W-4S ■A ,8ERTR. ' LIBRARY AT -r"V' ■^ I '-I ifllllllil iTi'iin ^'" '-'°''*"» 3 1924 073 975 611 The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924073975611 Production Note Cornell University Library produced this volume to replace the irreparably deteriorated original. It was scanned at 600 dots per inch resolution and compressed prior to storage using CCITT/ITU Group 4 compression. The digital data were used to create Cornell's replacement volume on paper tiiat meets die ANSI Standard Z39.48- 1992. The production of this volume was supported by the United States Department of Education, Higher Education Act, Tide II-C. Scanned as part of the A. R. Mann Library project to preserve and enhance access to the Core Historical Literature of the Agricultural Sciences. Titles included in this collection are listed in the volumes published by the Cornell University Press in the series The Literature of the Agricultural Sciences, 1991-1996, Wallace C. Olsen, series editor. PRACTICAL ELECTRICITY for BEGINNERS GEORGE A. WILLOUGHBY SHOP SUPERVISOR ARTHUR HILL TRADE SCHOOL SAGINAW, MICHIGAN THE MANUAL ARTS PRESS PEORIA, ILLINOIS COPYRIGHT, 1921 GEORGE A. WILLOUGHBY 52 D83 Prmttd tn the Vnitei Slatts . How are dry cells connected to increase the pressure ? 10. What care should be taken in using a storage battery? 11. What is a hydrometer? ELECTRICAL PRESSURES 27 12. How is it possible to avoid running down a storage battery? 13. What advantage has the eenerator over the storage battery? 14. How do you take hydrometer readings? Suggestions 1. Dry cells are frequently thrown away and may be obtained with- out cost. See if you can get an old one and "liven it up" by chipping the wax from the top and pouring water in it. 2. Tear an old dry cell to pieces and see if you can learn more about its parts than is given in this book. 3. If you have an automobile, try to locate the storage battery and see how many cells are connected in series. Each cell gives two volts. What is the voltage of the battery? 4. Look at the meter on the dash the next time you take an auto ride and see if it reads "charge." 6. Watch the meter when the lamps are on and see if it reads "dis- charge." €. The meter does not read when the starting motor is used because so much current is taken that it would be burned out. See that this is true by watching the meter when the motor is being started. 7. If you have a doorbell in your bouse see if you can locate the dry cells that furnish the pressure for it. 8. If you have a doorbell and cannot locate any dry cells it is possi- ble that the bell is operated from a small bell-ringing transformer con- nected to the lighting circuit. If this is thought to be the case, see if you can locate the transformer. CHAPTER IV The Flow of Electrical Cuekent ; Electrical Circuits 20. Flow of Electricity vs. Flow of Water.— Having become familiar with the fact that electricity is caused to move thru materials that are conductors if electrical pressure Fig. 10. Showing an important difference between the flow of water and the flow of electricity. Electricity will not flow unless there is a complete circuit. or voltage is supplied, let us now consider the facts surround- ing the flow of electrical currents. The flowing of electricity is like the flowing of water in some respects, but decidedly different from it in others. "Water will flow out of the end of a pipe or hose if pressure is applied. Electricity will not flow out the end of a wire or other conductor. Before it is possible to make electricity 28 FLOW OF ELECTRICAL CURRENTS; CIRCUITS 29 flow, it is necessary to provide a complete circuit for it; that is, there must be a continuous conductor, or series of con- ductors, leading from one terminal of a battery aroimd thru the point to which the current is transmitted and back to the other terminal. Just the opposite is true in the case of a •*" y^^=r 1 \ 1 r .0^^?^^ lU f Fig. 11. Illustrating the fact that water flows slowly thru a small pipe, but rapidly thru a large one, just as electricity flows slowly thru a small wire, but rapidly thru a large one. water circuit formed by making two connections to a tank. No water will flow if a closed circuit is formed by running a pipe from the tank to the point where the water is desired and back to the same tank again. These points are illustrated in Fig. 10. 21. What Affects the Flow of Electricity. — There are three very important points brought out so far which should be kept in mind constantly. First, conductors are required 30 PRACTICAL ELECTRICITY FOR BEGINNERS for carrying electrical currents. Second, electrical pressure or voltage must be supplied by a battery or generator before electrical currents will flow thru the conductors. Third, the conductor, or series of conductors, must form a closed circuit from one terminal of the source of current to the other, or no current will flow. It is not sufficient, however, to say that conductors, pres- sures and closed circuits are all that are required without Copper Wire S-1 Iron Wire Fig. 12. Showing the flow of current thru a copper wire and an iron wire of the same diameter and length when connected to dry cells of the same kind. About seven times as much current flows thru the copper as thru the iron, due to different electrical properties of the two metals. going more into detail as to the other things affecting the flow of electricity. Water flows slowly out of a small pipe, but rapidly out of a large one. Likewise, electricity flows slowly thru a small wire and rapidly thru a large one (Fig. 11). Then, if a short, heavy wire were connected to the terminals of a dry cell, a very large current would flow. If this were re- placed by another copper wire of the same length, but smaller in diameter, less current would flow. If this were continued, replacing the wire each time by one smaller in diameter, the flow of current would be less after each change. The same FLOW OF ELECTRICAL CURRENTS; CIRCUITS 31 would be true if different sizes of pipes were connected to a tank of water; but if iron wires of the same size were substi- tuted for those of copper, only about one-seventh as much current would flow in each case (Fig. 12). The material of which the conductor is made has a great deal to do with the speed at which it will carry electricity. No two materials will carry it with exactly the same ease. Now, if wires twice as long were used, it would be foimd that in every case only Fig. 13. Indicating the difference in the flow of current thru a short wire and a long wire of the same material and size. If the wire is twice as long, only one-half as much current will flow thru it. one-half as much current would flow thru them, as illustrated in Fig. 13. The foregoing may be summed up in the following: The ability of a conductor to carry electrical current de- pends upon (1) the diameter of the conductor or its cross-sec- tional area, (2) the material of which the conductor is made, and (3) the length of the conductor. 22. Resistance. — These facts — that the ease with which the current flows thru a conductor depends upon the size of the conductor, the material of which it is made, and its length — are of great importance and should be remembered by the student. If these were not true, we would have no 32 PRACTICAL ELECTRICITY FOR BEGINNERS electric lights, electric toasters or electric heaters, because these all depend upon "resistance" for their operation. Resistance is the physical property of a material by virtue of which the material opposes the flow of electrical current. The resistance that the different materials offer to the flow of electricity varies greatly. No material is a perfect conductor, and no material is a perfect insulator. However, some mate- rials have such a small amount of resistance that they are called conductors, and others have so much that they are called insulators. 23. Simple Electrical Circuits. — Having learned the important points regarding electricity, its transmission and its flow, the reader is now in a position to understand some of the more simple electrical circuits and, perhaps, to do some simple wiring. No attempt will be made at this time to ex- plain why or how the different pieces of electrical apparatus operate — why a bell rings or why a lamp lights — ^but it will be taken for granted that if proper cormections are made be- tween the battery and the device to be operated, such as a bell or battery lamp, the bell will ring or the lamp will light. Since we know that a complete conducting circuit must be formed before current can flow, it is evident that two wires must be connected to every piece of electrical apparatus. Every circuit must lead from one side of a battery to one side of the bell, or lamp, and from the other terminal back to the other battery terminal. 24. The Bell Circuit. — The simplest method of con- necting a bell to a dry cell is to touch its terminals to those of the cell. The current then flows directly thru the bell and causes it to ring. Such an arrangement as this would be of FLOW OF ELECTRICAL CURRENTS; CIRCUITS 33 very little value, however, and is never iised. In hoijses or other places where bells are used as signals, the battery and the bells are some distance apart. This being the case, let us consider connecting a bell to a dry cell under practical condi- tions. It is evident that two wires of the proper kind must be nm from the bell to the dry cell. If this be done, however', as the last connection to the cell is made, the bell will start to ring and will continue to do so until the wire is disconnected again, or until the battery is used up. To make possible the controlling of the bell in such a case, it is necessary to leave one of the wires disconnected from the dry cell and to touch it to the cell terminal when it is desired to have the bell ring and remove when it is to be stopped. This is, of course, very inconvenient and unpractical, and it is not desirable to have to control the bell from the battery. Suppose, now, that we try to provide a method whereby the bell can be controlled from a point half-way between it and the battery. The wire that has been left disconnected from the cell can be cut in two and the end nearer the cell connected to the terminal without causing the bell to ring, be- cause the circuit is open at the point where the wire is cut. All that is necessary to make the bell ring after this has been done is to close the circuit by touching the bared ends of the wires at the point where the cut was made. Such an arrange- ment is shown in Fig. 14. This provides a method of control, but it is not very satisfactory because the wire ends are rather inconvenient to handle and it is non-practical in many ways. To make possible the controlling in a similar manner, but by a much more convenient method, the push-button has been devised which makes an opening in the circuit as does MILS-i T-- a 34 PRACTICAL ELECTRICITY FOR BEGINNERS the cut in the wire, but which provides a simple and con- venient means of closing it. 25. Push-Buttons. — Push-buttons are made in a va- riety of forms with wood, hard rubber, or porcelain bases. Upon the base plate are two contact parts of springy metal (Fig. 15, B and C). They are ar- ranged in such a way that when no pressure is applied to B, they re- main separated, thereby causing a break in the circuit, which is the equivalent of having the bell dis- connected from the dry cell. When the button A is pushed, the parts B and C come together and the circuit is closed, which is the equivalent of Fig. 14. The connec- * +i, -i n tt i tions required for operat- connectmg to the dry cell. Holes 'p7ov1sion"is made f o^oren: ^'^ P^^^ed in the base for fasten- ing and closing the circuit j^g screws and for wires to be con- at point A. ° nected to the contact parts. DRY CELL 26. Connecting Bell Circuits. — It will be seen, by re- ferring to Fig. 16, that when a push-button is installed in a bell circuit, three pieces of wire are required for the complete circuit — one from the bell to the push-button, one from the button to the dry cell, and one from the bell to the dry cell. In attaching the wires to the bell terminals, the cell terminals and the push-button strips, care must be taken to scrape the wires bright and clean, and when connecting to the screws, the wires should be bent into the form of a loop and placed under the screw heads to insure good contact. FLOW OF ELECTRICAL CURRENTS; CIRCUITS 35 27. Important Points Regarding Connections. — It must be borne in mind at all times that whenever connections are made, good contact must be made between the two con- ductors thus joined, because the electricity is forced to go from one conductor to another. If a connection is attempted without making good contact, the current will not flow because of the high resistance oh'ered by the poor joint. To avoid this trouble, always see that terminals and con- necting wires are clean and bright, and that good contact is formed between the conductors. 28. Troubles in Bell Circuits.— The most common causes of trouble in bell cir- cuits are weak or worn-out batteries, dirty terminals or loose coriuections on the push- button, loose connections on the bell, break in the circuit known as open circuit, or short-circuited wires. A short circuit means a connection between the wires before they get to the bell which permits the current to flow from one terminal of the battery to the other without getting to the bell. 29. Repairing Bell Circuits. — Weak or worn-out bat- teries must be replaced. It is well to have a good bell and a good battery on hand when testing for troubles. Try the good bell on the batteries, connecting it directly to the termi- nals. If the battery is good, look for one of the other troubles. The push-button should be taken apart and cleaned thoroly. If the bell does not operate after the battery and the push- button have been inspected, it is well to try a new bell in the place of the other. If this bell does not ring, there must be a Fig. 15. Cross- sectional view of the top of a push- buttonandthebase upon which it screws. 