f Current Fundamental Electricity Part II Electrical Heating AppliaU' Part III Salesmanship, Advertising and Store Management QUADiy MARK EDKON ELECTRIC APPLIANCE COMPANY, CHICAGO EDI SON SCHOOL OF THE UNIVERSITY OF ILLINOIS LIBRARY t'trst Assignment EDISON SCHOOL o/SALESMANSHIP Part I ELECTRICITY Lesson I Some Fundamentals OF Electricity EDISON electric APPLIANCE COMPANY, Inc. CHICAGO Copyright 1921 Edison Electric Appliance Company, Inc. r in ley FUNDAMENTALS OF ELECTRICITY JUST A FEW KEYS But They Open to Big Opportunities Before we start on this interesting and profit- able course let us have a brief, informal talk for the purpose of getting clearly in mind just what the careful study of these lessons is going to mean to you. We assume you are a salesman or would like to become one. You have chosen that work of your own accord and we take it for granted that you are interested in making it pay you as large a return in money as possible. You probably know many men who are sales- men in different lines. Some are more efficient than others; some are making more money than others. Generally speaking, the difference in classes of salesmen lies in the measure of their knowledge regarding the thing which they are selling. Some men can sell anything fairly well. Let us take such a man for an example. Say he is selling electrical appliances. He will be a better 4 or/"* ' r ‘ilO .’- 'acoJ EDISON SCHOOL OF SALESMANSHIP salesman — make more money — if he knows thor- oughly his line of appliances; their favorable points, their distinct advantages over other appli- ances. He will be a much better salesman if he has a thorough grasp of the underlying principles of salesmanship and of advertising (which is a direct branch of sales effort), plus a working knowledge of electricity. Putting it in a few words; The rewards of life go to men who KNOW! You will not find this course of training in salesmanship to be difficult. Electricity is an interesting subject. The principles of salesman- ship and of advertising are based largely on human nature, and human nature is always interesting. The only thing we ask is that you go through withthe course. There are only eighteen lessons and the time required each week is, at most, only a few hours of your spare time. Once started on the course, enthusiastically and with determination to finish it, we feel sure you will enjoy the lessons as much as any time you spend in reading. The facts and principles and rules that you master in this course will enable you to increase your selling ability and to increase your success in life. FUNDAMENTALS OF ELECTRICITY T to get the most XTL\^ V V from this course Look for the main points — the laws, the principles, the rules of the things studied. These primary rules are rela- tively few, and it will not be difficult for you to understand them and to store them in your memory for use when needed. The man who knows how to apply the principles has mas- tered the subject. SOME FUNDAMENTALS OF ELECTRICITY What Is Electricity? Have you ever considered the tremendous work which electricity is doing in the world today ? Electrical energy drives our machinery, lights our houses and buildings, transmits messages from one part of the world to the other. It makes possible the automobile, the street car, the sub- way and elevated trains. While we are able to recognize it by its properties, to measure it, and to harness it to do our work, what electricity really is, is not defi- nitely known. There have been many theories advanced. The greater part of these have been discarded. But a consideration of one or two of these theories will be helpful. For example, one theory held that electricity s EDISON SCHOOL OF SALESMANSHIP was a fluid which pervaded all matter. While this theory has been discarded it helps us to picture the nature of electricity. The latest theory holds that “electricity is a rapid vibration of the molecules of the conductor and in the space immediately surrounding the conductor.” A molecule is one of the tiny par- ticles of which all matter is composed, and is the smallest particle of matter which can exist by itself. The exact nature of these vibrations has not, as yet, been determined. It is assumed, however, that these electrical vibrations are similar to light and heat, and travel at the same speed as light; i.e., 186,000 miles per second. In this course we will concern ourselves especially with the properties of electricity, a knowledge of which has made its commercial application a reality, and we will see how these properties are applied in practice. Electricity Exists in Two Eorms — Static and Current Static Electricity As early as the year 600 B. C., it was known that the rubbing of certain substances together, as two pieces of amber for example, would make them attract light particles of matter. It was also discovered from time to time that other sub- stances, including rubber and glass, possessed this property of attraction when they were rubbed together. The early Greeks knew amber by the 6 FUNDAMENTALS OF ELECTRICITY name of “electron” and it is from this term that the word electricity was derived. What is produced by rubbing two pieces of amber, or rubber, or glass, etc., together is a form of energy that is known to us