro-motive forces were 180 degrees apart, so that they squarely opposed each other, v^ould there be any active or available electro-motive force? A. No ; and hence no current. Q. How is the difference of phase between the two alternating currents described? A. In degrees; the same way in which the amount of lag in a current is described. For ex- ample, suppose an alternator be constructed with two independent coils, marked X and Y, as in Fig. 70, and these two coils be displaced, so that the coil X is a little farther to the right than the coil Y. When the magnet wheel revolves, two independent alternating voltages will be set up in these two coils ; but the voltage in the Y coil will occur a little later than in the X coil, as it is a little farther on in the revolution- As a result, there will be two alter- nating voltages having a difference in phase between them equal to the distance between the X and T 190 ELECTRIC WIRING. Fig. 70. Alternator Coils in Two-Phase. ELECTRIC WIRING. 191 coils, and this difference will be expressed in so many degrees. If Y is displaced from X by an amount equal, say, to one-third of the pitch from one north pole to the next north pole, then Y voltage will lag one-third of a whole period behind the X voltage, so that there will be a difference of 120 degrees between the X voltage and the Y voltage. Q. Suppose the two coils were displaced one-half of the pole-pitch apart, what would then be the difference in phase between the two voltages? A. One-quarter of a period, or 90 degrees, be- cause one coil would always be oije-quarter of a cycle behind the other coil. By referring to Fig. 70 it will be seen that when one of the coils has passed through a quarter of a cycle, the other coil is just beginning its cycle. Q. What is the effect of an increase of self-in- duction upon the lag of a current? A. The more self-induction there is in a circuit, the ^eater becomes the lag of the current behind the electro-motive force. Q. What is such a load which causes little or no self-induction called, such as an incandescent light- ing load? A. A non-inductive load. Q. Does the frequency of a current have any effect on its self-induction? A. Yes; the higher the frequency the greater 192 ELECTRIC WIRING. is the self-induction, as the inductance increases as the rate of change in the strength of a current is increased. Q. Is it possible to neutralize the inductance in a circuit? A. Yes; by hastening the increase and decrease in the strength of the current, thereby causing the current to lead the electro-motive force- Q. How is this effect of lead obtained? A. By use of a condenser in the circuit, thereby increasing the capacity of the circuit. Q. Is it practical to neutralize the inductance, or self-induction, in this way? A. No ; it is not practical, and has never been much adopted as already seen. Power Factor. Q. What is meant by the power factor of a cir- cuit or a device? A. It is the ratio between the true watts and the apparent watts; or the proportion of the ap- parent watts that is available for power. Q. Explain the difference between the true watts and the apparent watts? A. When a current lags and gets out of phase Avith its own voltage, then the full power of the current ceases to be effective. Just so far as the current is out of phase with its electro-motive force, or voltage, does it cease to be effective. We have seen that the power conveyed by a current is equal ELECTRIC WIRING. 193 to the product of the volts and the amperes, pro- vided they act together; but should they not act together, then the product of the volts and am- peres does not give the true number of vpatts, but only the apparent number of watts. This is entirely analogous to a most important principle in mechan- ics, viz. : that the work done by a force in producing a movement is the product of the force into the distance through vphich the body has moved. But this is not true unless the force and the resulting movement are in the same line- If the movement is constrained or takes place at an angle with the force, then the work done is no longer the product of the force, or foot-pounds, and the distance, or feet; but is equal to the product of the apparent number of foot-pounds by the cosine of the angle between the direction of the force and the line of movement. Examples. For instance, if a force equal to the weight of 10 pounds acting obliquely at an angle of 30 de- grees with the line of movement produces a move- ment of 2 feet, the number of foot-pounds of work done will not be 20 feet, since only a component of the force is in the line of movement. The cor- rect result is found by multiplying the 20 foot- pounds by the cosine of the angle 30 degrees, which is 0.866, making the true amount of work done 20+0.866=17.32 foot-pounds. 194 ELECTEIC WIRING. The power of an electric current is found exactly in the same way, as it is only necessary to multiply the apparent watts by the cosine of the angle of lag. For example, if a current of 60 amperes be sent around a circuit by an electro-motive force of 120 volts, and the lag of the current is 40 degrees, the apparent power is 7,200 volt-amperes, or apparent watts. But, since the current lags by an angle of 40 degrees, the true watts, or power, would be 7,200 -i- cosine 40 degrees=7,200 X 0-866 =6235.2 watts. Q. What is the power factor? A. It is the cosine of an angle of lag. Q. What is the rule, then, for finding the correet power of a current? A. The true power is equal to the apparent watts multiplied by the power factor. Q. Name some of the usual lags, with power fac- tors, that are found in practical work. A. For incandescent lighting, the lag varies from 15 to 20 degrees, the power factor being from 96.59 for a lag of 15 degrees to 93.97 for a lag of 20 de- grees. For mixed arc and incandescent lighting, the lag is usually 30 degrees, with a power factor of 86.60; while for small induction motors, it is as large as 60 degrees, the power factor of the same being only 50 degrees. Q. Is there any lag or lead in direct currents? A. No ; only in alternating currents ; therefore, ELECTRIC WIRING 195 in figuring the efficiency of a direct current machine, the power factor is not used. WATTLESS CURRENTS. Q. What is a wattless current? A. We have seen that so fa^ as a current is out of phase with its voltage, just so far is it unable to produce any useful work or to convey any power. Now, if the current is out of phase with its voltage by 90 degrees, it is then acting at right angles to it, and is productive of no useful work or power. Such a voltage is zero, and the current is Wattless. It is a well-known principle in mathematics that a force does no work and spends no energy if it acts at right angles to the line of movement. Every oblique force can be regarded as resolvable into two components — one in line with the motion, and the other at right angles to the motion- The first component is the working component, while the other component is the idle component. So it is with an alternating current. It can always be resolved into two components — the one component in phase with the voltage, the other component at right angles to the voltage. The first component is the working component of the current, and is proportional to the cosine of the angle of lag, while the other component is the idle component. Only when this idle component is at right angles to the current (that is, when the lag of the current is 90 degrees) does it produce no energy and is wattless. 