36 PRACTICAL ELECTRICITY FOR BEGINNERS break in the circuit, or a "short." To test for a short (Fig. 17), disconnect one of the wires from the battery, and connect it to one terminal of a good bell, then connect the other side of the bell to the battery. If it rings, there is a short circuit. Another way to do this without the 'use of a bell is to touch the wire dis- connected from the battery, and the short one connected to it for testing, to the tongue, keeping them about one- fourth of an inch apart. If current flows, a sort of sour taste will be no- ticed. These tests should be tried with the push-button closed. If a Fig. 16. Diagram of a ^^°^ ^ detected, it may be found to simple complete bell cir- be due to cutting of the insulation by cuit. staples, especially if some poor elec- trician has put two wires under one staple. Fig. 17. Diagram showing how to test for a short circuit. The ringing of the test bell indicates a short. The test bell may be omitted and the wires connected to it placed on the tongue. To test for a break, close the push-button or short-circuit it; disconnect one of the wires from the battery, and connect FLOW OF ELECTRICAL CURRENTS; CIRCUITS 37 a bell between it and the terminal from which it has been removed (Fig. 18). Then take a test wire and at intervals along the wii'es running to the bell, remove a little insulation on both wires and connect the test wire across it. If the gns— ■ Q Test Bell Br»oU S Test wire ■^ Fig. 18. Diagram showing how to test for a break in a bell circuit. The ringing of the test bell when the test wire is in the first position and its failure to ring when the wire is in the second position, indicate the break. test bell rings, the opening is nearer the main bell. This should be continued imtU the vicinity of the break is located, and then finally the break itself. Summary of Principles in Chapter IV 1. Electricity will flow only thru a complete conducting circuit. 2. The material of which a conductor is made and its size greatly affect the flow of current thru it. 3. Resistance is the physical property of a material by virtue of which it opposes the flow of current. 4. The resistance of a conductor depends upon its size, its length and the material of which it is made. 5. When connections are made, great care must be taken to have the conductors clean and bright and to bring them into close contact. 38 practical electricity for beginners Questions 1 . How does the flow of electricity differ from the fiow of water ? 2. Will electricity flow out the end of a conductor? 3. What 13 necessary before an electrical current can be made to flow? 4. What affects the flow of electrical current thru a conductor? 6. What is meant by resistance? 6. Upon what does the resistance of a conductor depend? 7. Which has more resistance — iron or copper? 8. What are push-buttons and how do they operate? 9. How are push-buttons connected in a bell circuit ? 10. What care must be taken in connecting a bell circuit? 11. Where is the bell usually placed in a house? 12. Where is the piish-button usually found in a house installation? 13. Where is the dry cell usually placed in a house? 14. What are the most common causes of trouble in bell circuits? 16. How are these troubles remedied? Suggestions 1. If you can procure the required materials, try the connecting of the bell to a dry cell as described in this book. 2. Try to connect two bells in such a manner that they are both operated and controlled by one battery and one push-button. 3. Connect two bells with an individual push-button for each, using only one battery, as is often the case in a two-family flat or an apart- ment house. 4. Connect one bell controlled by either of two push-buttons, as is the case when push-buttons are placed at two locations. 5. Purposely place some of the troubles mentioned in this book in a bell circuit and try the tests until you become familiar with them. CHAPTER V Battery-Lighting Circuits 30. Importance of Battery Lighting.— Battery light- ing is at the present time of very great importance and will undoubtedly continue to become of even greater significance because of its extensive use in automobile work. Every mod- ern automobile is provided with electric headlights, an elec- tric dash light, an electric tail light, and many are equipped with spot lights, dome lights, etc. It is obvious that this type of lighting will always be required, and that it will be impos- sible to supply the necessary electrical pressure in ways other than by the use of a battery or low-voltage generator because of the necessity that the complete system be portable and complete within itself. 31. Why Battery Lighting Should Be Studied. — It is evident that it is well for everybody to learn something about battery lighting if for no other purpose than to make himself familiar with the lighting of his automobile. This alone is sufficient reason for making a careful study of this subject, but in addition to the value of a knowledge of this work as ap- plied to automobiles, it is invaluable in teaching the various methods of connecting lamps, the different arrangements of switches, and wiring installations of various kinds. The sub- ject is one of very great importance, and can only be touched upon in this book. We shall take it for granted at this time that if proper connections are made to the lamp receptacle or socket, the lamp will light up properly, and will consider, 39 40 PRACTICAL ELECTRICITY FOR BEGINNERS mainly, connecting rather than the detecting of troubles. The latter will be taken up in a later work. 32. Brief Description of Battery Lamps. — ^A battery lamp is one designed for use with dry cells, storage batteries, or other low- voltage sources, and is so constructed as to i)er- mit enough current to flow thru it to cause it to light. The t5-v-Lomp amount of current flowing thru the lamp when it is con- nected depends upon the pres- sure, and the resistance in the lamp itself. The lamps are made for use in connection with small receptacles orsock- ets and are put into place, after the wiring for them has been completed, by turning them into the receptacles or pushing them in as the case may be. Fig. 19. A 1.5-volt lamp con- nected to a 1.5-volt source of pressure, a dry cell. 33. The Meaning of the Mark on a Battery Lamp. A battery lamp is usually stamped with a number giving the voltage upon which it is designed to operate. A mark of 1.5 V on the base of the lamp means that it is fnade for use on an electrical pressure of 1.5 volts, and a mark of 6 V means that it is intended for use on a 6-volt battery. One should be very careful when using battery lamps to see that the pressure applied is not too great, for too great a pressure will spoil them (Fig. 19). 34. Effect of Operating a Lamp on Too High Voltage. The connecting of a low-voltage lamp on a high-voltage bat- BATTERY-LIGHTING CIRCUITS 41 tery or line is as disastrous as connecting a toy balloon onto an air-line provided for inflating automobile tires. Care should be taken in every case to note the voltage mark on the lamp and to make sure that the pressure supplied by the 5- V- Lamp 3 Volts Fig. 20. A 3-volt lamp connected to a 3-volt source, two dry cells connected in series. battery upon which it is to be operated does not exceed this value. 36. Effect of Operating a Lamp on Too Low Voltage. Let us consider what would happen if the voltage of a battery upon which a lamp is to be operated is not suflBciently high; that is, say a 6-volt lamp is connected to a battery giving only 3 volts pressure. If the pressure is insufficient, the effect would be the same as an insufficient pressure on a stream of water that is supposed to have a ^ven velocity. We know the water would not run as fast as it is intended that it should. Likewise, the current would not run thru the lamp with the required speed, and the lamp would bum dimly or not at all. K a lamp does not light up properly 42 PRACTICAL ELECTRICITY FOR BEGINNERS b-V Lai g Volts 4^^ of when good connections are made, it is an indication that the voltage is not high enough. 36. What Determines the Voltage of a Battery. — ^A battery is usually considered as several cells connected to- gether, and the total voltage depends upon the number of cells. A single dry cell gives a voltage of about 1.5, and a storage cell gives about 2 volts. The total voltage of a battery is equal to the voltage of one cell multiplied by the number of cells. The voltage of two dry cells connected in series is equal to 5 X 2 or 3 volts, and the voltage a three-cell storage battery is 2 X 3 or 6. If a 3-volt lamp is to Fig. 21. A 6-volt lamp con- be operated on dry cells, it is evi- vKto\°a|e\\" te^Kree' dent that two cells would be con- cells connected in series. jiggted in series (Figs. 20 and 21) . 37. How Battery-Lighting Circuits Differ from Bell Circuits. — In battery-lighting circuits battery switches are used instead of push-buttons for controlling the lamps. Then, too, in automobile lighting we often have what is called a one-wire system of wiring. This statement might be mis- leading to the beginner, but is easily explained. The current does not flow to and from the lamps thru the same wire, but is led to them thru one wire, and the other sides are con- nected to the frame of the machine which is metal and a con- ductor, and in that manner one wire is done away with (Fig. 22). BATTERY-LIGHTING CIRCUITS 43 38. Parallel and Series Connecting of Lamps. — Be- cause of the use of two different methods of connecting lamps on an automobile, it is advisable to give a brief description of these two methods at this time. These two methods are called parallel and series. By connecting two lamps in parallel (Fig. 23), we mean the con- necting of the lamps by two wires and then making the bat- tery connections to both terminals of either lamp or Fig. 22. A very simple one-wire system. The frame of the automobile takes the place of the other wire. 6-V Battery Rarollel Fig. 23. Two lamps (6-volt) connected in parallel to a 6-volt storage battery. Each lamp operates independently of the other. to the two wires. It will be seen that if one of the lamps is completely removed when they are connected in this manner, the other is unaffected. By series connecting two lamps (Fig. 24), we mean the connecting of one terminal of one to one terminal of the other and then connecting the battery wires to the two remaining terminals. With this arrangement 44 PRACTICAL ELECTRICITY FOR BEGINNERS neither lamp will operate if anything happens to either, be- cause current cannot flow thru one without flowing thru the other. This combination is used in connecting the dash light and the tail light on an automobile so if the tail lamp is broken or burned out, the dash light will go out also and in- dicate the trouble. All of the other lamps on an automobile are usually connected in parallel. It must be remembered b-V BoHerjt Series Fig. 24. Two lamps (3-volt) connected in series to a 6-voIt bat- tery. The failure of either lamp to operate will cause the other to cease to light. that if two lamps are connected in series, their voltage must be only one-half that of the battery upon which they operate; that is, if an auto is equipped with a 6-volt storage battery and all of the lamps are connected in parallel except the dash and tail lights, all lamps will be 6-volt except these two, and they will be 3-volt. 39. How Lamps Are Dimmed. — ^Another important re- quirement in automobile lighting is the making possible of the operating of the lamps either "bright" or "dim." This is accomplished by cutting down the amount of current flowing thru the lamps when it is desired to make them dim, and giv- ing them the full required amount when it is desired to have BATTERY-LIGHTING CIRCUITS 45 them bright. Two different circuits are usually provided be- tween the switch and the battery, and a resistance is inserted in the one, as shown in Fig. 25. When the switch is turned so the current must be forced thru the circuit containing the resistance, a smaller amount gets to the lamt)s, which is the Fig. 25. Showing one common method of making possible the light- ing of lamps brightly or dimly. The resistance causes a dimming of the light. equivalent of reducing the voltage impressed upon them, and they give a dim light instead of a bright one. Summary op Principles in Chapter V 1. Battery lighting is a very important subject because it is ap- plied so extensively in automobile work. 2. Battery lamps are made for use on low voltage. 3. Battery lamps are stamped with the voltage upon which they are supposed to be operated. 4. Connecting a lamp to too high a voltage ruins it. 6. Connecting a lamp to too low a voltage line catises it to burn dimly or not at all. 6. The voltage of a battery is equal to the voltage of a single cell multiplied by the number of cells. 7. The voltage of a dry cell is about 1.5. 46 PRACTICAL ELECTRICITY FOR BEGINNERS 8. The voltage of a storage cell is about 2. 9. Lamps connected in parallel must be for the same voltage as that of the battery upon which they are to operate. 10. The voltage of lamps connected in series must be equal to the voltage of the battery divided by the number of lamps to be operated. 11. Connecting a resistance in a lamp circuit causes the lamp to burn dimly. Questions 1. Where is battery lighting used most extensively? 2. Why is it important to have a knowledge of battery lighting? 3. How does a battery lamp differ from any other electric lamp? 4. How is it possible to tell upon what voltage a lamp is supposed to be operated? 5. What happens if an attempt is made to operate a lamp on too high a voltage? 6. What effect does operating a lamp on too low a voltage have? 7. How is the voltage of a battery determined? 8. What is the voltage of a dry cell? 9. What is the voltage of a storage cell? 10. How do battery lighting circuits differ from bell circuits? 11. How is it possible to have a "one-wire" lighting system? 12. How do you connect lamps in parallel? 13. How do you connect lamps in series? 14. Where is the series arrangement of lamps most commonly used? 15. How is it possible to make lamps either bright or dim as de- sired? Suggestions 1. Battery lamps of various voltages are available at a price of only a few cents each, as are also the receptacles and switches used with them. They are exceedingly valuable in teaching many connecting circuits and for experimenting purposes. If you can procure some of them, try some of the following: 2. Operate a 3-volt lamp on dry cells. 3. Operate two 1.5-vclt lamps on one dry cell. 4. Connect a 1.5-volt lamp and a 3-volt lamp in such a way that they can be operated from a two-cell battery. 