as static electricity or electricity at rest; i.e., under restraint but ready to discharge itself when released. Static electricity is produced by friction. The discharge of static electricity is noticeable in two familiar ways. One, in the crackling of the hair when combed in very dry weather, and the other, the crackling spark produced when an object is touched after one has shuffled one’s feet across a carpet. Furthermore, lightning is the discharge of static electricity which has been stored up in the clouds. Static electricity, which is one form of elec- trical energy, does not enter into the operation of electrical appliances commonly used in the home. These operate by current electricity, which is another form. There Are Two Kinds of Static Electrical Charges— Positive and Negative Let us return again for a moment to the sub- ject of static electricity, which, we have found, is produced by friction, by rubbing two substances together. Static electricity is either positive or negative. Two objects which are charged with positive electricity or two objects which are charged with negative electricity have a tend- ency to repel one another. Objects which are 7 EDISON SCHOOL OF SALESMANSHIP oppositely charged attract one another. We find that if we take a piece of glass and rub it with a piece of silk, the glass will have z. positive charge. If, on the other hand, a piece of sealing wax is rubbed with flannel, the sealing wax has a negative charge. This is because of the nature of the various substances with which we have to deal; i.e., their inherent qualities. Current Electricity The second form of electricity is current elec- tricity., or electricity in motion. Current electricity never exists in stationary form. It exists only when in motion. As it is current electricity which is used in electrical appliances in the home, we will confine ourselves in this course to a consideration and discussion of this form only. What Is Meant by a Circuit The path along and in which electricity flows is known as a circuit. In flowing over this path or circuit the current electricity naturally follows a certain direction, which direction is, of course, always out from the point of highest pressure. In any device generating current electricity, there are always two poles, as hereinafter shown, which are known as the positive and negative poles. The student should note that this has nothing to do with the positive and negative charges which we have seen to exist in static electricity. In current electricity, positive and 8 FUNDAMENTALS OF ELECTRICITY negative current refer only to the direction of flow from or to the source of supply. The pole from which the current flows out is known as the positive pole, or the pole of high pressure. The negative pole isthepole through which thecurrent returns to the source of supply and is the pole of low pressure. A circuit may now be more fully defined as that path over which the electric cur- rent flows from its starting pointy or positive pole, out over its path and again back to its source, or negative pole. Current Electricity — How Produced Current electricity is ordinarily produced in two ways; by chemical action and by magnetism. The most common example of current elec- tricity produced by chemical action occurs in the well known electric battery used in operation of electric door bells, telephones, telegraphs and 9 EDISON SCHOOL OF SALESMANSHIP Other similar devices. These are known as “primary” batteries to distinguish them from the “secondary” or “storage” batteries. A primary battery is a device for converting chemical energy directly into electrical energy. There are two kinds of primary batteries, known as “wet” and “dry.” The ordinary “wet” battery consists of two pieces or poles of different metals (poles gen- erally of copper and zinc) placed in a liquid which acts in different ways on these metals. The liquid used is generally diluted sulphuric acid or a solution of sal-ammoniac. When the metals are connected by a wire outside the liquid, electric energy is generated by the chemical action of the acidon themetals and then flows through the wire. The chemical action which takes place in this conversion of chemical energy into electrical energy is simple. The sulphuric acid attacks the zinc plate, causing it to gradually waste away. Just as a heated body will give off its heat to one of lower temperature, so also the zinc plate in this process of consumption caused by the attack upon it of the sulphuric acid gives off the elec- trical energy, which is produced, to the copper plate. The copper plate is therefore, as will readily be seen, continually being charged with electrical energy by the action of the solution. The copper plate or pole being of higher potential or pressure than the zinc plate or pole, continu- ally discharges electric current, which, as has been explained, flows out over the circuit to the point 10 FUNDAMENTALS OF ELECTRICITY of lower pressure, which in this case is represented by the zinc or negative pole. Thus are established two distinct parts of the path for the electric current. The first, from the zinc through the solution to the copper; the second, from the copper through the outside wire, back to the zinc. This, then, is a simple