196 ELECTRIC WIRING. It is said, then, to be in quadrature with the volt- age. The idle component is always equal to the sine of the angle of lag. Q. How can we find the value of the whole current from these two components? A. Square each component, add the squares and take the square root of the total. Example. Take a current of 60 amperes with a lag of 40 gderees. We see by reference to Table No. 10, or any similar table made up for this purpose, that the sine of 40 degrees is 0.6428, and that therefore, there will be 64.28 per cent, of idle or useless cur- rent. Now, while our original current was 60 amperes, owing to this idle component, we find that only 45.96 amperes will be available for use- ful work, the remaining 38.56 amperes being idle. The working component can be found by multiply- ing the cosine of 40 degrees, which is 0.7660, by the current, which is 60 amperes, giving a current of 45.96 amperes. Calculation of Alternating Current Circuits. Q. What influences are combined in producing impedance to the free flow of current? A. Three influences, viz. (1) Ohmic or true re- sistance, (2) the reaction due to inductance, and (3) the reactance due to capacity. Q. What is the formula for obtaining imped- ance? ELECTRIC WIRING. 197 Anglo Cosine of Angle Power- factor, in Percen- tages Sine of Angle Idle Cur- rent, in Percen- tages *> 0° 1 100 5° 0-9962 99-62 0-0872 8-72 10° 0-9848 98-48 0-1737 17-37 15° 0-9659 96-59 0-2588 25-88 20°, 0-9397 93-97 0-3420 34-20 25°' 0-9063 90-63 0-4226 42-26 30° 0-8660 86-60 0-5000 50-00 35° 0-8190 81-90 0-5736 57-36 40° 0-7660 76-60 0-6428 64-28 45° 0-7071 70-71 0-7071 70-71 50° 0-6428 64-28 0-7660 76-60 55° 0-5736 57-36 0-8190 81-90 60° 0-5000 50-00 0-8660 86-60 65° 0-4226 42-26 0-9063 90-63 70° 0-3420 34-20 0-9397 93-97 75° 0-2588 25-88 0-9659 96-59 80° 0-1737 17-37 0-9848 98-48 85° 0-0872 8-72 0-9962 99-62 90' 0-000 0-00 1-000 100 , — ,^ — -.^ Table No. 10. Sine, Cosine and Power Factors. 198 ELECTRIC WIRING. A. Impedance=\/Ohiiis °+ (Inductive reactance — ■"/Capacity reactance)\ Example. Q. Suppose the resistance of the circuit = 5 ohms, the inductive reactance = 50 and the ca- pacity reactance = 25, then we would have Impedance=\/5X5+(50— 25)'. =V650 = 25.49. We see from this that, while the circuit has only 50 ohms resistance due to the wire itself, the reactance of the current increases its apparent resistance to 25.49. Therefore, with high inductance and low resist- ance, the true or ohmic resistance becomes unim- portant, and in many cases can be altogether neg- lected. Q. In wiring calculations where an alternating current is used, what must first be determined ? A. The actual current which will flow in the line. This is done by computing the current that would flow according to direct current laws, and then divide by the power factor and multiply by 100. This will give the current. Q. Is it necessary to determine the impedance to the flow of the current so found 1 A. Yes; to determine the impedance, divide the drop (volt loss) allowed for the line, by the cur- rent as above found, which gives the total imped- ance for the line. To find the impedance per foot, it is only necessary to divide the total impedance ELECTRIC WIRING.. 199 by the length of the line (single distance), which will give the impedance per loop foot- Q. Does the character of. the current have any effect on the size of the wire? A. Yes; in alternating current work the wire should be larger than when direct current is used. Q. Does the frequency effect the size of the wire to be used? A. Yes; the greater the frequency, the larger must be the size of the wire used. Q. Does the phase of the current also effect the size of the wire used? A. Yes; the size varies according to whether single, two, or three phase circuits are used. Q. Give a formula for finding the size of wire in circular mils for alternating current mains. DXWXC A. Circular mils ^ PXE^. in which formula W=watts delivered; D^length of run; p^line loss in power delivered; E=volts between receiving end of circuit. C=2,160 for direct current. Q. What is one of the first elements to be con- sidered in the calculation of alternating circuits? A- The power factor. Q. Why is this so? A. As we have already seen, in all alternating 200 ELECTRIC WIRING. current measurements we have two phenomena, viz., the real power and the apparent power. To express the ratio between these two elements, the term power factor is used. The power factor therefore is a fraction by which we must multiply the apparent watts to obtain the true or useful watts, as has been explained. Q. If we multiply the volts as shown by a volt- meter by the amperes as shown by an ammeter, do we get apparent or true watts? A. Apparent watts, and to find the useful watts (power) we must multiply their product by the power factor, which power factor is usually ob- tained from tables. Q. We have seen that with direct current, W= ExC; if it should happen that there were no in- ductance in a circuit, could not this formula be also used for an alternating current ? A. Yes; but this rarely happens, as in an alter- nating current there is usually some difference or lag between the current and the electro-motive force. On the contrary, with a direct current there is no ditference in phase betwen the current and the electro-motive force. Q. What is the formula for finding the power of alternating currents? W=C'XR, or W== -^j- Q. Does a wattmeter show the apparent power (watts), or the useful and effective power (watts) ? ELECTEIC WIRING. 201 A. The useful and effective power (watts). "Were this not the case, this instrument would not be of much practical value, as it would not give the effective load. Q. As the power factor depends upon the induct- ance in the circuit, suppose the load is incandescent lamps, or similar non-inductive appliances, making a non-inductive load, what would be the power factor ? A. Almost unity, that is, about 96 per cent (.96), as already explained. Q. In calculating the size of conductors to be used for a given load, must the apparent or the effective current be used? A. The apparent current. Q. Where the actual load is given, how do we find the apparent loads in watts? A. Simply divide the actual load by the power factor, which will give the apparent load in watts. Should only the actual load be allowed for, then the conductors and generators would not be large enough to carry the apparent load- Q. As the difference between the actual load and apparent load does not effect the actual load on the engine, why should it effect the load oh the generator? A. The power supplied by the engine is the same in both cases, but the current supplied to the gen- erator gives both an effective power find an appar- 202 ELECTRIC WIRING. ent power, as we have already seen. It is the power which is not actually used, corresponding to the apparent watts, which heats the conductors and generators; and, therefore, their size must be in- creased so as to allow for this wattless current. Therefore, an allowance must be made for the power factor of the apparatus. Q. How is the power factor of an apparatus ob- tained ? A. Usually from the manufacturer of same. Q. How is the current in the conductors found for different phase circuits? A. By using the following formula: For single phase circuit : W C== EXP- F. For two phase circuit: W C = 5X EXP. F. For three phase circuit : W C = 58X EXP- F. in which formulas C = current in amperes ; "W = the watts ; E = the voltage ; and P. F. = the power factor of the circuit. ELECTRIC WIRING. 