5. Try any of the wiring systems you have in your automobile or in your house. CHAPTER VI The Heating Effect op Electrical Current; Practical Applications 40. The Effects of Electrical Currents. — We are fa- miliar with many of the resiilts of the action of electricity in motion, and have made use of it for some purposes, such as ringing bells and lighting small lamps, without taking into consideration what the current actually did to bring about these results. We will simply mention at this time the va- rious effects of electrical currents and take up in detail the more simple of its applications, leaving the others for later volumes. The effects of electrical currents are of immense commer- cial importance, their applications in useful ways making pos- sible the ringing of bells and the operating of other signaling devices; the heating of flatirons, toasters and other heating devices; the lighting of electric lamps, and the operating of electric fans, washing machines, street cars and other elec- trical machines and devices. These accomplishments are due to a few effects which may be simimed up as follows: The heating effect of electrical currents, The magnetizing of iron and steel when electrical currents are conducted around them. The creating of magnetic fields, and The causing of induced currents. Only the first of these will be taken up in this book. 41. The Heating Effect of Electrical Currents. — Wc are all familiar with the fact that electric-light bulbs get hot, '•'7 48 PRACTICAL ELECTRICITY FOR BEGINNERS and the reader may have seen electric flatirons, electric stoves, electric toasters, electric heating pads, electric grills, electric percolators, and the like, without realizing that every electrical current, however small, causes some heat. The fact is that whenever electrical current flows thru a con- ductor, heat is generated. The amoimt of heat may be small, however, and in many cases it is unnoticeable. To generate heat is one of the properties of an electric current which makes it of great value. -r,. o^ u ^ ^^ Fig. 26 shows diagrammatic- ally the heating effect of elec- trical current, altho a storage battery is sel- dom used in this way. zr\ ^S^ STOimu. eMTTcnv -vwwwv Resifctonce Wi"r«/ Fig. 26. Illustrating the heating effect of elec- trical current. 42. How the Working of Electricity Is Like the Work- ing of a Man. — Everybody is familiar with the fact that when one works hard or runs fast, he becomes warm, and that the harder he works or the faster he runs, the warmer he be- comes. In fact, it is possible when one is cold to get warm by moving around, running or exercising. Yet it is possible for a man to work and still keep cool if his task is not too difficult and he does not try to work too fast. The amoimt of heat generated when a man works depends upon the dif- ficulty encountered in bringing about the desired effects and changes and the speed at which he expends his energy. It seems that the flow of electrical current thru a conductor has somewhat the same effect upon the conductor as the moving HEATING EFFECT OF ELECTRICAL CURRENT 49 of his muscles has upon the man; that is, it causes the gene- ration of heat. 43. Things Affecting the Amount of Heat Gener- ated. — The amount of heat generated when an electrical cur- rent flows thru a conductor depends upon the difficulty en- countered by the current in passing thru the conductor and the rate at which it is forced to flow (Figs. 27 and 28) ; that is, the heat generated when electricity is forced thru a conductor Fig. 27. Showing the amount of heat generated when a certain wire of high resistance is con- nected to a dry cell. Fig. 28. Showing the amount of heat when the same wire as used in Fig. 27 is connected to two dry cells connected in series or twice as much pressure. A greater amount of heat is generated. depends upon the resistance of the conductor and the rate at which the current is forced to move. This being true, it is possible to force considerable current thru a large wire having a low resistance without causing the development of much heat, while, on the other hand, it is possible to select a con- ductor having a very high resistance and to cause the genera- tion of a large amount of heat by forcing only a comparatively small amount of electricity thru it. 44. How the Generation of Heat Can Be Regulated. — It has been shown in the previous discussion that the resist- ance of a conductor depends upon its diameter (or cross-sec- 50 PRACTICAL ELECTRICITY FOR BEGINNERS tional area if it is not round) ; its length, and the material of which it is made. It is necessary, then, only to select some metal having a very high resistance and a very high melting point, to put it into some convenient shape, and to select the proper length, to make the heating element of a device to be used for heating purposes. The se- lecting of the material, mounting it in the proper way, insulating the heat- ing element from the frame of the de- vice, and making proper provision for connecting to the source of cur- rent, are all problems which are more or less diflBcult. These are, however, problems arising in the design and manufacture of the devices, and we are more particularly interested in their principles rather than their manufacture. Fig. 29. Illustrating the heating eflEect of elec- trical current. The fine wire becomes very hot, and the large wire re- mains cool because of the difference in resistance. 45. The Principle Upon Which Heating Devices Operate. — Every common heating device depends upon the generation of heat by passing electrical current thru a conducting material, called a heating element, having a very high re- sistance, and all that is necessary for the satisfactory operation of the device is the passing of the required amount of elec- trical current thru it. To illustrate the heating effect of an electrical current, consider the arrange- ment shown in Fig. 29. Two heavy copper wires are con- nected to the terminals of a dry cell, or storage battery, and Fig. 30. Dia- grammatical sketch of a heating element. HEATING EFFECT OF ELECTRICAL CURRENT 51 between their ends is connected a piece of very fine wire, about the size of a thread. As soon as the circuit is com- pleted and current flows thru the conductors, the fine wire will become very hot and, perhaps, biim up while the others remain cool. This is due to the fact that the fine wire offers a very high resistance to the flow of the current, and when electricity is forced thru a conductor which offers a high resistance, the conductor becomes hot. The large wires offer but little resistance to the flow of the current and, conse- quently, remain cool. It is very important to understand that this is true, and it is well for the student to try it if the required materials are available. 46. Simple Heating Element. — Fig. 80 shows diagram- matically the heating element of an electric toaster. It is simply one continuous piece of high-resist- ance material in the form of a wire or ribbon so arranged that its ends can be connected to the source of current. All other heating elements are similar to this in principle, the only difference being in the shape. In every piece of heating apparatus, then, one may expect to find a piece of resistance material ar- ranged in some convenient maimer so the connections can be made to it and electrical current passed thru it. 47. The Electric Flatiron. — Fig. 31 shows an electric flatiron and its heating element. The resistance wire in the HiQH-resi»fawce wfw^ Fig. 31. Sketch of an electric flatiron, together with the heating element used in it. 62 PRACTICAL ELECTRICITY FOR BEGINNERS element is wound around a properly-shaped piece of suitable insulating material, and its ends are attached to heavy metal- lic pieces which project thru the top of the iron to provide for making connections to the source of current. Other heaters are provided for in a similar manner. Summary of Principles in Chapter VI 1. The flow of electrical currents cause several very important effects. 2. The heating effect of current flowing thru a conductor is one of very great importance. 3. Some heat is generated whenever electricity flows thru a con- ductor. 4. The amount of heat generated depends upon the resistance of the conductor and the amount of current flowing thru it. 5. All heating devices are practical applications of the heating effect of current flowing thru a conductor of high resistance. Questions 1. What are some of the results brought about by the use of elec- tricity? 2. With what effect of electricity are you most familiar? 3. Describe what is meant by the heating effect of electrical current? 4. Upon what does the amount of heat generated by an electrical current depend? 5. What must be borne in mind in selecting material for heating elements? 6. Why don't the terminals on a flatiron get red hot? Suggestions 1. If you have any heating devices available, examine them care- fully and see if you can trace the path of the electrical current thru them. 2. If you can procure any old heating device, take it apart and see if you can find out what is wrong with it. 3. If you have the opportunity, make some kind of a heating de- vice, however simple it may be, so as to fix the points brought out in this book firmly in mind. CHAPTER Vn Fuses and Their Purposes 48. Why Study Fuses. — Because of the extensive use of heating and lighting devices in the home, it is necessary that everybody be somewhat familiar with the important points relative to their operation and care. Many little difficulties may be encountered which may be overcome very easily, and at no great expense, by one familiar with their possible causes and the manner in which they may be overcome. Before the reader can be in a position to detect and remedy all of the possible troubles in the operation of heating devices, he must know what fuses are and what they are used for. They are used in every house installation and in nearly every other electrical circuit except bell and signaling circuits. 49. Brief Description of Purpose of Fuses. — Fuses are safety devices placed in an electric circuit for the purpose of protection. Suppose, for example, an accidental connec- tion is made between two metallic pieces forming the parts of an electric circuit, or that the insulation is accidentally re- moved from parts of the two wires of a circuit and they come in contact with each other. This would form an easy path for the electricity because it would not have to flow thru the high-resistance element of a heater, or other device, and, con- sequently, a very large current would pass thru the wires. This might be sufficient to bxim the insulation off the wires or, perhaps, to set the house on fire. Then, too, a large amount of power would be used up and no benefit derived. To do 64 PRACTICAL ELECTRICITY FOR BEGINNERS away with any possibilities of such an accident, fuses are con- nected in the circuit. 50. Brief Description of Fuses. — Fuses have in them a piece of metal which is known to be capable of carrying only a limited amount of current without melting. Thus, if a fuse marked "10 amp." is used in a circuit, only ten amperes can be drawn thru the circuit without melting the fuse-wire. If more than this is forced thru, the fuse will melt and open the circuit. Fuses are made in several different forms, the most common of which is the plug type (Fig. 32). This fuse is made so it can be screwed into a receptacle as a.lamp would be. By doing this, it is connected in the line in such a manner that all of the current flowing must flow thru it. If more current is drawn than the fuse is designed to stand, it simply "blows" and opens the circuit and no harm is done except the burning of the Fui* WiVe fuse wire. Another type of fuse used in some cases is the cartridge fuse (Fig. 33). Very small ones of this type are generally used in automobile lighting circuits, and, in some cases they are placed on the inside of the switch-box cover. 51. Testing a Fuse. — Sometimes it is desirable to be able to determine whether or not a fuse is good. Two fuses are usually placed in a circuit, and one may blow and the other remain unaffected. It is necessary in such a case to de- termine which of the fuses is the blown out one and to replace Fig. 32. plug fuse. Common Fig. 33 fuse. Cartridge FUSES AND THEIR PURPOSES 55 Fig. 34. Showing a simple method of testing a fuse. it with a good one. This can be done in any of several ways. A bell and a dry cell may be used, as in Fig. 34, in which case one wire is connected to the bell and the dry cell, and another to the bell only. This wire is then held in contact with the side of the fuse plug and the bottom of the plug is held in contact with the terminal of the dry cell, or connected as shown. If the bell rings, the fuse is good, but if it doesn't, the fuse has been blown. Another method is to con- nect two lamp receptacles in series, one after the other, and to place a lamp in one and the fuse in the other. If the lamp lights up, the fuse is good. See Fig. 35. The following is another method which can be used with little difficulty, but which must be done carefully. It is a method for use right at the fuse block. Close some circuit in the house — turn on a lamp or heater — open the main switch and remove the fuse that is thought to be blown. Screw a lamp into the fuse receptacle. Then, close the main switch, and if the lamp lights up at all, the remaining fuse is good. 62. Arrangement of Fuses in Houses. — In many of the more simple electrical installations in houses, the fuses are provided for in the base upon which the entrance switch is mounted, as shown in Fig. 36. In such an installation, this fused switch is placed at the point where the power wires 56 PRACTICAL ELECTRICITY FOR BEGINNERS enter the house, in such a way that all of the current used in the house must pass thru it. In such a case, none of the electrical circuits in the house will furnish power if this switch is open or if one of the fuses is burned out or removed. In larger installations, more than one set of fuses is used. Those at the entrance switch are of great enough capacity to carry all of the cur- rent used in the house, and the others are placed in individual circuits (Fig. 37). These indi- fuae P^G. 35. Showing another method of testing a plug fuse. vidual circuit fuses are of smaller capacity than the entrance switch ones. They are usually 10 amp. As an example, sup- pose that in one room of a house a piece of heating apparatxis is being used while most of the lamps in the house are being used at the same time. Now, if a short circuit should be formed in any of the circuits, all of the lamps and the heater would be turned off by the blow- ing of a fuse if the single set of fuses is used as described above. If, however, two sets of fuses are provided in addition to those at the entrance switch, one set in the lighting circuit and one set in the heating circuit, only one of these would be affected by the blowing of a fuse. If two sets of lighting circuit fuses were provided, only part of the lamps would go out when a fuse is accidentally blown. Fig. 36. A sim- ple entrance switch. FUSES AND THEIR PURPOSES 57 Branch Circuita 53. Replacing Fuses. — Great care miist be exercised in replacing fuses for reasons explained later under Chapter XII, "Dangers Involved in the Use of Electricity." The entrance switch should always be opened if possible when any branch fuse is being replaced, and if the main fuses blow, you had better have an electrician replace them im- less you have become thoroly fa- miliar with the points described in the chapter mentioned. Whenever replacing fuses, it is well to use only one hand and to keep the other away from Fuse Blaclta Fig. 37. Showing a very sat- isfactory arrangement of en- trance switch and fuses for use in houses. The switch is en- closed. When the switch is in the oS position, the branch- circuit fuses can be replaced without danger. anything of metal connected to the ground. Summary of Principles in Chapter VII 1. Fuses are safety devices placed in an electric circuit for the purpose of protection. 