example of what an electric circuit is. Anything to be aflFected by the current generated in the battery, must be so connected on the outside wire before mentioned that the current may pass in at one side, out at the other and back to its point of origin. A dry battery is practically the same, except- ing that the solution exists in a dry paste form. The second method of producing current elec- tricity isbymagnetism. This is commercially done by means of the so-called dynamo. The curren t used in the home and in the commercial world is princi- pally produced by magnetism through dynamos. There are two kinds of dynamos: those which produce direct current and those which produce alternating current. By - direct current we mean that current which flows continually in one direction; that is, it starts from one pole (the “positive pole”) and flows continually through the circuit to the other pole (the “negative pole”). By alternat- ing current we mean current Showing how a circuit - •I’ll 1 * formed on an ordinary which periodically changes its push-bumn beii outfit direction, flowing first in one direction completely 11 EDISON SCHOOL OF SALESMANSHIP through the circuit, and then in the opposite direction completely through the circuit; the poles change from positive and negative to negative and positive, alternating back and forth, and thus reversing the current. Direct current is necessary for certain pur- poses, while alternating current is necessary or desirable for others, and is the current most generally used. For example, in electroplating di- rect current only can be used; i.e., current which flows constantly in one direction. For lighting purposes, on the other hand, alternating current is generally advisable, although direct is often used. This will be explained in a subsequent lesson. Referring to our definition of alternating current you will note that it is current which continually reverses its direction, flowing first forward and then backward, etc. One such complete reversal of the current, forward and back- ward, is known as a cycle. In some dynamos producing alternating current the current makes 60 complete reversals or cycles each second, or makes 1 20 alternations per second. This is known as a 60-cycle dynamo. The number of complete cycles which the current makes each second is known as the frequency of the current. While there are dynamos which produce current of other frequencies, those used for producing electric light in this country generally have a fre- quency of 60 cycles. The principal diflFerence between an alternat- ing current and direct current dynamo lies in the 12 FUNDAMENTALS OF ELECTRICITY fact that a direct current dynamo has what is called a commutator; because, as a matter of fact, both kinds of machines generate alternating current. The commutator on a direct current machine is a device by which the current is col- lected and sent out continuously in one direction. The commutator is a cylinder on the shaft of the direct current generator, composed usually of copper segments separated from each other by electrical insulation, revolving under collector brushes placed at certain points. These brushes are usually made of carbon and correspond to the positive and negative poles of a battery. Alternating current generators do not have commutators. Conduction In theory, all bodies conduct electricity to a greater or lesser extent. It follows, therefore, stating the matter the other way, that all bodies resist the passage of electricity to a lesser or greater extent. Substances which allow electricity to pass through them readily are known as conduc- tors. Those which materially resist the passage of electricity are known as non-conductors or insulators, as hereinafter described. Metals are the best conductors and are never classed as non-conductors or insulators. In order to give you an idea as to the relative resistance of different metals, we will tabulate a few. In this table, silver for a given size or shape (not weight) is shown as having the least resistance and, there- fore, is the best conductor. For the purpose of 13 EDISON SCHOOL OF SALESMANSHIP comparison we have taken silver as “1.” By referring to this table, you will see that mercury, though a metal, has over 62 times the resistance of silver; or, silver has more than 62 times the conductivity of mercury: Silver ... 1.000 Iron ... 6.460 Copper ... 1.086 Nickel ... 7.628 Gold ... 1.393 Tin ... 8.091 Aluminum ... 1.935 Lead ... 13.050 Zinc ... 3.741 Antimony ... ... 21.645 Platinum ... 6.022 Mercury ... 