203 CHAPTER XIII. Overhead Line Work. Q. In what two classes can overhead line work be divided? A. Into long transmission lines, employiiig high potential circuits, and into industrial plant work, employing low potential circuits. Q. How must the conductors used in overhead line work in industrial plants be protected? A. They must have double-braided weather-proof insulation. Q. Why are transformers which are connected to high voltage circuits required to be placed out- side of all buildings, excepting central stations and substations ? A. In order to keep the high voltage primary wires entirely out of the building thereby, avoiding the dangers from fire and personal injury. Q. How are the poles supporting the wires spaced? A. The poles should be set about 120 feet apart. Q. What are the requirements for poles? A. They should be of a selected quality of cedar or chestnut, and should be sound and free from knots and cheeks. Q. What size poles are used for ordinary over- head work? A. Poles from 25 to 30 feet in length, and at the smaller end of not less than 6 or 7 inches. Q. Before erecting the poles how should they be treated ? 204 ELECTRIC WIRING. A. The butt end should be tarred or creosoted, so as to prevent decay. The poles should all be shaved and cleaned, ready for painting before erect- ing. Q. How should all poles be set? A- They should be set to a depth of from 5 to 8 feet in the ground, depending on the length of the pole and the character of the soil. They should be set perpendicular, except when it is necessary to "rake" them. Q. What is meant by "raking" a pole? A. To incline the pole in order to withstand an extra strain in any direction. Q. What is meant by the gains? A. The spaces cut in the faces of the poles for the support and placing of the cross-arms. Q. How large should the gains be cut in the poles? A. About 11/2 inches deep and about 4% wide, so as to closely fit the cross-arms. Q. What are the cross-arms? A. The horizontal beams attached to the pole for the support of the insulators. Q. Describe the cross arm used in ordinary work- A. They should be made of a high-grade Michi- gan or Norway pine, and thoroughly seasoned. Their length depends on the number of pins that they are to carry. For three pins, the arms should not be less than 36 inches in length, and not less than 48 inches in length for four pins ; and should be about 3% by ^% inches in width and thickness. ELECTRIC WIRING. 205 Q. How are the cross-arms fastened to the poles? A. With iron lag screws about 7 inches long and 5/8 inches in diameter. The number of lag screws to be used depends on the number of pins, usually two lag screws being allowed for each pin. Q. How are the ping made? A. Of selected locust, being made about 1^2 inches in diameter. They are fitted in the cross- arms and then nailed in place. Q. What character of insulators are used for in- dustrial plant work? A- As such plants are low potential circuits, the insulators are of glass, and usually of the double "petticoat" type, such as shown in Fig. 71. Q. What type of insulators are used for high potential circuits? A. Such as shown in Figs. 72 and 73. Q. How should the conductors (wires) be guarded? A. Guard irons should be used at all turns and corners to prevent the wires from dropping to the ground in case they should become detached from the insulator or the cross-arms. Underground Line Work. Q. What is meant by an underground conductor ? A. An electric conductor insulated and placed under the surface of the earth. Q. Is it preferable to run the conductors under- ground to overhead? 206 ELECTRIC WIRING. Fig. 71. Double Petticoat Insulator. Pig. 73. Tripple Petticoat Insulator. ELECTRJC AVIRIXr}. 207 Fig. 73. High Potential Insulator. 208 ELECTRIC WIRING. A. Yes, especially when the circuits carry high potentials, or when the wires are liable to overhead disturbance- Overhead wires are, also, very un- sightly and often very much in the way, as in ease of fires, etc. Q. "Why, then, are not all conductors run under- ground ? A. On account of the cost, which is considerably greater than when the wires are strung overhead. Q. "Why is the cost so much greater? A. For two reasons, viz., (1) The cost of the con- duits and installation is much greater than the cost of the poles and stringing of the wire, but (2) The cost of the conductors for underground work is much greater than conductors for overhead work. This is owing to the necessity of using only rubber- insulated and lead-enclosed conductors for under- ground work, while for overhead work only weather- proof insulation is required. Q. In all underground work what is the first consideration? A. An arrangement permitting the conductors to be easily removed and replaced without disturb- ing the conduits or ducts. Q. Is there any difference between a conduit and a duet? A. Yes; the conduit is the underground space, while each one of the separate spaces into which this space is divided is called a duct. ELECTRIC WIRING. 209 Q. What methods are now in general use, permit- ting free access to the conductors ? A- There are four principal methods now in gen- eral use for underground work, viz. : (1) Iron pipe conduits; (2) Wood conduits; (3) Fiber conduits; (4) Vitrified conduits. IRON PIPE CONDUITS. Q. Describe an iron pipe conduit. A. This conduit is generally used only for short lengths of small conductors, in places where the soil is loose and liable to "cave in-" Q. How is the conduit laid? A. Simply placed in a trench, but when more than one conduit is to be run in the trench, then be laid in a bed of concrete about two or three inches thick. WOOD CONDUITS. Q. Describe a wood conduit. A. This conduit is now not much used, owing to it being liable to injury from pick or shovel, requir- ing it to be laid at a considerable distance under- ground, and often requiring an additional partition, such as a covering of plank, etc. These conduits are usually made about 8 or 9 feet in length, with about a 3 or 4-inch square opening in same. In order to preserve the wood, they are 210 ELECTRIC WIRING. impregnated with coal tar, or some similar wood preservative- FIBER CONDUITS. Q. Describe a fiber conduit. A. This is a widely used form of conduit for underground work. It is usually made by wrapping wot wood pulp or fiber upon a mandrel under a high pressure. After the tube is so formed, it is removed thoroughly dried, and placed in a tank of preserva- tive and insulating compound. Q. Into what types are fiber conduits usually made ? A. Into three types, viz. (1) The socket-joint type. (2) The sleeve-joint type, shown in Fig. 75; (3) The screw-joint type, shown in Fig. 76. Q. Which of these three types is most generally used? A. The screw-joint type. Q. What is the objection to the socket-joint type? A. When this type of conduit is used, the lengths of the conduit must be held rigidly in position, which requires the conduit to be laid in cement. Q. Describe the construction of the screw-joint type of this conduit. A. The ends of the conduit are threaded, and the sleeve which fits over the ends is also threaded, so instead of slipping the sleeve over the ends as with ELECTRIC WIRING. ■211 Fig. 73. Sleeve Joint Fil)er Conduit. Fig. 76. Screw Joint Fiber Conduit. Fig. 77 (1). Clay Conduit. Single and Multiple Ducts. 212 ELECTEIC WIEING. the sleeve joint type, it is screwed on, giving a much more secure joint. Q. What are the disadvantages of fiber conduits? A. Owing to its lightness and material of which it is composed, it is not mechanically strong. It, there- fore, requires a good, strong foundation ; and, in all cases should be laid in a concrete bed of at least two inches thickness. Q. Describe a vitrified conduit. A. This form of conduit is generally used where a number of conductors are to be laid in the same trench. The conduit is constructed with from one to a dozen ducts in which the separate conductors are placed, the ducts being made either round or square. Q. What is the advantages of making the ducts square? A. It gives a larger area than a round duct, and, thereby, permits more conductors to be placed in each duct; and at the same time decrease the re- sistance to the conductors when drawn through the duct. Q. What are the advantages of vitrified conduits ? A. They are inexpensive and practically inde- structible. At the same time they are mechanically strong, and a good insulator for low potentials. They are easily installed, and made up in a great variety of forms. Like fiber conduits, they should ELECTRIC WIRING. 