2. Fuses have in them a piece of metal known to be able to carry only a certain amount of current without melting. 3. Fuses are placed in every main circuit in a house and often in many of the branch circuits. 4. Great care should be exercised in replacing fuses. Questions 1 . Why is it important to know what fuses are? 2. What are fuses used for? 3. What might happen if the fuses were omitted in a circuit? 4. Describe the plug fuse. 58 PRACTICAL ELECTRICITY FOR BEGINNERS 5. What happens when a fuse "blows?" 6. What kind of fuses are commonly used in automobile lighting systems? 7. Where are the fuses usually placed in the main circuit in a housed 8. What are branch circuits? 9. What are the advantages of having fuses in branch circuits? 10. How are fuses tested? 1 1 . What must be borne in mind when replacing fuses ? Suggestions 1. Procure a fuse and examine it carefully. 2. Try as many of the methods of testing a fuse as you can. 3. See if you can locate all of the fuses in your house. 4. See if you can locate the fuses on your automobile. 5. Remember that it is quite easy to get a shock while replacing fuses and be sure that you are perfectly safe before touching them. b. Study the dangers involved in replacing fuses very carefully when you get to that part of this book. CHAPTER VIII Heater-Circuit Troubles; How to Detect and Remedy Them 54. Complete Heater Circuit.— To understand all of the possible heater-circuit troubles, let us consider the manner in which current is usually transmitted from the power lines to the heating element. The terminals of the heating ele- ment are attached to pieces projecting out thru the heater frame. On these, an attachment is pushed which makes con- Ploj Fig. 38. Diagram of the connections in a heater circuit. nections between the heater terminals and the wires in an ex- tension cord. In the extension is sometimes placed a port- able switch. The ends of the extension cord are connected to a plug. The plug is screwed into a receptacle, and the recep- tacle is connected to the wires upon which the electrical pres- sure is impressed. Each of these will be described briefly. These connections are shown in Fig. 38. 65. Attaching Cord Used With Heater. — Fig. 39 shows an attaching cord for a heater circuit, the appearance of which is familiar to many readers. To use this cord, the attachment B is pushed into place on the heating device, This attachment has two openings in it which, when in place, 59 60 PRACTICAL ELECTRICITY FOR BEGINNERS fit over two projecting pieces of metal on the heater. These pieces are the ones to which the heating-element terminals are connected. C is a switch which is used to turn the cur- rent on or off. The cord contains two flexible wires covered with rubber and then with silk or cotton. A is a plug which is screwed into a receptacle provided for a current outlet, usually in a convenient place in the wall. 56. Wall Receptacle Into Which Plug Is Screwed.— AHachmeni The receptacle, into which the plug on the end of the cord is screwed, consists of two distinct metallic parts separated from each other by some insulating mater- ial, usually porcelain. The rv„ on rpi. 4.* v j oue metallic part is in Fig. 39. The attaching cord *^ commonly used with a heater, the bottom of the receptacle, The switch is omitted in many . ^, ,, . . ,, , cases. and the other is m the form of a thin sheet around its side. One of the wires from the source of current is connected to the bottom piece, and the other to the side piece. 67. Extension-Cord Plug. — The plug A (Fig. 40), which fits into the receptacle, consists also of two metallic parts insulated from each other — one on the end of the plug and the other on its side. These two parts are connected to the two wires in the cord. When this plug is screwed far enough into the receptacle to bring the metallic end in con- tact with the piece in the bottom of the receptacle, the line wires are connected to the wires in the cord. These wires form a conducting circuit, thru the switch, to the metallic HEATER-CIRCUIT TROUBLES 63 pieces in the heater attachment. Fig. 41 shows another type of plug which is very convenient. 68. Connections Made by Extension Cord. — When the attachment is pushed into place on a heater, and the plug on the end of the attachment cord is screwed into a recep- tacle, about twelve different connections are put into play. There is always a possibility that one or more of them will gradually become loose or disconnected, which, together with others to be described later, may be the cause of the failure of a heater to function properly. - Connector' 69. Possible Heater - Circuit Troubles. — ^AU of the possible causes of the failure of a heater to heat up properly may be summed up as follows: 1. The e3ctension-cord plug may not be screwed into the receptacle far enough to bring the two metallic pieces in con- tact. 2. A fuse may have been blown. 3. The power may be shut off. 4. The heater terminals may be dirty or burnt off, and may not come in contact with the metallic parts in the attach- ment. 5. The metallic pieces in the attachment may be dirty or burnt off, and may not come in contact with the heater terminals. 6. The coimections to the metallic pieces in the attach- ment may be poor, or strands of the two wires may be touch- ing each other. Fig. 40. The parts of a plug commonly used on the end of an extension cord. 62 PRACTICAL ELECTRICITY FOR BEGINNERS 7. The connections to the switch may be poor. 8. The connections to the metallic pieces in the plug may be poor, or strands of the two wires may be touching each other. 9. One of the cord wires may be broken. 10. The ends of the heating unit may be disconnected from the heater terminals. 11 . The heating element may be burned out. 60. Plug Trouble and Remedy.— The plug on the ><-B ^ — ^""Srfrrrh ^^'^ °^ ^'^ extension cord I B^m ( ■ ■ 1 - \\n\l "^^y °°^ ^^ screwed into 1 r^^ y y Mil) I ^'^ receptacle far enough ^^ — £^-B to bring the two metallic pieces together. If the heater does not heat up, it is best to try the plug to make sure that it is screwed into the receptacle properly. In case of a short circuit, strands of the wires in the plug may be connected, in which case they should be separated and fastened firmly. 61. Detecting a Blown Fuse. — ^A blown fuse may be the cause of the failure of a heater to operate. If there is only one fuse block at the entrance — ^that is, only two fuses- one can readily trace the trouble to a blown fuse, or to the lack of power, when a power company is sometimes com- pelled to shut down, by turning on the lights some place in the house. If they light, there is no lack of power. If, how- ever, there is more than one set of fuses — ^that is, more than one circuit — the following may be done: Remove the plug on the end of the heater cord from the redeptacle and place a Fig. 41. Another type of exten- sion-cord plug -which can be removed and replaced without turning the threaded portion out of the recep- tacle. HEATER-CIRCUIT TROUBLES 63 lamp in its place. If the lamp fails to light, but the lamps at other places in the house do, it is quite likely that one, or both, of the fuses in this particular circuit has been blown. In this case, it is necessary to replace the burnt-out fuse, or fuses. To do this, go to the place where the main switch is, open it, and follow the instructions imder Sec. 53, Chapter VII. After having replaced the blown fuse, try the heater again, and if it fails to work, test with a lamp again. If the lamp lights wp, it is certain that current is available at the receptacle and that something else is causing the trouble. (See Sec. 84.) 62. Heater-Terminal Defects, — The heater terminals may be burnt off or dirty, and may not come in contact with the metallic parts in the cord attachment. To detect this trouble, remove the attachment and examine the terminals on the heater. They should be clean and bright and long enough to reach well up into the attachment. If they are dirty, they can be cleaned off with a knife, but if they are burnt off, it is diflBcult to repair them. The burning of these terminals is caused by removing the attachment from them while the ciirrent is turned on. Therefore, to avoid it, al- ways be sure that the current is turned off before the attach- ment is removed. If these terminals are burnt beyond re- pair, it is usually possible to purchase new ones from dealers handling the particular heater so burned. 63. Attachment Troubles and Remedies. — The met- allic pieces in the attachment may be burnt off or dirty so they do not make a connection with the heater terminals. (See Fig. 42.) To detect this trouble, remove the plug from the receptacle and the attachment from the heater and re- 64 PRACTICAL ELECTRICITY FOR BEGINNERS move the small bolts that hold the latter together. It will come apart then and the condition of these pieces can be de- termined. If they are dirty or bent, they can be repaired, but if they are burnt off, new pieces will be required. These can be purchased from a dealer handling the particular kind of heater being used, or directly from the company manufac- turing it. These, too, are burnt when they are removed from the heater while the current is flowing thru them. Therefore, to rj[^^ avoid trouble, be sure to turn the current off be- X.. .. •i=i''"Ow fore removing the at- Ineatare sometime? /^^^ -''D^^ burnad off y^ tachmeut. The placing of a portable switch in attechmlir^ ^'''^ °* ^ '°"""°" ''*^*" tl^e cord makes this very convenient. While these metallic pieces are bemg inspected, it is well to see that the wires attached to them are held firmly imder the screw- heads and that they are entirely separated from each other. Connection between these wires would cause a short circuit. 64. Other Possible Troubles.— If none of the tests de- scribed solve the heating problems, all parts of the circuit should be examined for loose connections or broken connec- tions. If short circxiits are formed, as might be the case, the fuses will be burnt out as fast as they are replaced, until the short circuit is removed. It is well, if other tests fail, to re- move the heater cover and to examine the connections of the heating element to the terminals. They may be loose or broken. If none of these solve the mystery, it is quite prob- HEATER-CIRCUIT TROUBLES 65 able that the heater is burnt out. 65. Burnt-Out Heating Element. — In selecting the material for the element of a heater, it is very difficult to find a material that will not burn, to some extent at least, when it becomes very hot, and, altho great care may be taken in the selection of heating-element materials, there is always a pos- sibility of their burning out. If this does occur, the heater will fail to operate and none of the foregoing tests will locate the trouble. This will be detected only by removing the ele- ment from the heater. If it is found to be burnt out, it must be replaced with a new one, which can usually be purchased from a dealer or from the company manufacturing the par- ticular heating device in question. SureiARY OF Principles in Chapter VIII 1. Troubles in heater circuits are auite likely to be due to poor connections, burnt terminals, or short circuits. 2. Remedies for most troubles are simple and easily applied- QUESTIONS 1. How is current transmitted from the line wires to the element of a heating device? 2 . Describe the attachment cord used with a heater. 3 . What is a wall receptacle ? 4 . What is an extension plug used for ? 5. What trouble may exist in an extension-cord plug? 6. How do you detect a blown fuse? 7. What may be wrong with a heater terminal? 8. What in a heater attachment may cause trouble? 9. How can these troubles be remedied ? 10. What other troubles might be found in the circuit? 66 PRACTICAL ELECTRICITY FOR BEGINNERS 11. How can the burning of the heater terminals be avoided? 12. What is the advantage in using a cord with a switch in it? 13. What must be done if a heater element is found to be burnt out? Suggestions 1. Procure a heater cord that is connected properly and remove the plug, noting carefully just how it is attached. 2. Reconnect the plug to the cord as you found it. 3. Do the same with the attachment. 4. Connect up a new cord as soon as one is needed. 5. Try as many of the tests described in this chapter as you can. 6. Observe carefully all of the heating circuits you may have an opportunity to inspect, and see if you can figure out just why the de- fects listed would cause the heater to fail to operate, and how you would detect and remedy them in each particular circuit. CHAPTER IX Incandescent Lamps and Their Use 66. Electric Lamps. — Electric lamps are devices de- pending upon the heating effect of electrical current for their operation. Incandescent lamps are used so extensively at the present time that they are quite common. In fact, prac- tically every automobile is equipped with them; nearly all modem homes use electric lights exclusively, and street cars, interurban cars and steam railway passenger cars, and even streets, are lighted by them. Their use is so extensive even at the present time that hardly a day passes during which the average i)erson does not make use of them. It is not necessary, then, more than to mention the fact that every- body should know something about electric lamps and their use. 67. Principles of Incandescent Lamp.