62.730 For commercial purposes copper is generally used, as it is almost as good a conductor as silver and is much lower in cost, and its great ductility permits it to be drawn out into wire. Insulation and Insulators As above implied, an insulator is the opposite of a conductor, being asubstancewhich resists the passage of electricity. It is not possible, however, to draw a sharp distinction between conductors and insulators, as most substances conduct a little, and even good conductors vary greatly in their conductivity or in the resistance which they offer to the passage of current electricity. The following are considered among the best insulators: Dry Air Mica Glass India Rubber Porcelain Silk Paraffin Dry Wood Vulcanite Various Oils Shellac Chemically Pure Water 14 FUNDAMENTALS OF ELECTRICITY It is to be noted that ordinary water, being more or less impure, is a conductor of electricity. Electric light, telephone and telegraph wires are supported on glass or porcelain insulators to prevent leakage of the current. The choice of the insulator to use in each instance is, of course, always governed by the conditions which are to be met. For example, oil is an excellent insulator where it is desired to insulate moving parts which can be immersed in the insulating material itself. It would obviously be impossible, however, to use it for insulating wire suspended on poles. Paraffin is principally used to permeate porous insulating materials, such as cotton, silk and the like, to assist in preventing leakage of current. As an example of a substance which is of par- ticular usefulness as an insulator we mention mica. Besides being a good electrical insulating material, mica is capable of withstanding high temperature. Hence, it is widely used in elec- trically heated appliances for insulating the heat- ing element from the balance of the appliance. In addition to its ability to withstand high temperature, thin sheet mica is a comparatively good conductor of heat, so that the heat generated, when used as above, easily passes from the heating element to that place in the appliance where it is to be utilized. 15 PROBLEMS Part I ELECTRICITY LESSON II NAME STUDENT NUMBER STREET AND MUMBER OR P. O. ADDRESS CITY STATE EDISON ELECTRIC APPLIANCE COMPANY, Inc. CHICAGO ' fo un) •XjpiJloap 9jnsB3iu ijoiifAV Xq squn piuauiepunj aajqa aqj SNOixsaaO THE PROBLEMS The most important part of your training in. this Course is your work on the Problems. When you work the problems, you concentrate on the most important points of each lesson, and you get these points clear in your own mind. Work your problems on this Sheet, writing the answer in the blank space under each question. Sign your name, address, business connection, and the date, and mail the Problem Sheet to us. We wijl go over your answers, correct them, give your paper a grading, and return to you. Upon your satisfactory completion of the course, you will be awarded a certificate. Address your replies to EDISON SCHOOL 0/ SALESMANSHIP Care oj EDISON ELECTRIC APPLIANCE COMPANY, Inc. 5660 Taylor Street, Chicago PROBLEMS Part I ELECTRICITY LESSON II EDISON ELECTRIC APPLIANCE COMPANY, Inc. CHICAGO 3. What is the unit of energy? How is it found ? 4. How much current flows when 220 volts overcomes a resistance of 20 ohms ? 5. Define Watt; Kilowatt; KWH. 6, How is the wattage of any electrical appliance found? 7. If an appliance designed for and used on a 110-volt circuit is stamped SOO watts, how many amperes would it use ? 8. If you connect an appliance, designed to operate at 100 volts, on a 200-volt circuit, what will happen and why? (Make answers brief and concise; if additional room is needed use space below, making proper reference to question number.) The man who puts his knowledge to the test will always get farther in life than those who are not sure as to just what they know THE PROBLEMS The most important part of your training in. this [bourse is your work on the Problems. When you work the problems, you concentrate on :he most important points of each lesson, and you get :hese points clear in your own mind. Work your problems on this Sheet, writing the answer in the blank space under each question. Sign your name, address, business connection, and the date, and mail the Problem Sheet to us. We will go over your answers, correct them, give y^our paper a grading, and return to you. Upon your satisfactory completion of the course, y^ou will be awarded a certificate. Address your replies to EDISON SCHOOL of SALESMANSHIP Care of EDISON ELECTRIC APPLIANCE COMPANY, Inc. 5660 Taylor Street, Chicago Edison School of Salesmanship 5600 WEST TAYLOR STREET CHICAGO, ILL. ANSWERS TO QUESTIONS Assignment 2 - Part 1. 1. Current strength (The Ampere); Resistance (The Ohm); Pressure, Electromotive force, (The Volt). See Pages 3 to 8 2. Th e Amper e is the amount of current flowing along a wire when there is one unit of pressure overcom- ing one unit of resistance. It is that unit by which we measure the strength of the current, or the rate of flow. The Ohm is the amount of resistance that allows a current strength of one ampere to flow when there is a pressure of one volt. The Volt is that force v/hich will cause a current strength of one ampere to flow through a resistance of one Ohm. See Pages 3 to 9 3. The unit of Electric power, or rate of using energy, is the Watt. Multiply the volts by amperes. W - V X A. 4. Using the formula on Page 1 0 A = ^ and substituting in this formula the two values which we know in order to find the third one which we do not know, we get: 220 j j See Page 10 5. A Watt is that unit of power produced when one ampere flows in a circuit under a pressure of one volt. The Kilowatt is one thousand watts (Kilo - 1000). KWH is the abbreviation of Kilowatt-Hour and repre- sents a thousand watts for one hour. See Pages 11-16 6. Multiply the volts by the amperes found on name-plate to get the wattage of an appliance. See Page 1 8 7. Amperes equal watts divided by