213 always be laid in a bed of concrete at least two inches thick. CODE REQUIREMENTS. CONSTANT-CURRENT SYSTEMS. Principally Series Arc Lighting. 18. Wires. a. Must have an approved rubber insulating cov- ering. C. Must always be in plain sight, and never en- cased, except when required by the Inspection De- partment having jurisdiction. d. Must be supported on glass or porcelain insul- ators, which separate the wire at least one inch from the surface wired over and must be kept rigidly at least eight inches from each other, except within the structure of lamps, on hanger-boards or in cut-out boxes, or like places, where a less disr tance is necessary. e. Must, on side walls, be protected from mechan- ical injury by a substantial boxing, retaining an air space of one inch around the conductors, closed at the top (the wires passing through bushed holes), and extending not less than seven feet from the fljor- "When crossing floor timbers in cellars, or in rooms where they might be exposed to injury, wires must be attached by their insulating supports to the under side of a wooden strip not less than one-half 214 ELECTRIC WIRING. an inch in thickness. Instead of tho running-boards, guard strips on each side of and close to the wires will be accepted. These strips to be not less than seven-eighths of an inch in thickness and at least as high as the insulators. 19. Series Arc Lamps. a. Must be carefully isolated from inflammable material. b. Must be provided at all times with a glass globe surrounding the arc, and securely fastened upon a closed base. Broken or cracked globes must not be used. c. Must be provided with a wire netting (having a mesh not exceeding one and one-fourth inches) around the globe, and an approved spark arrester when readily inflammable material is in the vicin- ity of the lamps, to prevent escape of sparks of carbon or melted copper. d. Where hanger-boards are not used, lamps must be placed out of reach or suitably protected. "Enclosed arc" lamps, having tight inner globes, may be used, and the requirements of Sections b and C above would, of course, not apply to them. d. Where hanger-boards are not used, lamps must be hung from insulating supports other than their conductors. e. Lamps when arranged to be raised and lowered, either for carboning-or other purposes, shall be con- ELECTRIC WIRING. 215 nected up with stranded conductors from last point of support to the lamp, when such conductor is larger than No. 14 B. & S. gage. 20. Incandescent Lamps in Series Circuits: a. Must have the conductors installed as required in No. 18, and each lamp must be provided with an automatic cut-out. b. Must have each lamp suspended from a hanger- board by means of rigid tube. 0. No electro-magnetic device for switches and no multiple-series or series-multiple system of lighting will be approved. d. Must not under any circumstances be attached to gas fixtures. 15 Underground Conductors. a. Must be protected against moisture and me- chanical injury where brought into a building, and all combustible material must be kept from the immediate vicinity. b. Must not be so arranged as to shunt the cur- rent through a building around any catch-box. c. Where underground service enters building through tubes, the tubes shall be tightly closed at outlets with asphaltum or other non-conductor, to prevent gases from entering the building through such channels. d- No underground service from a subway to a building shall supply n).ore than one building except 216 ELECTRIC WIRING. by written permission from the Inspection Depart- ment having jurisdiction- Trolley Wires. j. Must not be smaller than No. B. & S. gage copper or No. 4 B. & S. gage silicon bronze, and must readily stand the strain put upon them when in use. k. Must have a double insulation from the ground. In wooden pole construction the pole will be consid- ered as one insulation. 1- Must be capable of being disconnected at the pcnver plant, or of being divided into sections, so that in case of fire on the railway route, the current may be shut off from the particular section and not interfere with the work of the firemen. This rule also applies to feeders. m. Must be safely protected against accidental contact where crossed by other conductors. Where guard wires are used they must be insu- lated from the ground and electrically disconnected in sections of not more than 300 feet in length. Ground Return Wires. n. For the diminution of electrolytic corrosion of underground metal work, ground return wires must be so arranged that the difference of potential between the grounded dynamo terminal and any point on the return circuit will not exceed twenty- five volts. 13. Transformers. ELECTRIC WIRING. 217 a. Must not be placed inside of any building, ex- cepting central stations and substations (except as provided in No. 30 A), unless by special permission of the Inspection Department having jurisdiction. b. Must not be attached to the outside vpalls of buildings, unless separated therefrom by substantial supports. Must not be attached to frame buildings when any other location is practicable. 218 ELECTRIC WIRING. CHAPTER XIV. Testing, Q. What is the usual object in testing circuits ? A. To discover and remove faults or troubles. Q. What are the most usual and serious troubles in circuits? A. Short circuits and grounds. Q. What usually causes short circuits? A. The crossing or touching of wires. Q. What usually causes grounds? A. The wire coming in contact with gas or water pipes. Q. What is a ground? A. The contact of a conductor of an electric circuit with the earth, or with some conductor lead- ing to the earth, such as a gas or water pipe. Q. How does a short circuit usually show itself? A. By the fuses blowing. Q. How are heavy grounds detected? Faraday's Dynamo. ELECTRIC WIRING. 219 A. By ground detectors, which are mounted on the switchboard. Q. Describe the principle of such a ground de- tector for a two-wire and a three-wire system- A. In Fig. 77 is shown the arrangement of the ground detector for a two wire system. Two lamps are connected in series across the two main lines or legs. The connecting wire between the two lamps A and B is grounded by connecting it with a gas or water pipe. When both wires are free from grounds, the lamps (A B) burn with equal brightness, but if there is a ground on one leg of the circuit, then the lamp connected to the other leg burns more brightly. For instance, should the lamp (A) burn brighter than the lamp (B) then the ground is in the lower or negative leg of the circuit. The switch shown in the cut must always be left open, except when the line is to be tested. In Pig. 78 is shown the arrangement used for a three-wire system. In this sjstem, should a ground occur on the positive wire, the lamp connected to the neutral wire will burn brighter than the other lamp. In the same way, if a ground occurs either on the neutral or negative wire, the lamp on either the neutral or the negative wire will burn brighter than the other lamp. Q. What precaution must be used in testing out a three-wire system? 220 ELECTRIC WIRING. I t A 5. ¥ <> ground: Fig. 77. Ground Detector for Two-Wire System. ELECTEIC WIRING. 