— Let us con- sider, then, the principles involved in the making of the in- candescent lamp. It has been shown that whenever elec- trical current is forced thru a conductor, heat is generated and that the amount of heat so generated depends upon the resistance offered by the conductor and the amount of cur- rent forced thru against this resistance. Then, too, it has been shown that the resistance of a conductor depends upon the material of which it is made, the diameter or cross-sec- tional area, and the length. Everybody is familiar with the applications of the principles in heating devices. The electric lamp is another device based upon the same principles, its purpose, however, being to give off light instead of heat. liqht\ 68 PRACTICAL ELECTRICITY FOR BEGINNERS 68. Why a Lamp Gives Off Light. — Every reader is no doubt familiar with the fact that certain materials, especially metals, give off light when they are heated to a high tempera- ture; that is, a piece of iron whittt hot or steel will become red hot or _~ ^^J ' '/^ white h ot if its temperature is •^ Bil^J****^^^^^^" raised high enough (Fig. 43). Borof steeiX When a material becomes hot , . . /Y. T 1 . • . 1 • Fig. 43. Illustrating how light enough to give off light m this is given ofif when a bar of steel is manner, it is said to be mean- ^^""^^^ ^^"^ ^°^- descent, and it is from this that the lamp gets its name "incan- descent lamp." The conductor inside of the lamp bulb becomes so hotthatit is incandescent, or gives off light. Of course, nearly all materials give off light when they bum, but it must be under- stood that it is not necessary that all of them bum before they are capable of doing so. 69. Lamp Filament and Bulb. — ^AU common materials l^cTrr Two commoETforms ^ave a tendency to melt when of carbon filaments. they get hot, and most of them burafreelyifplentyofairispresent. Knowing,then,thatcertain materials give off light when they are heated to an extremely high temperature, it will be quite readily understood that if electrical current were forced thru a conductor of very high resistance, it would be possible to cause the conductor to give off light, providing it is capable of withstanding the very high temperature without melting or burning. It will be clear, also, that the conductor would necessarily have to be limited in INCANDESCENT LAMPS AND THEIR USE 69 fl ps..i .' n I - CoMonPluf TO F.l«..< ^i m % w «/... /^Br«»5 Tip Fig. 46. Sketch of a lamp base showing the manner in which the electrical current is led into and out of the lamp filament. length and that its diameter would have to be made very small if the desired results were to be obtained. With these points in mind, the following discussion will be readily understood: In incandescent lamps there is a fine wire called a filament which is heated white hot by an electric current. The light emitted is the same as it would be if the filament were heated in some other manner. In early experiments, platinum was tried for the filament, but even tho it melts only when it has reached a tem- perature about sijcteen times that of boiling water, it could not stand the re- quired temperature. Carbon is one of the few known substances with a higher melting point, and in 1880 Edison and others succeeded in making a lamp with a carbon filament, two forms of which are shown in Fig. 44. Since the filament would bum up at once if there were any air present, it had to be placed in a glass bulb, out of which the air had been exhausted. 70. How Current Gets into Lamp Filament. — The electricity is led into and out of the filament thru two short platiniun wires melted into the glass bulb at one end. (See Fig. 45.) These platinum wires are connected by copper wires to the brass collar and metal tip at the base of the bulb. This base, when screwed into the receptacle or socket, makes con- nection with the power wires. The turning of the lamp into the socket is the equivalent of connecting the line wires to the ends of the filament. 70 PRACTICAL ELECTRICITY FOR BEGINNERS 71. Metallic Filaments. — ^Metallic filament lamps (Fig. 46) have rapidly supplanted the old carbon filament ones during the last few years, and are, perhaps, most popular at the present time. These filaments are made of tungsten and of tantalum. Both of these metals have melting points higher than that of platinum, but their resistance is consider- ably less than that of carbon. This necessitates the use of a filament much longer and finer than the one used in the old carbon filament lamps, but filaments of this kind give a much whiter light, and they do not use as much power as the carbon ones. The long filaments required in these lamps are woimd zigzag on a star-shaped reel. One difiiculty with these metallic filaments is their liability to breakage because of their brittleness, but vast improvements have been made recently, and today they are quite satisfactory. 72. Gas-Filled Lamps. — Gas-filled lamps are replacing ordinary metal-filament lamps in some places at the present time, and may be- Metaliic "fil- come more popular in the very near future. In ament lamp. ^^^ ^^^ filament is short and the bulb is filled with a gas, usually nitrogen, where in other bulbs there is nothing. These lamps give more light than the others on the same amoimt of power. They are used quite extensively in street-lighting and, in a few cases, in house-lighting, but the smaller sizes are, as yet, not very satisfactory. There still remains plenty of chance for improving incandescent lamps. 73. Wattage Marks on Lamps . — ^Altho no attempt will be made at this time to explain what is meant by a "watt," it is well to mention that the wattage of a lamp, or the number INCANDESCENT LAMPS AND THEIR USE 71 of watts by which the lamp is designated, is the measurement of the amount of power required to make the lamp "burn" — that is, a 60-watt lamp takes four times as much power as a 15-watt one and is four times as expensive to operate. Of course, it gives off more light also. (See Chapter XI.) Summary of Principles in Chapter IX 1. Electric lamps depend upon the heating effect of electrical current for their operation. 2. The filament in a lamp has a very high resistance and a very high melting point. 3. The air is exhausted from a lamp bulb to keep the filament from burning up. 4. Gas-filled lamps have their bulbs full of gas which for some reason makes them give off more light. Questions 1 . Why is it important to know something about electric lamps 7 2. Upon what principles of electricity is the electric lamp based 7 3. Who invented the incandescent lamp 7 4. How is current led into a lamp filament? 5. What are the advantages of metal-filament lamps over carbon ones? 6. What are the disadvantages, if any? 7. What are gas-filled lamps? 8. What does the wattage mark on a lamp represent? 9. What is the difference between a 16-watt lamp and a 60-watt one? Suggestions 1. Observe carefully any electric lamp you may see and try to trace the path of the current thru it. 2. Try different kinds of lamps at the same time and observe their differences. That is, connect a carbon, a tungsten and tantalum lamp in the same circuit or put them in the same fixture and note their differences. 3. Look for the wattage number on any lamps you may see and note their brilliancy and the size of their filament. This is usually printed on a small sticker near the base of the lamp. 4. Try connecting up any lamp circuits for which you may be able to secure the required materials and equipment. CHAPTER X The Opekation of Electrical Lamps 74. Importance of Being Familiar with Lamp Oper- ation. — Electric lamps are used to so great an extent in the home that a description of the possible troubles commonly encountered should be of interest to everyone. Many occa- sions arise where considerable inconvenience and expense are Fig. 47. A shows a common lighting installation. B shows one set of connections involved in this installation. C shows another method of connecting in the fixture. D shows the simple diagram of the con- nections. brought about by some simple troubles which might easily be detected and remedied by anyone familiar with them. It is not intended to tell, at this time, how to wire a house or how it is wired, but simply to bring out the simple principles and to show how to detect and remedy common troubles which cause a lamp to fail to operate. 76. Complete Lighting Circuit. — Let it be understood at the beginning that there must always be two complete THE OPERATION OF ELECTRICAL LAMPS 73 conducting circuits between every lamp and the source of current. Connections may be made thru switches, fixtures, sockets, plugs, extension cords, lamp stands, or other con- venient apparatus, but they must be made properly before the lamp will light up (Fig. 47). There is always a chance for some little thing to happen to any of these which may keep the current from passing thru the lamp filament, and it is, in some cases, these little things that cause most of the troubles in house-lighting. 76. Possible Lighting-Circuit Troubles. — Bearing the foregoing in mind and recalling the simple facts regarding electrical circuits, it will be seen that if a lamp is screwed into a lamp socket or receptacle, and it fails to light up, any of the following may be the cause: (1) The lamp may not be screwed into the socket far enough, (2) the lamp may be burnt out, (3) the switch may be open or disconnected, (4) a fuse may have been blown, (5) the power may be shut off, (6) the connections inside of the socket may be poor, (7) the wires in the fixture may be dis- connected ; or, in the case of a table lamp or floor lamp where an extension cord is xised, (8) the extension cord plug may not be screwed in far enough, (9) the wires in the plug may be disconnected, (10) the cord wire may be disconnected in the lamp fixture. 77. Lamp Not Turned In Far Enough. — It is very easy to understand that the lamp must be screwed into the socket far enough to bring the metallic piece on the end of its base in contact with the piece in the bottom of the socket (Fig. 48). The remedy, then, is to turn it in farther. It 74 PRACTICAL ELECTRICITY FOR BEGINNERS >ro*» SUM BniM sometimes bapi)eiis that the small piece of brass A in the bottom of the socket becomes bent down, and it is impossible to bring the two pieces in contact, however hard the lamp is turned. If this should happen to be the case, open the smtch and pry this little piece up with a knife or screwdriver. (If the switch is not opened, you will undoubtedly blow a fuse by making a coimection be- tween this little piece and the brass shell inside of the socket which will cause a short cir- cuit, the current going thru the knife or screwdriver.) 78. Burnt-Out Lamp. If the lamp is turned in tight- ly and a connection is made. Fig. 48. The interior of a com- mon lamp socket. The dark areas show the path of the current. but still refuses to light, it may be burnt out; that is, the fila- ment may be burnt or broken. To determine whether or not this is the case, try a different lamp in the same socket or hold it up to the light and examine the filament. Sometimes, if there is only a single break in the filament, it is possible to weld the ends together by giving the lamp a gentle tap while the current is on. 79. An Open or Disconnected Switch. — Sometimes there is more than one switch in a lamp circuit, as in the case where several lamps are suspended from one fixture to make possible the operating of any or all of them (Fig. 49). One should be certain that both the wall switch and the key switch in the socket are closed. A push-button switch is closed when the white button is pushed in, and a key switch THE OPERATION OF ELECTRICAL LAMPS 75 usually snaps as it is turned off; that is, it gives a sort of a click when it is turned off and makes no sound as it is turned on. The key usually turns a little harder when turned on than when turned off. U Fig. 49. A common installation. The wall switch controls both lamps, and the key switches control them individually. A diagram of the connections is given also. If the wall switch is disconnected, or if the connections to it are loose, it is possible that closing a door or jarring the switch in any way may cause the lamps on Its circuit to go out or to flicker. In such a case, remove the switch cover and fasten the wires firmly under the screws in the switch termi- nals. These wires are in plain view, and this adjustment can be made very easily without danger. If the wall switch is found to be all right, and the key switch tmned on, and still the lamp refuses to light when placed in the socket, and if there is only a single socket, the fault may be that listed in No. 6, Sec. 76. If, however, the fixture into which the lamp in question has been placed is for more than one lamp, try the other sockets in the same fix- ture. If the lamp lights in any of them, the fault must be No. 6. If it fails to light in any of them, the trouble may be that listed No. 7. 76 PRACTICAL ELECTRICITY FOR BEGINNERS 80. A Blown Fuse or Lack of Power.— If there is only a single circuit in a house, one set of fuses, and none of the lamps light up when their switches are closed, either a fuse has been blown or the power has been turned off. If any lamp in the house lights, when there is only the one set of fuses, these cannot be the causes of the trouble (Fig. 50, A). eo n rt Fig. 50. Testing for a lack of power or a blown fuse. A represents a simple entrance switch arrangement, and B an arrangement providing for two circuits. The fixtures are supposed to be in different rooms of the same house. If the lamp lights as shown with arrangement A, the fuses are all right. If with arrangement B, one of the branch fuses may be blown. If, however, there is more than one fused circuit in the house (Fig. 50, B) and the lamps on one circuit light, but none on one of the others, it is almost a sure indication that at least one fuse has been blown. If a blown fuse is detected and re- placed, take special care to see that it does not blow again as soon as the switch is closed. If this happens, a short circuit is causing the trouble and must be taken care of before put- ting in a new fuse will do any good. 81. Poor Connections in a Socket. — If there is only a single socket on a particular circuit and all previous tests have failed to reveal any fault, the trouble is quite likely to be within the socket itself. It will be necessary, in such a case, to open the switch in the wall, or, preferably, the main THE OPERATION OF ELECTRICAL LAMPS 77 switch, to remove the socket cover, and to look for loose con- nections. If, however, more than one socket is placed at this particular place and a lamp will light up in none of them, the fault is most likely to be that listed under No. 7, Sec. 76. If the lamp lights in all of the sockets on a fixture but one, the fault must be in the socket or its connections. 