volts, or A = Substituting in the formula, we get: Amperes = = 4.54 See Page 1 8 8. If we connect a 100 volt appliance on a 200 volt circuit, the appliance will probably burnout because we get four times the power or wattage. By doubling the voltage we double the current and since the watt- age is the product of the two, we get four times the wattage. See Page 19 Second Assignment EDISON SCHOOL o/SALESMANSHIP Part I ELECTRICITY L,esson II UNITS OF MEASUREMENT EDISON ELECTRIC APPLIANCE COMPANY, Inc. CHICAGO Copyright 1921 Edison Electric Appliance Company, Inc. EDISON SCHOOL of SALESMANSHIP Part I ELECTRICITY Lesson II Units of Measurement I N the last lesson we learned of the nature and of certain properties of electricity. In this lesson we will deal with the way elec- tricity is measured. It seems strange that we do not know what electricity really is, and yet we can measure it very accurately. In order to get a fairly clear idea as to how electricity is measured, let us liken the flow of electricity to the flow of water. Suppose that you had a big reservoir of water up in the mountains, and were studying ways to bring that water down into the valley in order to irrigate your farm. The Unit of Current Strength — The Ampere One of the first things you would have to decide would be how large a flow you needed. Whether you would want much water or only a small quantity to be flowing. 3 EDISON SCHOOL OF SALESMANSHIP If you wanted much water, you would dig a large ditch to carry it. If you wanted only a little water, you would dig a small ditch. In other words, one of the things you would have to decide would be the rate of flow of the water. Now, just as there can be a certain rate of flow of water in a ditch, so there can be a definite rate of flow of electric cu7-rent along a wire. The RATE OF FLOW of the current, also known as the strength of the current, can be measured. The unit of measurement is called the ampere. Just as, with a current of water, you can say that there are so many gallons per minute com- ing through, so with electricity you can say that there are so many amperes coming through. To give you some idea of the amount of current an ampere represents: The ordinary 25-watt incandescent Mazda lamp (on the usual 110 volt circuit) has a current flowing through it of about of an ampere; a 50-watt Mazda lamp, about of an ampere. What Makes Current Strength — Pressure Divided by Resistance But you readily see, do you not, that the strength of any current depends on two other factors — the amount of pressure behind the cur- 4 UNITS O F MEASUREMENT rent driving it forward, and the amount of resistance in the path of the current, trying to stop it. Let us give an illustration: Suppose you have a cur- rent of water flowing through an inch pipe. Then suppose you All that pipe with buck- shot. What happens? Why, the current slows up. Just as in our previous illustra- tion if we had fllled the ditch with stones. The buckshot is a resistance. In effect, it reduces the size of the pipe. The greater you make the resistance, the less current you get. But now suppose that you put a force pump on that pipe in order to bring force or pressure on that current of water. What y; happens? The current increases. The greater the pressure, or force, the greater the strength of your current. The man at the force pump can INCREASE the strength of the cur- rent of water by in- creasing the pressure The man at the nozzle can DECREASE the strength of the current of water by increasing the resistance (turn- ing the stop-cock) The strength of the current coming from the nozzle is the result of the pressure divided by the resistance The same formula holds for electric currents 5 EDISON SCHOOI. OF SALESMANSHIP Let US illustrate this with a little arithmetic: Suppose you had a current of water flowing through a trough at the rate of 100 gallons a minute. If you double the pressure or force behind that water, you will get 2 times 100 or 200 gallons a minute. But then if you should double the resistance of those 200 gallons, you would cut the current in two. You would have one-half of 200 gallons, or 100 gallons. So here is the formula that you should fasten in your memory: The strength of the current equals the pressure divided by the resistance. (This is known as Ohm’s law). Electric Resistance We have learned in the first lesson that sub- stances differ in the readiness with which they will permit electric current to be conducted along them, and we have classified them as good or poor conductors according to their ability to conduct current. The opposition which a con- ductor offers, tending to retard or restrict the flow of the electric current, is called the resistance. Resistance Depends Upon Various Factors The resistance which a conductor (of uniform shape) offers depends primarily upon length and 6 UNITS O F M E A S U R E M E N T the area of its cross section; in the case of round or square conductors, therefore, upon length and the square of their diameter. (You learned in arithmetic that the areas of squares and circles vary as the square of their diameters.) For example, a conductor twenty feet in length will offer twice as much resistance to an electric current as a conductor ten feet long, all other things