221 A. Never close the two switches (B F) at the same time. If this is done, it will cause a short circuit, because both of the outer legs will then have to carry the entire current. Therefore, only one switch must be closed at a time ; and, after test- ing that side of the circuit, open the switch and close the other switch to test the other side- Q. Instead of using lamps for testing, could not a voltmeter be used ? A. Yes; the principle being just the same. The wire which gives a reading indicates that the other wire is grounded. GROUNDS. Q. Does the current always escape when there is a ground? A. No ; only when there are two grounds. Q. What is meant by a ground return? A. It is where the ground or earth is used for part of an electric circuit, as in telegraphy. Q. What is a partial ground ? A. A single ground. Q. Does a partial or single ground on a machine impair its action? A. No; it only renders the insulation in some part of the machine liable to break down. Q. Is this the case when there are two grounds on a machine? A. No ; as this would cause a short-circuit through the winding of the machine, probably burning the 222 ELECTRIC "WIRING. i A A i ilA i o i H i ? i ? ^ -u. + N. C. D. UP fin () () I Fig. 78. Ground Detector for Three-Wire System. ELECTRIC WIRING. 223 insulation and stopping the operation of the ma- chine. Q. How may grounds be classed? A. Into three classes : (1) High resistance grounds; (2) Low resistance grounds; (3) Dead grounds. Q. Describe each class. A. A high resistance ground is uusally several thousand ohms, a low resistance ground is several hundred ohms; while a dead ground is a direct contact betwen a wire and the earth, as through a gas or water pipe. THE MAGNETO. Q. How is the testing for grounds usually done ? A. By means of a small dynamo, which is pro- vided with a field made of permanent magnets and operated by hand. Such an instrument is called a magneto. When current passes through the cir- cuit, its presence is indicated by the ringing of a pair of small bells attached to the device. Q. How is the magneto connected for testing a circuit ? A. One wire from the magneto is grounded by connecting to a gas or water pipe, while the other wire is connected to each wire of the circuit to be tested in turn. In Fig. 79 is shown the construction of a magneto. If the magneto rings, it indicates a ground, the circuit then being a closed circuit. 224 ELECTKIC WIRING. Fig. 79. A Magneto. ELECTRIC WIRING. 225 If, on the contrary, the magneto does not ring, no ground is present on the line being tested, as the circuit in that event is open. Q. Is this a very reliable method of testing for grounds ? A. No; since the alternating current produced by the magneto may in itself sufficiently charge an ungrounded line as to cause it to ring the bell. Again, the insulation may provide certain electro- static conditions, causing the magneto to receive a return static charge from the ungrounded v?ire, sufficiently great to ring the bell. Q. Can a line with a resistance of 5,000 ohms be tested with a magneto which will ring only through a resistance not exceeding 4,000 ohms? A. No; therefore, magnetos are constructed so as to ring through different resistances depending on the resistance of the line to be tested. The maximum resistance through which a mag- neto will ring is marked on the instrument, and it can be used only for such resistance or less. A ground which can be rimg through by a mag- neto is, therefore, of the same resistance as the instrument, or less. In this way a magneto can be used for measuring the resistance of a line, though not very accurately. Q. Can a magneto be used for detecting the ground in a heavy wound coil, such as the fivilds of a generator ? 226 ELECTRIC WIRING. A. No ; since the rapid reversals of the alternat- ing current from a magneto, could not penetrate the numerous windings of the coil, due to the self- induction which would be produced. Q. If there is a break in the line, how is this known ? A. The magneto will not ring, as the current is then open. Lightning Arresters. Q. What is a lightning arrester ? A. A device to protect the apparatus in an elec- tric circuit from the destructive discharge of light- ning. Q. How is this done? A. The discharge is carried off to earth, thus rendering it harmless. Q. Are lightning arresters employed for both alternating and direct current circuits? A. Yes; since such circuits attract equally all lightning discharges. Q. What injuries are usually caused to circuits by a lightning discharge ? A. Short circuits and grounds. Q. How does lightning arresters afford protection against such injuries ? A. The lightning arrester is so constructed as to prevent a sudden rise of potential in the lines. Q. How is this done ? A. By using an air gap, and a dead ^ound. In ELECTRIC WIRING. 227 Pig. 80 is shown the principle of the lightning arrester in which the space A is the air gap. The lines have a. plate with teeth connected to them; a second similar plate is placed near this plate with teeth opposite to those of the first plate, and nearly touching it. While the ordinary voltage carried by the line is not sufficient to cause it to jump across this air gap, any sudden rise of the potential caused by the lightning discharge is suffi- ciently great to jump across this gap, where it is carried to earth, thus rendering it harmless. Q. Instead of using the air gap as an insulator, could not some kind of insulation with a very high resistance be used? A. Yes; the two plates are often placed face to face, and between them paper or mica is pressed. While the ordinary voltage of the line will not pierce this insulation, a lightning discharge will do so, and be carried to the earth harmless as be- fore. In Pig. 81 is shown an ordinary type of light- ning arrester. Q. Where no lightning arresters are used, what ordinarily takes place wheri the lightning strikes a station. A. An arc is developed betwen the wires of opposite polarity, and this arc is apt to cause a fire or personal injury. 228 ELECTEIC WIRING. LINE Fig. 80. Principle of the Lightning Arrester. ELECTRIC WIRING. 229 Q. Where is the lightning arrester usually placed? A. Near the end of the line before it reaches any instrument; in power plants, usually where the wires enter the buildings; and, also, at the switch- board to prevent injury not only to the apparatus but to the operators of the plant. CODE REQUIREMENTS. 13A. Grounding Low-Potential Circuits. Ground Connections. c. When the ground connection is inside of any building, or the ground wire is inside of, or attached to any building (except Central or Sub-stations) the ground wire must be of copper and have an approved rubber insulating covering National Elec- trical Code Standard, of from to 600 volts. d. The ground wire in direct-current 3-wire sys- tems must not at Central Stations be smaller than the neutral wire and not smaller than No. 4 B. & S. gage elsewhere. The ground wire in alternating current systems must never be less than No. 4 E. & S. gage. On three-phase system, the ground wire rriust have a carrying capacity equal to that of any of the three mains. e. The ground wire should, except for Central Stations and transformer sub-stations, be kept out- side of buildings as far as practicable, but may be directly attached to the building or pole by cleats or straps or on porcelain knobs. Staples must never 230 ELEL'TiaC WIIMXG. Fig. 81. Ordinary Type , 243 ,£3 ft bo ^ U >1 S; 05 ^ CO ^; bo ^"> N -^=Hl-° — ^ 244 ELECTKIC WIRING. '■+J 03 +-> o 03 6C ELECTRIC WIRING. 