82. Faults in a Fixture. — If several lamps are provided for on one fixture and none of the sockets will furnish current to a good lamp, it is most likely that the wires in the fixture have become disconnected or burnt. This occurs very rarely, however, except in cases where heaters are connected to lighting circuit outlets. Sometimes the wires in the fixture are not large enough to carry all of the current required by a heater, and they are burnt out. It is for this reason that special receptacles should be provided for heaters. If this appears to be the cause of the trouble, examine all of the easily-accessible joints in the fixture first, and, finally, those imder the canopy, or other arrangement, on the ceiling or wall. These joints will be found to be soldered and cov- ered with tape, but a break can usually be detected by pulling gently on the wires without removing the latter. 83, Other Possible Troubles. — If none of the foregoing tests reveal the difficulty, it may be that — in such cases as table-lamp and floor-lamp installations — extension-cord con- nections are poorly made or have become loose, or that the connections within the lamp-stand are poor. If this is sus- pected, apply the tests to these in the same manner as ex- plained in the discussion of heating circuits and in the first part of this chapter. 78 PRACTICAL ELECTRICITY FOR BEGINNERS 84. Short Circuits. — The foregoing tests and remedies properly applied in the order given should ordinarily take care of the problems arising in the average home. There is, how- ever, the possibiUty of forming a "short" in a circuit (Fig. 51), which causes the blowing out of a fuse or fuses. This has r» been mentioned ^ _ A _. imder the study of heating and in Sec.61,butneeds a more extended description and explanation at this time. Short circuits which usually result in the blowing of fuses. Accidental con- FlG. 61. Five possible causes of short circuits: 1. Touching of bare wires entering a lamp. 2. Wire not wrapped around connector on end of ex- tension plug. 3. Wires touching inside of an ex- tension-cord plug. 4. A nail, screwdriver or the like in a socket or receptacle. 6. Loose or poor connections in a socket. may be caused by any of several conditions, nections may be made by loose connections in a socket, making it possible for two wires to touch each other; by wearing off insulation; by breaking of insulating material, or anything else which would make possible an easy path for the elec- tricity. If a short circuit has been formed, the fuses will be blown as fast as they are replaced. It is possible that some of the lights are all right when, suddenly, just as a switch is closed or a lamp turned on, they all go out. This indicates that there is a short circuit in that particular part of the line, and it must be left open or the short removed before it would do any good to replace the fuses. If this should occur after dark, and it is desired to use the THE OPERATION OF ELECTRICAL LAMPS 79 lamps that night or to postpone the removing of the short circuit, it is necessary only to leave the one circuit open and to put in a new fuse. 7/ aftise must he placed in a circuit at night when all of the lights are off, light a match or candle before mak- ing an attempt to remove or insert it. More than one person has received a severe shock while trying to replace a fuse in the dark. (See Chapter XII.) \h\ I m 1 ^ 'M' Fig. 62. A Ulustrates an installation with a short circuit in one branch and the proper arrangement for testing for it; B, the lighting dimly of the test lamp and the one in a good circuit; C, the lighting brightly of the test lamp and the failure of the lamp in the defective circuit. 86. Tests for Short Circuits. — It is not always possible to detect the location of a short circuit as easily as has been indicated, in which case it will be necessary to test for it. The author believes that the following method used by him is as satisfactory as any, and it is very simple and inexpensive. This explanation is for a single circuit installation, but can be applied in any circuit. Open the entrance switch and remove the fuses, replacing them with one good fuse and an ordinary lamp. Close the main switch and turn on, one by one, every branch of the cir- 80 PRACTICAL ELECTRICITY FOR BEGINNERS cxiit, noting the brilliancy of the lamp on that branch. (If there is only a receptacle in some branches, turn a lamp into it.) On every branch circuit that is all right, the lamp, or lamps, will light up dimly, as will also the one in the fuse receptacle. When the circuit in which the short has been made is reached, the lamp in the circuit will not light up, but the one in the fuse receptacle will light up brightly (Fig. 52). After the circuit in which the short has been formed has been located, the main switch should be opened and all parts of the apparatus in the circuit inspected for possible shorts such as broken parts, worn insulation, etc. The short circuit can be removed by tightening down loose wires, replacing broken parts, covering bare wires with friction tape, or what- ever else may be necessary. 86. Value of Tests and Remedies. — If all of the fore- going tests and remedies are studied carefully and applied properly, there is no reason why every house owner cannot be his own electrician. It is important that every person be able to do this kind of work because of the expense and incon- venience involved in being compelled to hire someone else to doit. Then, too, considerable time is frequently lost in waiting for some little repair job that can be taken care of without cost and with very little trouble by some member of the family. Summary of Principles in Chapter X 1. Lighting troubles are quite likely to be due to poor connections or short circuits. 2. Troubles are easily detected and remedied. the operation of electrical lamps 81 Questions 1. Why is it important that everybody be familiar with lighting operations? 2. What apparatus is involved in the average lighting circuit ? 3 . Enumerate the possible lighting-circuit troubles. 4. Why is it that failure to turn the lamp into the receptacle far enough may cause it to fail to light? 5. What may be wrong in a lamp receptacle? 6. Why is it necessary to open the switch when working on a lamp receptacle or socket? 7. What causes a lamp to burn out? 8. How can a burnt out or broken filament be detected? 9. How is it possible, sometimes, to repair a broken filament? 10. How can you tell whether a switch is on or off? 11. If a fuse blows just as soon as it is replaced, what is the trouble? 12. How are poor connections in the socket detected? 13. What may be wrong in the fixture? 14. What are short circuits? 16. What happens when a short circuit is formed? 16. How is a short circuit detected? 17. How is it repaired? 18. What should be done if a fuse must be replaced at night? 19. How is it possible to use part of the lamps in a house even tho there is a short circuit in some one circuit? Suggestions 1. Try as many of the tests described in this chapter as you possibly can. 2. Try to repair a broken lamp filament. 3. Many times just before the filament in a lamp burns, the inside of the bulb becomes partly covered with a sort of dark substance. See if you can notice this on any lamp and watch it to see how long it lasts after this begins to appear. Ifoofc H I|l | l | i|l [ l| l| l| HM l|i ] i | l|l|i|l | '| l |l l '|'l' CHAPTER XI Electeical Measurements 87. Necessity of Units.— So far in oiir discussions we have spoken in a rather general way about electrical quanti- ties, and such terms as volts, amperes and watts have been used more or less indefinitely. An attempt will be made at this time to give suflScient description of these units to afford the reader a working knowledge of them at least. Many of the common units of measurment such as the cent, nickel, dime, quarter, half-dollar and dollar, \ised in specifying values, and the inch, foot, yard and mile, used in specifying lengths, are so familiar to most of lis that we seldom stop to Fig. 53. Examples of common units of think and to real- measurement. ize that they really are imits of measurement (Fig. 53). Suppose, for an instant, that we had no such imits. We would be compelled to use such statements as "a bushel of potatoes is worth quite a lot; a yard of cloth is worth a little more; a house and lot are worth many times as much," and so on, without being able to measure the value or to tell anyone else what it is. Then, too, in trying to express length, we would have to use such expressions as long, longer, short, etc., and it would be almost impossible to make these measurements at all definite. To do away with any such inconveniences, various units of measurement have been established which are a standard ELECTRICAL MEASUREMENTS 83 used by everybody in this country and in some of the foreign countries, the unit of value being the dollar, and the unit of length the foot. It is just as necessary to have units of measurement for electrical applications as it is in any others, to make possible the definite measurement of values. The more common of these will be discussed from a practical standpoint with spe- cial stress placed upon their use rather than their origin. en H DRV ctu. STOR/l»e. B/ITTBRY v Fig. 64. Two common sources of electrical pressure and diagram- matical water pressures of similar values. 88. Common Electrical Units. — The most common units used in electrical work are the volt, the ampere, the watt, the kilowatt and the kilowatt-hour, while some of the less commonly used ones are the ohm, the farad, the maxwell, etc. We are more particularly interested in the first four, because they are used so commonly, and we shall limit our discussion to them alone. 89. The Volt. — The volt, with which we are somewhat familiar in a general way, is the unit by which electrical pres- sures are measured. Whenever voltage is spoken of, elec- trical pressure is referred to. Common voltages are: dry cell, 1.5; a storage cell, 2; common lighting and heating cir- cuits, 110; common power circuits, 220 or 440; and many street-car circuits, 550. 84 PRACTICAL ELECTRICITY FOR BEGINNERS We have learned that the voltage mark on any piece of electrical apparatus is placed there so the user will know the pressure upon which it is supposed to be used. The voltage applied may be less than that given on any electrical device, but it should not be more. For instance, many lamps or flat- irons have a 118-Vor a 120-Vmark on them. They are ex- pected to be used on 110-volt circuits and are made this way so that if the pressure, which is, in most cases, furnished by a generator, becomes a few volts too ammtur \ j high, the apparatus being used will not be burnt out. 90. Measuring Volts. — Because of the fact that most electrical pres- sures are standard ; that is, 1.5, 2, 6, *"* " 110, 220, etc.; it is not usually nee- neSing^voUme?er1 Tnd ^ssary to measure voltages except in ammeters in electrical cir- special work. It is known that the cults. voltages of cells are added when the cells are connected in series so they can be calculated without difl&culty. If, however, it becomes necessary to measure the voltage of a battery or generator, all that is required is to con- nect the terminals of a meter, known as a voltmeter, to its terminals or to wires running from them, in a manner some- what similar to that of connecting a bell or lamp to a line. (See Fig. 56.) 91. The Ampere. — It is a little more difficult to understand just what is meant by an ampere because the ampere is the unit of rate of flow of current, but a brief description will probably make the term sufficiently clear. ELECTRICAL MEASUREMENTS 86 __ei The ampere is the unit by which we express how fast electricity is flowing in a circuit; that is, if one bell requiring a certain amount of electricity is connected to a battery, the electricity will have to flow thru the wire fast enough to keep the bell fully supplied, or it will not ring. The speed or rate at which it flows is expressed as so many amperes. Now, if a second bell of the same type is con- nected to this same battery cir- cuit, it is evident that in order to "feed" enough electricity to both bells to make them ring, the current would have to be twice as great; that is, the electricity would have to ± ^ Pig. 55. Illustrating the flow of current thru a circuit containing one lamp, and thru a circuit containing two lamps. Also similar cases in the flow of water. flow out of the battery twice as fast or the amperage would be twice as much. Fig. 55 shows this with lamps instead of bells. Taking a definite example, it is known that an ordinary mediimi-sized lamp requires about 1/2 ampere flowing thru its filament to make it light up. Now, suppose that there are three lamps connected to one fixture into which two main wires run. The current must be flowing in these wires at the rate of three times 1/2 or 1-1/2 amperes. 