245 CODE REQUIREMENTS. Wireless Telegraph Apparatus. In setting up wireless telegraph apparatus, all wir- ing within the building must conform to the Rules and Requirements of the National Board of Fire Un- derwriters governing the class of work installed and to the following additional rules: AERIAL WIRE: Aerial conductor must be at least No. 8 B. & S. gauge rubber covered wire run on petticoat insul- ators or exterior of building, and on knobs, cleats, or in moulding in interior of building. Porcelain Bushings to be used through walls, partitions and floors. GROUNDING: a. Aerial conductor must be permanently and ef- fectively grounded, at all times when station is not in operation, by a conductor not smaller than No. 4 B. & S. gauge rubber covered copper wire run as nearly in a straight line as possible to a water pipe at a point on the street side of all connections of said water pipe within the premises, or to some other equally satisfactory artificial earth connection, such as an iron rod or pipe driven at least 5 feet into the earth. Ground wire should be protected from me- chanical injury by enclosing it in moulding at least 7 feet from the ground on exterior of building. The switch employed to join the aerial to the ground 246 ELECTRIC WIRING. connection must be an approved 100 ampere, single ampere, single pole, double throw knife switch placed as nearly as possible to where aerial enters and must effectively cut off all apparatus within the building. b. Aerial conductor must be permanently con- nected at times to earth through an approved light- ening arrester placed as nearly as possible to the point where the wire enters the building and groun- ded as specified above. SENDING END : If source of generating current is taken from lightening circuit (10 volts or over) such wiring must be installed in accordance with the Rules and Requirements of the The National Electrical Code. NOTE : Notice of wiring done for these installa- tions should be sent to the Chicago Board of Under- writers as is done for other electrical work. ELECTRIC WIRING. 247 ELECTRIC RAILWAYS. Surface Railways — Electric Railways — Interurban Railways. Q. How are electric cars propelled? A. By electric motors. Q. How is the current which drives the motors supplied? A. In two ways, viz., (1) By an accumulator car- ried with the car, such as storage batteries; or, (2) From mechanical driven generators outside of the car. The first method is now but rarely used owing to its expense and inconvenience. Systems of Di.'stributlon. Q. How may the line system which supplies the 248 ELECTRIC WIRING. current to the motors from the electric generators be divided? A. Into three divisions: 1. The trolley, or overhead system, embracing the third- rail system. 2. The underground system. 3. The surface system. Q. "Which of these systems is at present most used? A. The trolley or overhead system, in which an overhead trolley wire is the conducting medium. Q. When is a third rail used ? A. While the trolley system is still an excellent method of secondary distribution for city service and interurban roads, the demand for a greater power that can be collected from a suspended copper conductor has lead to the introduction of the third rail, the third rail taking the place of the trolley wire as the conducting medium. Q. What horse power can be satisfactorily fur- nished when a trolley wire is used as the conducting medium- A. Only from 200 to 300 H. P., while a third rail can supply as high as 4,000 H. P., though this high power at present is rarely used- Q. In what work is the third rail at present mostly use ? A. In operating c4evated or overhead roads, and ELECTRIC WIRING. 249 in heavy freight hauling on railroads and railway terminals. Q. What is the objection to the underground system 1 A. It is too expensive, and is exceedingly diffi- cult to repair in case of damage. Q. What is the objection to the surface system? A. As the rails themselves are used as the con- ducting medium, it renders such a system both unsafe and impractical. Q. Of what does an ordinary trolley or overhead system consist? A. In a single trolley system the inechanism con- sists of the following well-known parts, viz., the trolley wheel, the trolley pole, the trolley base, and the trolley rope. In Fig. 91 is shown a bracket sup- port of trolley wire for double-track railway. Q. Describe the operation of a trolley system? A. The current is taken from the generator to the switch board and thence directly to the trolley wire. In Pig. 28 is shown the path of the current. So much of the current is taken 'by each car as re- quired for its operation, such portion of the current passing down through the trollej^ pole to the mo- tors in the car; and, thence, through the motors to the rails, where it flows back to the generator, thus making a complete circuit. In Fig. 28 is shown the path of the complete circuit. The trolley pole is mounted at its lower end on 250 ELECTRIC WIRING. Fig. 91. A Bracket Support of Trolley Wiro for Double-track Railway. ELECTRIC WIRING. 251 a trolley frame or base, such as shown in Fig. 28. The spring exerts a pull against the trolley pole, thereby holding the trolley wheel firmly against the overhead wire. Q. How is the third rail system operated? A. A third rail is placed between or on the side of the regular tracks, and a cast iron contact shoe is employed to make travelling contact in order to take the current from the rail as the shoe is carried along by the movement of the car. Q. In this system what is employed as the return circuit ? A. The regular tracks. Q. What voltage is generally employed for oper- ating electric cars? A. 550 or 600 volts. Q. What size trolley wire is generally used? A- No. hard drawn copper wire (American gauge), it being 32-100 of an inch in diameter. Q. What are "feeder" wires? A. In order to decrease the amount of wire used in trolley conductors a system of "feeders" is nec- essary. Such a system is shown in Fig. 28. Sep- arate conductors, S'^, S^, S^, S*, are connected with the trolley wire at different distances from the power house. The current required to supply the car C shown in Fig. 28 is furnished mainly by the feeder GS^, the other "feeders" being comparativ- ely idle so far as the current supplying this car. 252 ELECTRIC WIRING. Q. What other advantage has this system of trol- ley feeders? A. Should the trolley wire break, it would not put all the cars out of operation, but only those cars on the broken circuit. In many instances even those cars can be kept in operation by shunting them across the broken circuit. Q. Since the rails are used for the return circuit, is it not necessary to reduce the resistance of this circuit at the end breaks of the contiguous rails? A. Yes, and various methods are used for this purpose. Usually the ends of the rails are joined or tied together by means of copper wires, called "bonding"; the two tracks also being connected by such wires. In all strictly modern work, instead of the ends of the rails being "bonded" by wires, they are welded together. This is done by passing a powerful electric current between the ends of the rails sufficient to raise them to a welding temper- ature, and pieces of iron, called chucks, placed be- tween the rails are at the same time so heated by the passage of the current that they become welded to the rail, the whole forming one continuous piece, giving practically a complete, unbroken metallic return circuit for the current. Q. What other advantage has a good "bonding" system ? A. It prevents the leakage of current, which ELECTRIC WIRING. 253 leakage causes electrolytic corrosion of the neigh- boring gas and water pipes. Q. How is the current that is used to heat and light the ear obtained? A. From the trolley wire. As the current has a pressure of 550 volts, the lamps must be con- nected in series with the trolley wire and the track, being connected across the same. The number of lamps depends on the voltage of the lamps. Motor Work of Factories. Q. Why is the use of motors for driving machin- ery increasing so fast? A. Owing to their ease of installation, and as they can be directly coupled to the driving shaft of the machine which they are intended to operate, all use of belting and shafting is avoided. This greatly decreases the mechanical loss due to the fric- tion of the belting and shafting, and at the same time gives more space for air and light. When the speed of the motor is too great to per- mit it to be directly coupled to the shafting, suitable gear wheels are employed for reducing the speed. Q. Can motors be operated either on constant current or constant potential systems? A. Yes. In Fig. 92 is shown a Motor Starter as used in or- dinary circuits. CODE REQUIREMENTS. Motors. Where the circuit-breaking device on the motor- 2rA ELECTKIC WIKING. Fig. 92. Motor Starter, ELECTRIC WIRING. 255 starting rheostat disconnects all wires of the cir- cuit, the switch called for in this section may be oiliitted. Overload-release devices on motor-starting rheo- stats will not be considered to take the place of the cut-out required by this section if they are inoper- ative during the starting of the motor. An automatic cireuitbreaker disconnecting all wires of the circuit may, however, serve as both switch and cut-out. Auto starters, unless equipped with tight cas- ings enclosing all current-carrying parts, in all wet, dusty or linty places, must be enclosed in dust- tight, fireproof cabinets. Where there is any lia- bility of short circuits across their exposed live parts being caused by accidental contacts, a rail- ing must be erected around them. e. Must not be run in series-multiple or multiple- series, except on constant potential systems, and then only by special permission of the Inspection Depart- ment having jurisdiction. f. Must be covered with a water-proof cover when not in use, and, if deemed necessary by the In- spection Department having jurisdiction, must be enclosed in an approved case. Such enclosure must be readily accessible, dust- proof and sufficiently ventilated to prevent an ex- cessive rise of temperature. Where practicable, the 256 ELECTRIC WIRING. sides should be made largely of glass, so that the motor may be always plainly visible. The use of enclosed type motor is recommended in dusty places, being preferable to wooden boxing. g. Must, when combined with ceiling fans, be hung from insulated hooks, or else there must be an insulator interposed between the motor and its support. h. Must each be provided with a name-plate, giv- ing the maker's name, the capacity in volts and am- peres, and the normal speed in revolutions per min- ute. i. Terminal blocks when used on motors must be made of approved non-combustible, non-absorptive, insulating material such as slate, marble or porce- lain. j. Adjustable speed motors, unless of special and appropriate design, if controlled by means of field regulation, must be so arranged and connected that they cannot be started under weakened field. 8. Motors. a- Must, when operating at a potential in excess of 550 volts, have no exposed live metal parts, and have their base frames permanently and effectively grounded. i Motors operating at a potential of 550 volts or less must be thoroughly insulated from the ground wherever feasible. Wooden base frames used for this purpose, and wooden floors, which are depended ELECTEIC WIRIXG. 25? upon for insulation where, for anj' reason, it is necessary to omit the base frames, musi: be kept filled to prevent absorption of moisture, and must be kept clean and dry. Where frame insulation is impracticable, the Inspection Department having jurisdiction may, in writing, permit its omission, in which ease the frame must be permanently and ef- fectively grounded. b. Motors operating at a potential of 550 volts or less must be wired with the same precautions as required by rules in Class "C" for wires carrying a current of the sam-e volume. Motors operating at a potential between 550 and 3,500 volts must be wired with approved multiple conductor, metal sheathed cable in approved un- lined metal conduit firmly secured in place. The metal sheath must be permanently and effectively grounded, and the construction and installation of the conduit must conform to rules for interior con- duits (see No. 25), except that at outlets approved outlet bushing shall be used. The motor leads of branch circuits must be de- signed to carry a current at least 25 per cent, greater than that for which the motor is rated. Where the wires under this rule would be over- fused in order to provide for the starting current, as in the case of many of the alternating current motors, the wires must be of such size as to be properly protected by these larger fuses. 258 ELECTRIC WIRING. LOW POTENTIAL SYSTEMS. 550 Volts or Less. Any circuit attached to any machine, or combina- tion of machines, which develops a difference of potential between any two wires, of over ten volts and less than 550 volts, shall be considered as a low-potential circuit and as coming under this class, unless an approved transforming device is used, which cuts the difference of potential down to ten volts or less. The primary circuit not to exceed a potential of 3,500 volts unless the primary wires are installed in accordance with the requirements as given in No. 12 A, or are underground. For 550 volt motor equipments a margin of ten per cent, above the 550 volt limit will be allowed at the gen- erator or transformer. HIGH-POTENTIAL SYSTEMS. 550 to 3,500 Volts. Any circuit attached to any machine or combina- tion of machines which develops a difference of potential between any two wires, of over 550 volts and less than 3,500 volts, shall be considered as a high-potential circuit, and as coming under that class, unless an approved transforming device is used, which cuts the difference of potential down to 550 volts or less. For 550 volt motor equipments a margin of ten per cent, above the 550 volt limit will be allowed at the generator or transformer without coming under high-potential systems. ELECTRIC WIRING. 259 35. Wires. a. Must have an approved rubber-insulating cov- ering. b. Must be always in plain sight and never en- cased, except as provided for in No. 8 b, or where required by the Inspection Department having juris- diction. c- Must (except as provided for in No. 8 b), be rigidly supported on glass or porcelain insulators, which raise the wire at least one inch from the surfaces wired over, and niust be kept abotit eight inches apart. Rigid supporting requires under ordinary con- ditions, where wiring along flat surfaces, supports at least about every four and one-half feet. If the wires are unusually liable to be disturbed, the dis- tance between supports must be shortened. In buildings of mill construction, mains of not less than No. 8 B. & S. gage, where not liable to be disturbed, may be separated about ten inches and run from timber to timber, not breaking around, and may be supported at each timber only. d. Must be protected on side walls from mechan- ical injury by a substantial boxing, retaining an air space of one inch around the conductors, closed at the top (the wires passing through bushed holes) and extending not less than seven feet from the floor. 260 ELECTRIC WIRING. 36, Transformers. Transformers must not be placed inside of build- ings without special permission. a. Must be located as near as possible to the point at which the primary wires enter the building. b. Must be placed in an enclosure constructed of fire-resisting material; the enclosure to be used only for this purpose, and to be kept securely locked, and access to the same allowed only to responsible parties. C. Must be thoroughly insulated from the ground, or permanently or effectively grounded, and the en- closure in which they are placed must be practically air-tight, except that it must be thoroughly venti- lated to the outdoor air, if possible through a chim- ney or flue. There should be at least six inches air space on all sides of the transformer. 