86 PRACTICAL ELECTRICITY FOR BEGINNERS 92. Measurement of Amperes. — It is impossible to determine amperes in a manner similar to that used in deter- mining volts, because the rate at which current flows in a cir- cuit depends upon the pressure and the resistance offered by the circuit. It should be remembered, however, that an ordinary 110-volt lamp of medium size requires about 1/2 ampere, and that the total number of amperes required by several such lamps on one circuit will be the number of lamps multiplied by 1/2. On heating devices, the number of amperes taken is marked on the name plate. Thus, a mark of 4.9 on a flatiron means that the flatiron will draw 4.9 amperes when connected to a pressure of the value also stamped on the name plate: that is, a 110-volt, 4.9-amp. iron will draw 4.9 amperes when con- nected to a 110-volt line. Fuses, as we already know, are stamped with a numeral representing the number of amperes they are capable of car- r3nng without "blowing." The sum of all of the currents being drawn at any one time thru a set of fuses must never add up to more than the capacity of the fuses. For example, suppose that in a house where there is only one main circuit protected by 10-ampere fuses, a heater drawing 6 amperes is being used, and that an attempt is made to use a 4.9-amp. flatiron in some other room, or on some other branch circuit at the same time. The total number of amperes that would have to pass thru the fuses would be 6 plus 4.9 or 10.9. Now, the fuses will carry only 10 amperes, so as soon as the attempt to use the iron is made, they will blow. This, of course, would shut the heater off also, and it would not operate again until the fuses had been replaced. There would be a great ELECTRICAL MEASUREMENTS 87 advantage in having the fuses blow in such a case, however, and it is for such cases that they are of great value, because the large amount of current, 10.9 ampere, might be suflScient to bum the insulation off of the main wires in the house and to set it on fire. When large amoimts of current must be used, special provision must be made by installing branch circuits and larger main wires. When it is necessary to measure how fast current is flowing in a circuit, a meter known as an ammeter is used (Fig. 56). It is connected in the circuit in the same manner as a push- button is connected in a bell circuit; that is, in series. The most common use of the ammeter in every-day applications is in the automobile where it is placed on the dash and con- nected in the storage-battery circuit to give a reading of the number of amperes flowing into or out of the storage battery. 93. Watts and Kilowatts.— The watt is the unit by which power or ability to do work is measured. It may seem strange that neither volts nor amperes give a measure of power, but neither does. The amperage of different pieces of apparatus on the same circuit give an indication of the power, but not the actual power. A brief description will make this more readily \mderstandable, I believe. Suppose that a large steel tank is partly filled with water and air that is forced into it imtil the pressure is very high. Now, if the tank is completely closed, the pressure would re- main there indefinitely, but it alone would be of no particular value in so far as power is concerned. The only manner in which it coiild be made serviceable would be to drill a hole in it and attach a pipe to the tank and permit the water to flow out. The flowing of the water under the pressure would do 88 PRACTICAL ELECTRICITY FOR BEGINNERS work if proper arrangements were made for using it, and the power it would have would depend upon the speed at which the water was permitted to flow out. It will be seen that two things are necessary for power — ^pressure and the flow of the water. In electrical work, the same is true. There may be any amount of voltage, but it alone does not represent power. Electricity must flow before it is capable of doing anything, and the faster it flows, the more it is capable of doing. It is evident, then, that volts and amperes combined are necessary for a measurement of power because the voltage is the meas- ure of the pressure and the amperage is the measure of the rate at which the electricity flows. Since in ordinary uses the nimiber of watts of power deliv- ered to a circuit is so large that it might run up into figures which are inconvenient to handle, the imit more commonly used is the kilowatt, which is equal to 1000 watts. 94. Measuring Watts and Kilowatts. — The number of watts of power required by a lamp is usually printed on a small piece of paper attached to the base, or near the to base. A lamp marked "60-watt" requires foiir times as much power as one marked "15-watt," and, consequently, costs four times as much to operate. Lamps are ordinarily distin- guished by their wattage; that is, we speak of 15-watt, 40- watt, 60-watt and 100-watt lamps. These numbers are the measure of the power required to operate the lamps or the power used by them when they are operated. Ordinarily, it is not necessary to know how many watts are required for the operation of a piece of electrical apparatus unless it is desired to determine its cost of operation. If it is ELECTRICAL MEASUREMENTS 89 desired to know the power required by heaters and the like, the number of watts can be determined by multiplying the volts by the amperes. For example, if a heater is marked "110-V — 5-amp.", the number of watts it would use when connected to a 110-volt line will be 110 x 5, or 550. If this were to be expressed in kilowatts, it would be 550 divided by 1000, or .55, or a little over 1/2 a kilowatt. When it is necessary to measure watts, an instrument known as a wattmeter is used, but in common applications, its use is very limited. 95. Kilowatt-Hours. — Upon careful thought, it will be seen that none of the foregoing units take into consideration the length of time power is used. This may not be clear, but consider the following: A man may be ever so strong and powerful, but his value is measured by the length of time he uses his strength to an advantage; that is, if someone hires him to work, the pay he gives depends upon the length of time the man works. His strength is only a measure of his ability to be of value. If he is very strong, he may be worth $1.00 per hour, or if he is not so strong, he may be worth only 50 cents per hour. His pay, however, will depend upon this rate and the number of hours he works. If he works two hoiu^ at $1.00 per hour, he will get $1.00 x 2, or $2.00, while he would get $5.00 if he should work five hours. Likewise, time must be taken into consideration in calcu- lating the value and cost of electrical power. The unit most commonly used is the kilowatt-hour, which, as the name indi- cates, is the expending of one kilowatt of power for one hour. 96. Measuring Kilowatt-Hours. — The number of kilo- watt-hours of power used in any circuit can be calculated by 90 PRACTICAL ELECTRICITY FOR BEGINNERS Fig. 57. Common kilo- watt-hour meter. This meter is usually placed near the entrance switch in house installations. multiplying the number of kilowatts being used by the num- ber of hours used; that is, if ten 100-watt lamps are used from 8 o'clock until 10 o'clock, the number of kilowatt-hours would be 10 X 100 X 2 divided by 1000, or 2. Such calculations are of little value ordinarily because lamps are turned on and off frequently and are used for only a few minutes at times and for hours at other times, so a meter has been devised which reads directly in kilowatt -hours (Fig. 57). These meters are used almost exclusively in the measur- ing of the power consumption in the home and in fac- tories and shops. 97. Beading the Eilowatt-Hour Meter.— It is impor- tant that every person using electrical power be able to read a kilowatt -hour meter because of the fact that power companies base their charges for power upon the readings taken from it. Thus, it is often desirable to be able to check the readings taken by the representative of the company. It will be seen by studying the register dials of a meter (Fig. 58), that the pomter at the extreme right, while making one revolution in a clock-wise direction, renters 10 kilowatt- FlG. 58. Showing the dials on a kilo- watt-hour meter, together with their direction of rotation. ELECTRICAL MEASUREMENTS 91 hours; that the one on the left of this, while making one revo- lution in a counter clock-wise direction, registers 100 kilo- watt-hours; that the third from the right, while making one revolution in a clock-wise direction, registers 1,000 kilowatt- hours, and that when one on the extreme left makes one revo- lution in a counter clock-wise direction. It registers 10,000 kilowatt-hours. While the first, the one on the extreme right, makes one complete revolution, the one next to it is passing from one number to the next and while that one is making a complete revolution, the one next to it is passing from one number to the next, etc. The 10 pointer will have to revolve 10 times while the 100 pointer is revolv- ing once, and the 100 pointer will have to make 10 complete revolutions before the 1,000 completes one revolution. A little study will show, then, that in reading the meter it is possible to start at the left and read the smaller numbers on the four dials (Fig. 59). This is a general rule to follow, but is quite likely to be found hard to apply in cases where one of the pointers is very nearly directly over a number. For ex- ample (Fig. 60), suppose the 10 pointer is just beyond the 9, the 100 pointer is almost directly over the 2, the 1,000 pointer is just past the 8, and the 10,000 pointer is nearly to the 2. The reading might be taken as 1,829 when it should be 1,819. Whenever a pointer is nearly directly over a number, it is 1401 Fig. 69. Method of reading a kilo- watt-hour meter by reading from left to right, taking the smaller number on each dial. 92 PRACTICAL ELECTRICITY FOR BEGINNERS best to start at the right and to read backward on the dials, then it is possible to tell what the pointer near the number should be read. To illustrate, take the example above. The reading on the 10 dial is 9, which indicates that when it has moved just a little far- ther, to the 0, the pointer on the 100 dial will be di- rectly over a number. In this case, the number is 2, but from, the location of the pointer on the first, just past the 9, it will be seen that the reading is still 1, even tho it appears to be 2. The same reason- ing should be applied if any of the other pointers are very near a number. 1819 Fig. 60. Method of reading a kilo- watt-hour meter when one of the point- ers is almost directly over a number. The reading in this case is taken from right to left. Summary of Principles in Chapter XI 1. Units are required in electrical applications to make possible definite measurements. 2. The most common electrical units are the volt, the ampere, the watt, the kilowatt, and the kilowatt-hour. 3. The volt is the unit of electrical pressure. 4. The ampere is the unit of rate of flow of electrical current. 6. The watt is the unit of electrical power. 6. The kilowatt-hour is the unit upon which power charges are based. Questions 1 . Why is it necessary to have electrical units? 2. What is meant by voltage and what are some common examples? 3. How is voltage measured? 4. What is meant by amperage and what are some common ex- amples? ELECTRICAL MEASUREMENTS 93 6. How is the total amperage in a circuit determined? 6. How are amperes measured? 7. What is meant by a watt? 8. What is a kilowatt? 9. How can watts be determined? 10. Why is it necessary to have such a unit as a kilowatt-hourT 11. How are kilowatt-hours measured ? 12. Describe the dial of a kilowatt-hour meter. 13. How do you read a kilowatt-hour meter? 14. How should a kilowatt-hour meter be read when one of the pointers is almost directly over a number? 15. What is the value of being able to read a meter? Suggestions 1. Note the ammeter on your automobile and see if you can read it. 2. Look at the name plate of every piece of heating apparatus you see and find out how many amperes it draws. 3. Look at the watt mark on the lamp in your basement and figure out how many kilowatt-hours of power would be wasted if you should leave it on all night. 4. Work out any of the problems involving power that you can think of or find in other books. 5. Make a careful study of the dial of a kilowatt-hour meter and make a drawing of it. 6. Make drawings of kilowatt-hour meter dials on small sheets of paper and place the pointers in different positions. Then, following the instructions given in this book, write down the correct readings. 7. Take the reading of the meter in your house on the day that the meter man does and see if your reading checks with his when you get your bill. 8. Observe all of the meters you have a chance to and see if you can tell what they are used for and what the readings are. CHAPTER XII Dangers Involved in Using Electricity; How to Avoid Them 98. Why Be Afraid of Electricity.— Since it is a well- known fact that electric shocks are sometimes dangerous, it is well to take up the manner in which it is possible to receive them and to show, also, how electricity can be handled with absolute safety. There seems to exist a natural fear of elec- tricity on the part of many and a feeling that they are liable to be electrocuted at any moment while they are using electrical apparatus. Of course, these are unfounded in most cases, but we all know there is the possibility of getting a shock if electrical apparatus is not handled properly. This is, how- ever, only a strong point in the proof that everybody should know something about electricity and its actions. Let us consider these points in a simple and ordinary man- ner with the hope that they may be made clear. Water, as we all know, is one of the necessities of life. It is used for drinking purposes; it is used for cleansing; we bathe in it; we go riding on it, and it is sprinkled on our gardens and lawns. Sometimes it is used for power purposes also. Yet, if one falls into too much of it and is unable to get out, he drowns. This does not mean, however, that whenever water is used, there is a possibihty of being drowned, and very few fear it. People know how to use water properly. The chief difference between the use of water and elec- tricity is that everybody is familiar with the former, but very few with the latter. A baby does not realize the danger of DANGERS IN USING ELECTRICITY 96 playing in water until he learns that he may drown if he falls in where it is too deep. More people have been drowned than have been electrocuted. There is absolutely no danger involved if electricity is used properly, but if the user is not familiar with its actions, he may bring about the possibility of a heavy current passing thru his body which might in ex- treme cases cause death. In the following discussions, an at- tempt will be made to show just wherein the dangers lie in making use of this wonderful power and to tell how to avoid them absolutely. 