37. Series Lamps. a. No multiple series or series multiple system of lighting will be approved. b. Must not, under any circumstances, be attached to gas fixtures. EXTRA-HIGH-POTENTIAL SYSTEMS. Over 3,500 Volts. Any circuit attached to any machine or combina- tion of machines which develops a difference of potential, between any two wires, of over 3, .500 volts, shall be considered as an extra-high-potential circuit, ELECTRIC WIRING. 261 and as coming under that class, unless an approved transforming device is used, which cuts the differ- ence of potential down to 3,500 volts or less. 38. Primary Wires. a. Must not be brought into or over buildings except power stations and sub-stations. 39. Secondary Wires. a. Must be installed under rules for high-poten- Tial systems when their immediate primary wires carry a current at a potential of over 3,500 volts, unless the primary wires are installed in accord- ance with the requirements as given in No. 12 A or are entirely underground, within city, town and village limits. 262 ELECTRIC WlRixNG. Fig. 93. A Switchboard, ELECTRIC WIRING. 263 8ths. A = .28125 H = .296875 J = .125 H = .34375 «i = .328125 i = .250 H = .40625 H = .359376 1 = .375 it = .46875 H = .390625 i = .500 H = .53125 H = .421875 f = .625 H = .69375 H = .453125 i = .750 li = .65625 *i = .484375 1= .875 fi = .71875 ii = .615625 leth*. 11 = .78125 H = .546875 A = .0625 |} = .84375 H = .578125 A = .1875 iJ = .90625 H = .609375 A = .3125 H = .96875 a = .640825 rV = .4375 64ths. « = .671876 ti- .703125 T'r = .5625 «v = .015625 H = .6875 ^T = .046875 « = .734375 H = .8125 f^ = .078125 tt = ti = .765625 .796875 5* = .9375 A = . 109375 Ji = .828125 33d«. 1 ic'r = . 140625 ♦ Ji = .859375 5'.= 03125 H = .171875 tJ = .890625 A = 09375 il- .203125 H = .921875 A = 15625 H = .234375 .953125 iV = 21875 iJ = .265625 J} = .984375 Table No. 11. Table of Decimal Eauivalenta. 264 ELECTRIC WIRING, l-OW aj aj tn tfi • ^ ^^ a.p.S.» CJ u u u c caa CO II li II II l-r U 1^ a> V oj V C d eS oS S. a Lg.ll H O •^ s^^ri^ 0) 5 0) Sa g'3 i 2 3^ flj a* a) flj Qj g.22Si-2SBi:5~.2-3.H.S W II II If II II II li II "il n W II II II 11 w fea-sa ft, SOoS . o § i 2 s - o 3 < ^ g K & fl to c b o O <» u . « "□ 1= d to >> ■< .41 M !(^S s £3.^ II I) It II II II II s^2|s.§5a 0) « a o B OS'S 33"3a«3a f-l "OiH '0»H s II II li II II 17 n >• 32"' 'S M d IT II II II II II ir ^^Sls sis ■B-a do* II IT a a BB il g'g' li IS M .'2 « S"^ . -SB" zi is3!233ao3 •- M a o II 1! li II 11 H II 3S»|g.SB| S a> p = = v^^ saog-g^ll o.2.g-o^ .Sg e II II II II II ¥ II ■a II II II II II II II ^lll III ■5 aS M t^SS-^ 03 -SC=3 S ELECTRIC WIRING. 265 ■9Jm JO OH 22R?;?385^5?3^K?5glgF;g5S35aS?;S?R? -jan MJW fiSBJH rfl^rfSiQt- , ooooooooooooooooooooo -qeniig m»m 00 «3«ao-i'CJ _ ,-_, . _ ooooooooooooooooooooooo f u 'uojaaJX 'oo aoji uoiuaix CJOOOOOOOOOOOOOOOOOC OOOOOO^OOOOOOOOOOOOOOO •sqnjs JO uj'Bi{Su{iuj!g O) CM tra CS oO tn C4 OOtDvrOCM AO SooSooooooooooSs •adjBqg ip uMOjg JO UBOiJSmv oooooooooo ooo oSSooooooc be ©JIM JO OM •ajjAV JO ON 5So<-'Nrt^»oi |goi-ic^wrin(*t-poo»o^WM^«2ocominomaOaoM NMC^NNC^M^ ES^^ESS; o>e>o>o>nao)a>t«r>t«i» OQOOOOOOgOQQOOpQOQU!u3w^r*tO SOSoQOQOOOOgoaSSQONclMIOWra oooooooooSooooSSMMtenis ^^iq oo'o'cTo'o'oo'o'o'oog'cs'o'o'.-^og " ' " -"- ||S= o o >« a 1:3 » C3 O ELECTRIC WIRING. 267 0) s OS < Ob 2§ W . N O ■< X-* (M CO 5 W.D CO O . ._ j< lOeD -^ 00 i-«WCOCDC5iO'9'00 — r- OOOS-^T^ t^ ^ ^ i-H i-H ■»*< Oi h- M cor^OooCsu^»oirt)C^^^CJ"-CTS(Mt»-l>-OacO .Oi :o -^ CO OS oi lO o CO C3 «c "^ '• io '"X> o 03 — ■«'QOS'ioococooocoMeo;DiracoTf ^H 1— I r-l C^ C^ 00 "N UTi W CD 00 CD OO N — ' ira CM r^ 00 ic r- ira c^ CO t^ 00 oo 00 N COOiCDOOCOOaCO :cr-oo-**t--tooocD «)»OCOod'*300iXiOSWOJ--D'*"*CD'* CJOSTOi— iO«D^^Oioo— 'C>ir~ca:D^(M ocsirt'Ooooi— "O'cr^r-coioi^irao i-ic^'^coc;oioO'*'Mcoir*030J rH .-I IM ■<*' CD Wa-^-^r 00 -ri CD-S'rfCDCDOOQO — 30coio:Dco^?r~i— ■a^t^^-cDo;'^l^- cOlr^— t^o— CMi~o*3"a30o— -^Qoo tDrt'Tj'iCCOCOl— COiOOOCOOr^I^OCO O^CD— ■COCOCOI"-r*OOCOl— ^i(T t^ i-'a i:0l-*asC^i005-rO00aD^r».i-c0»Oi CO (O CD CO-** eOlM'fC^— CDOOMOOOinTf*-- — 00— ' tOCDO:'M:DOS — OliOOSiiOOOWCDirtOOi eoiraooTi'(Nior*0'*a3ira'9''^oicDcooo i-HOJCOiOO'^CMCDi— "(MCDCO— "O I— lOacOCDOivCOI^OS .-I C-I CO tO 0000 f- .-I 00 CO 00 CO CO OSN^W .-( iO-roOOico^uor^'?^co— "uococ^r— O>o cor^oeoco05W i^t--OOiC'*CD005N0405WiOO^CO— <■— .— (i-«(MCO^iOi>-ooi-«'^r-cooouomr-c>) •-11— ^N'T^iro^usi'- M 00 T»* -M C>5 CD 00 CROliO-fOCt^^Tj* oa:D uOrfCDOOt— r-'MClOit^OOS-'J'Tf'M'* _3 cot~o;'^0'35«-«cococ^r-o0^-r^l^co'co Co Mcoiooimcoijoo:ococoos^Oir^t--oi <-H(Ncoco03ifi)'*'0^-r^iot»-co •—(N^COOiiDrt'Oi 1-1 tM CO OJOl O0TfC)'*(N'MOa CDQ0'»f'>3 r-cooaoiio — O'ncM'*— 'OQo — oococo I'-QOt^mt^iCCOcDCjaOCDi-Hi-iOOCOCOOD Eg — '^QOCO(3sr^I--OM/5Tf*ai»OCSOS(M' _ j=ci i-t— i-^wtMco-^or^Oi — k/:io>cooQOoo O-* 1— .-I i-H cs CO CO ■^ Eh 268 ELECTRIC WIRING. IT- ^a>i- oowiN CJ^»n t'-oo^ V r» eciftoo f-i»- CO J to -I c» r«*(0 ift 2 P9 o 00 « eo ;"g; JO « j2 2g^ bWa » ift i^ «o o -* 00 CO lO eo "-SSco ot*o^ wa>C4aoo»C4ooMoi <0^ »ai-*r-o»o*ciou5^«^c4SJ55eo3;3;»o*pi; r.^c.co-rtooo;-25?}RS??SSf:SSS|S a* eooowci ^Hr^CJeO'^^*0000»^'CO^c»«oseQ«>'-^oocor»wwj5veoM«-'jio6»Of-i ^ •^. ri^^tH .X .emoineeeeeoe f^M m^ tAC« r^r^^C4 GO ^lAiec* 06010^^ sssss 1^ Pi ELECTRIC WIEIXG. 269 Approximate cost per outlet, single lamp wiring, inside buildings (Based on a table prepared by C. L. Falconar) System Material Labor Total Iron gas pipe S3-25 S3-1S $6.40 Screwed solid .drawn tubing 3-4° 2.50 5-9° Armored cables 2.25 2 4-25 Ordinary screw socket joint conduit 2.05 2.05 4.10 Painted wood casing 1.84 1.46 330 Ordinary steel tubing with plain sockets 1-74 1.46 3.20 Ordinary wood casing 1.64 1.46 3.10 Insulators 1.58 1.29 2.85 Lead-covered wires (clipped direct) 1.40 1. 10 2.50 Insulators (cleat type) '■34 .96 2.30 Table 18. Cost of House Wiring. 270 ELECTRIC WIRING. *" 5 5.-S u u P. u a u 8 I too . - to IS CO o> lO'cf O O O Oe Q O OCOOCOOO 00 04 1. , aocooDoaooo'«-«o3ci«otcoaocoo ooo Nt.t-iHQoooO'*o»u3Cr-«0'*»eo ef » t^ «j -^ CO CO ci" iH* I-? iH J3n ooo o coco coco to ooo CO '-','*„'1P.<^,»0 0,*0 C^ O^QO (O US ^ 00 ^ o» co"'m'"o' (xT to"!©"^' «' c»* ci'iH-iH* i-T ooo O lOO 0> t-00 300 OO sioinioo ,— .. H "* -V C^ t- t-^rH C0_Q9^O ■^OS W C^Oi t- <0 'tfi COCO h' 0>" lo" C>f CT t«^ 5D ■* CO M ci" r-i" i-T i-T oooc o to o u COOPl 1- OOC OiOC » 1-m gooooinoiooootDUseieocJO iftoot-ogo>coQO'«sO'*t-eoceo ODinoo-tfcicowi-tcooooaocom-^co •^HCOMit-iHt-eoOOOtOlO^COCJC^r^i-tr-f to ^ CO C4 C4 i-H W 1-^ iflOOC C4 O O U iM >n in u 'do' OOC oiAknooiAOiAooinoowomt- OC t-'(0*Vco"coc« i-Tr-Tr-r oooc Sooc OOi- SOOOOOOOOOOOOOClOi-cJS soinmoor-ioiftooi-toof-ioinin 3«DC»CS^OQOtOlATj«COCJCl ocitnocoNOcocoia'^cocuMF 4n o o c» CJ cfl « OOOQOOOOOOOOiOO«0 OOOOC»OOOOC«OOCJOOf-l inin-44c«C4Cir-icDcooaoaoo'vo)ta 3 O O O O OO dO O O O O o 7 tn o in lo kn m ijc-^od'^'*^cii- D0DO-*0»inCJC K eoco ci p ■ ' ooooooooooocoomo ooooinoooooooinooM oooin-^inocicif-notooooooo u o oooQ«- lO : :0000« CJCO T? ID to C- ODOl o f-ioeo ■* into ; 't : : ; ■ oooo»H cNco •* »D-(c»eo : ci OOo'OtHCJeO-^lOtDC-OOftOi-IM - :::::|:eoo t-tw->r^ : r •:■■;; O " ' Eh ^ ELECTRIC WIRING. 271 CS o it IS: 3 O -^1 « O i^ 4) C So* Ci ■ODCOOi I CO ^i to s^-Hcoeoo_o |»l»^^^&t'^^^— COQOOOC • toSoiTKC 3 M cc ;o t-t r 1 CO r- co'co «] SSUSSS? ♦■r-oc ^ VMS I CO r^'^H t— a > I CO e* II It 3 MM I-''-* I— asoososg C4m^^ OCOCOW^eCM(NfH-^r-l 5 FH -^ ASoo «) « ■* c5 K c^iS — S ■HiC3in aooocooooa nnet Oi a zo n i-jr.MoaofOin'^MNNi-i'- iSiS 3QO (OrHOD 3«OQ0CC»ft OOOO o OStNMOS =0000000^00 c t3S OOOQOOOOOOOOC Sf-OM«r~— <^ODOU3 *c 3NI-*'<*"'-*C0f*'ft>*C0MW-«- oo oc r- 1:000 c 5° i2« ea p tOOQO lOOQor^ lOO^COOJ 00SC«Or».iooso>--to4CT3TiI''a i-^ M -^ CO OO O 0« ssssassssa t SggSSSfegSS a a s sg;s3gssssfessg 1 OC0C0-*«O00i:D-.j t iocen>ooos';:jr-iCfleo^i05pt- '¥>"*iNOQOcO-*CaOCOeD'*Cl a U3iC10lOiOlOiOU3COCDCOCOCO MOOOCD-^NOCCC-^NOOO 1 g§5!?!^5!§«5:^?gS 1 50^'^WdcoeO'^NOooco^ 1 sfesasssssss^feg u cS ■*