99. How It Is Possible to Get a Shock. — First, let us understand that before one can get a shock, he mast make possible the flowing of electrical current thru his body ; that is, the body, or part of it, must form a part of an electrical cir- cuit. This may be brought about by touching the terminals in an electrical outlet or the bare wires in an electrical system. Then, too, it is barely possible, in some cases explained later, for this to be brought about by touching an electrical termi- nal, or the frame of a piece of electrical apparatus, while in close contact with the ground or with some conducting mate- rial connected with it. The human body is not a very good conductor of electricity, however, and relatively high voltages are required to force current thru it. A person could hold onto the terminals of a storage battery or a dry cell indefinite- ly without feeling any effect whatsoever, but pressures as low as those afforded by these are not sufficiently high for heating and lighting, and batteries are too expensive, so we find gen- erator circuits most commonly used and the pressure is usually 110 volts, seventy-five times that of a dry cell. This pressure, altho not dangerous, is sufficient to force consider- 96 PRACTICAL ELECTRICITY FOR BEGINNERS able current thru the body if good contact is made with the conducting circuits. To cause very great harm, electricity must pass thru the entire body, which is ordinarily practically impossible except as in cases mentioned later. 100. How One Gets a Shock from a Lamp Socket. — If a person, while repairing a lamp socket, or tampering with it, while the current is on, touches the little piece in the base and, at the same time, the shell of brass on the inside, he will get a little shock which will simply cause him to jerk his hand away. Then, too, it is possible that he might get a slight shock by touching this little piece and the outside of the socket if one of the wires happened to be touching it acci- dentally. Neither of these shocks would be dangerous, and this is practically all that can happen in ordinary cases except possibly in the bath room, the kitchen, or in the basement of the house, and in these only as described later. It is possible, that in some cases, bared wires or loose connections may make slight shocks possible, but they are no more dangerous than those received from a socket or receptacle. It will be seen, then, that there is very little chance for any- thing more than a light shock in the ordinary use of elec- trical devices. 101. Slight Shocks Are Harmless. — ^Many of the com- paratively few accidents occurring in the home are due to fright rather than to the electric shock. Many persons are scared by a little tinge of electricity which probably does them more good than harm. Some people nearly go wild when they scarcely feel electrical current, and many of them imagine they have received an electric shock when they have received nothing of the sort. This excitement is due largely DANGERS IN USING ELECTRICITY 97 to the fear of electricity. The writer has tested hundreds of lighting and heating circuits for current by touching the terminals with the thumb and forefinger of the right hand, and has never felt any evil effects. In fact, the feeling is a rather pleasant one. He does not do this, however, imless he is absolutely sure that he is not in contact with any conduct- ing material running to the ground and that he is not standing on a damp basement floor. This is mentioned only for the purpose of showing that there is very little danger involved in handling or repairing heating and lighting circuits in the home. If you receive a shock wlule doing some work, simply forget it and open the switch, the main one preferably, and examine the apparatus you are using for bare wires, loose con- nections or for a place where the wire has come in contact with the frame. 102. Where the Real Danger Exists. — In the larger villages and cities where power is furnished by a power com- pany or where it is transmitted from some distant generating plant, it is usually carried under a very high pressure which is reduced before it is distributed. Then, too, there are usually electric street-car lines which operate on high voltages. In such cases, it is sometimes possible to receive a shock, if con- ditions happen to be just right, if one attempts to turn on a lamp while standing in a bath tub, while leaning against a gas stove or a sink, while standing on a damp basement floor, or while in close contact with any conducting material running to the ground. Any possibility of this happening can be avoided by taking proper precautions, which will probably be made clear in the following discussion: The ground, especially when it is damp, will carry elec- 98 PRACTICAL ELECTRICITY FOR BEGINNERS tricity if the pressure is great enough. In cities where there are gas or water pipes under the ground, these form a good conducting circuit for electricity. One of the wires of an electric circuit may be connected to the ground thru a pipe, or in any other manner, without affecting the flow of cur- rent. The fact is that, for reasons unexplainable here, in a great many cases a connection is made purposely between one side of a line and the ground. The groimd, then, may be in contact with one side of several different circuits, which may have exceedingly high or exceedingly low pressures on them, or with both kinds without causing harm. This may seem strange to some, but consider the street-car lines. The rails, which are placed upon the ground, are one of the conducting sides of the circuit just as one of the wires running to a lamp is one. The other side is the wire upon which the trolley nms. Every time one steps upon the rail then, he comes in contact with one side of a high-voltage line. No current will flow, however, unless a connection is made be- tween the rails and the wire. If, now, a wire were accident- ally touching the trolley wire and it should be touched by one standing on the groimd, the current might pass from the rail thru the ground to the person's feet, thru his body to the wire, and thru the wire to the trolley wire, and he might receive a severe shock. This would depend upon the completeness of the connections and the dampness of the ground. There is, nevertheless, a possibility that the person might receive a fatal shock in this manner. In a house we often have an arrangement somewhat similar to the street-car line in many respects, altho it does not have the same appearance. Two wires run into it, one of which DANGERS IN USING ELECTRICITY 99 has probably been connected to the ground at some distant point. If this be true, the wire so connected may be consid- ered the rails and the other the trolley wire. There is a pos- sibility that this second wire is in contact with some high- voltage line outside of the house; perhaps touching a trolley or other high-voltage wire. It will be seen, then, that if such should be the case, a person in close contact with the ground, or a conducting material running to it, might receive a fatal shock if he should take hold of, or come in contact with, any piece of electrical apparatxis which happened to be coimected, by accident, to the ungrounded wire. It is in this manner that practically every fatal accident has been brought about in the home or shop. 103. Examples of Accidents. — The following cases are known by the author to have happened and are given only to show how they were brought about and how they might have been avoided : A girl was taking a bath one evening when someone called her. She had forgotten whether or not she had locked the door and reached to turn on a light so she might see. As she touched the lamp socket, she received a fatal shock. This would not have happened if she had been out of the bath tub. But she was probably in contact with the pipe connected with the tub and the wire inside of the socket was probably loose and in contact with the outside shell. In another case, the fuses were blown dining the evening, leaAnng the house in darkness, and the man of the house went into the basement in the dark and felt around with his hand to find the fuses and to put new ones in. As his hand came in contact with the main terminals, he was electrocuted. This 100 PRACTICAL ELECTRICITY FOR BEGINNERS could have been avoided if he had taken a light of some kind and had stood on a chair or something which would com- pletely insulate him from the ground. In another case, which happened in a shop, a man caught his toe and fell just as he was about to close a switch of the open type. His hand accidentally came in contact with the hne terminals and he reached for a water pipe to keep himself from falling. When his hand came in contact with the water pipe, he was electrocuted. This would not have happened had he kept away from the pipe. These three accidents are about the only ones occiirring in this part of the country in the past five years and are, of course, extreme cases. Even these few possibilities for acci- dent are being done away with as rapidly as possible by making use of enclosed switches, by connecting switch boxes and motor frames to the ground, and by various other meth- ods of safety, so that at the present time there is very, very little danger involved. It is well, however, to know that in some few cases, accidents are possible and to take particular pains to avoid any chance of bringing them about. Summary op Principles in Chapter XII 1. It is impossible to receive a shock unless the body is made part of an electrical circuit. 2. Slight electrical shocks are harmless. 3. Severe shocks are impossible except in extreme cases where one is standing on a damp basement floor, or in contact with a water or gas pipe. Questions 1. Is electricity as ordinarily employed in the home dangerous? 2. How is it possible to get a shock from a lamp socket? DANGERS IN USING ELECTRICITY 101 3. In what other manner might one get a shock? 4 . Are slight electrical shocks h armful ? 5. Where does the real danger exist in a home? 6. Are accidents in homes very common? 7. Tell in your own words how an accident might occur. 8. Describe any accident you may have heard of and see if you can explain how it might have been avoided. Suggestions 1. Always be careful when you turn on a lamp in a bath-room, kitchen or basement. 2. Before you attempt to repair a part of an electrical circuit, especially in any of these places, open the main switch. 3. When you replace fuses in a branch circuit open the main switch if possible. 4. If it is ever necessary to replace the main fuses in a basement be sure that you are insulated from the ground and that you use only one hand. 102 PRACTICAL ELECTRICITY FOR BEGINNERS INDEX Page A Accidents, examples of 99 Ampere, definition of 85 Amperes, measurement of 86 Applications of electricity 10 Attachment troubles in heaters . 63 B Base, lamp 69 Battery lamps 40 Battery-lamp marks 40 Battery lamps on too high volt- age 40 Battery lamps on too low volt- age 41 Battery lighting 39 Battery, voltage of a 42 Bell circuits 32 Bell circuits, break in 36 Bell circuits, connecting of .... 34 Bell circuits, repairing 35 Bell circuit, short in a 36 Blown fuse, detecting a 76 Break in a bell circuit 36 Burnt-out heating element .... 65 Burnt-out lamp 74 Care of storage batteries 23 Cell, dry 20 Circuit 28 Circuits, bell 32 Circuits, heater 59 Circuit, lighting 72 Circuits, troubles in lighting. . .73 Conductors 12 Conducting materials 14 Conducting powers, table of . . . 17 Page Connecting bell circuits 34 Connecting, important points regarding 35 Connections, series 43 Connections, parallel 43 Connections made by extension cord 61 Cord, extension 59 Coverings, insulating 14 Coverings, rubber 15 Current, effects of 47 Current, heating effect of 47 Current, ho wit gets into a lamp. 69 Currents, transmission of 11 Description of a storage battery .22 Determining the voltage of a battery 42 Devices for heating 50 Dimming lamps 44 Dry cell 20 Dry cell operation 21 Dry cell uses 21 E Effects of current 47 Electricity, flow of 28 Electricity, importance of 10 Electricity, nature of 9 Electricity, dangers in use of . . .97 Electricity, why be afraid of ... 94 Electric lamps 67 Electrical currents 11 Electrical pressure 19 Element, burnt-out 65 Element, heating 50 Entrance switch 66 INDEX 103 Page Extension cord 60 Extension cord, connections made by 61 F Faults in fixtures 77 Filaments 68 Flatiron 51 Flow of electricity 28 Flow thru small wire 29 Flow thru large wire 29 Flow thru short wire 31 Flow thru long wire 31 Flow thru iron wire 30 Fuses 54 Fuses, description of 54 Fuses, detecting blown 62 Fuses in a house 55 Fuses, purpose of 53 Fuses, replacing of 57 Fuses, testing 54 G Gas-filled lamps 70 Generators 25 H Heat, generation of 48 Heat regulation 49 Heater circuits 59 Heater cord 59 Heater troubles 61 Heater-terminal defects 63 Heating devices 50 Heating effect of current 47 Heating elements 50 Heating element, burnt-out ... 65 Heating, principles of 50 Hydrometer 25 Hydrometer readings 25 Page I Importance of electricity 10 Insulating coverings 14 Insulators 16 J Joints 35 L Lamps, battery 40 Lamps 67 Lamp base 69 Lamp, burnt-out 74 Lamps, dimming of 44 Lamp filament 68 Lamps, gas-filled 70 Lamp, how current gets into. . .69 Lamp operation, importance of . 72 Lamp socket 74 Lamps, wattage mark on 70 Lamp, why it gives off light. . . .68 Lighting circuit 72 Lighting-circuit troubles 73 M Marks on battery lamps 40 Measuring amperes 86 Measuring kilowatts 88 Measuring kilowatt-hours 89 Measuring volts 84 Measuring watts 88 Metallic filaments 70 Meter, reading kilowatt-hour . . 90 Meter, kilowatt-hour 90 N Nature of electricity 9 Numbers on fuses 86 104 PRACTICAL ELECTRICITY FOR BEGINNERS Page o Operation of dry cells 21 Operation of storage batteries. 23 One-wire system 43 Parallel connections 43 Plug, extension cord 60 Plug troubles 62 Porcelain 16 Pressure, electrical 19 Pressure, supplying 20 Principles of heaters 50 Purpose of fuses 53 Push-buttons 34 Readings, hydrometer 24 Reading kilowatt-hour meter . . 90 Receptacle 60 Regulation of heat 49 Repairing bell circuits 36 Replacing fuses 67 Resistance 31 Rubber coverings 16 S Series connections 43 Shocks, dangerous 97 Shock from lamp socket 96 Shocks, how possible to get ... 95 Short circuits 78 Short circuits, tests for 79 Short in a bell circuit 36 Socket, lamp 74 Socket, poor connections in a. .76 Specific gravity 24 Page Storage battery 22 Storage battery operation 23 Storage battery, run-down ... .24 Storage battery uses 23 Switch, entrance 66 Switch, trouble in 74 Switch, wall 74 Taking hydrometer readings. . . 24 Test for short in bell circuit. . . .36 Test for break in bell circuit 37 Tests for short circuits 79 Testing fuses 64 Transmission of currents 11 Troubles in bell circuits 35 Troubles in heater circuits .... 61 Troubles in plugs 62 Troubles in lighting circuits ... 73 Units, common electrical 83 Units, necessity of 82 Uses of dry cells 21 Uses of storage batteries 23 Volts 83 Volts, measurement of 84 W Wall receptacle 60 Wall switch 74 Watts, definition of 87 Wattage marks on lamps 70 Watts, measurement of 88