being equal. Similarly the greater the diameter of the wire, the less resistance it offers, just as a large waterpipe offers less resistance to the flow of water than a small pipe. Although by illustration we have compared electricity to water, electricity of course, is not a liquid and does not “flow” like water. But the analogy is helpful to the student. We have pointed out that the resistance offered is directly proportional to the length. Now then, the amount of resistance is also inversely pro- portional to the square of the diameter of the conductor. For example: No. 24 wire has a diameter of .02 inch. No. 30 wire has a diameter of .01 inch or one half of the diameter of No. 24 wire. It takes 39 feet of No. 24 copper wire to give a resistance of one unit, but it takes only 9.7 feet of No. 30 wire, or one fourth as much, to offer the same amount of resistance. In other words by halving the diameter of a wire we increase the resistance four times. So we 7 EDISON SCHOOL OF SALESMANSHIP see that the larger the wire, the less resistance it offers to the current. The amount of resistance offered by a wire depends also upon the material of which it is made. For example; only 2.2 feet of No. 24 nickel-silver wire will offer a resistance of one unit, whereas it takes 39 feet of No. 24 copper wire to give the same resistance. Copper is the best commercial conductor; hence, wires for carrying electric current are almost universally made of copper. Temperature (of the conductor) also is a factor in the resistance offered. Of this we will speak in a later lesson. The Unit of Resistance— The Ohm The unit of resistance is called an ohm, and one ohm may be defined as the amount of resist- ance that allows a current strength of one ampere to flow when there is a pressure of one volt. (The resistance of a copper wire one and one-fifth inch long and one-thousandth of an inch in diameter, is about one ohm. The resistance of 528 feet of iron wire one-third of an inch in diameter is also about one ohm.) In many instances resistance is an undesir- able factor as it retards electric current and uses up power; but we shall see as we progress that it is largely because of resistance that we can 8 UNITS OF MEASUREMENT develop the heat which is the necessary factor in all electrical heating appliances. We merely call this point to your attention here and will treat of it more fully in a later lesson. The Unit of Electrical Pressure— The Volt The driving force which produces a flow of electricity is known as the electromotive force. It is electrical pressure, just as we speak of water pressure. The unit of electromotive force, or pressure, is known as a volt. The volt accord- ingly may be considered as the unit by which electrical pressure is measured. It is defined as that force which will cause a current strength of one ampere to flow through a resistance of one ohm. So that you may obtain an idea of about how much electric pressure a volt is, we might mention that the electric pressure in the ordinary dry battery runs from 1.1 to 1.5 volts and that the usual lighting circuit in this country operates at 110 volts. In many foreign coun- tries the lighting circuit operates at 220 volts. There Is a Definite Relation Between the Units of Measurement You remember the formula that we gave a few paragraphs back — “The strength of the current equals the pressure divided by the resis- tance.” 9 EDISON SCHOOL OF SALESMANSHIP Now let US express this in electrical terms, as follows : Amperes Equal the Volts Divided By the Ohms Or, if we let “A” stand for amperes, “V” for volts, and “O” for ohms, we may express this relation bv the following equation: a!y o or, if we say, A = 4, V = 160, and O = 40, then we have— 160 (volts) 4 (amperes) = ^ ^ 40 (ohms) But if 4= then it is also true that 4 x 40=160. 40 Using the same arithmetical rule with our letters, we can sav that if A = — then A x O = V, HO V ' o and U= ^ • A As a practical illustration take the standard 6 -pound Hot Point or 6 -pound Edison electric flatiron, 110 volts: Amperes (volts) ^ ^ 25 (approx.) 21.1 (ohms) From these equations you will see that if two of the three units are known, the third is easily found by substituting the figures known in the equation and then solving for the un- known quantity. For example, let us assume that we have a pressure of 150 volts and a resistance of 30 ohms 10 UNITS O F MEASURE M ENT The The The The Ampere Volt Ohm Watt : 'll.. Measuring the Electric Current The four units of measurement and desire to find the current which is flowing in amperes. Substituting the known quantities in the equation we find that A= or A=5. 30 In other words, there are 5 amperes of current flowing. Again, let us assume that we have a current strength of 7 amperes and a resistance of 20 ohms, and we wish to find the amount of pres- sure in volts. Applying our formula again we find that ^ V= 7x20 or V= 140 In other words the electrical pressure is 140 volts. And so in every instance where two units are known, the third is easily found. The Unit of Power— The Watt We have now considered the measurement of electrical flow, pressure and resistance, which 11 EDISON SCHOOL OF SALESMANSHIP we have learned are measured by units known as the ampere, the volt, and the ohm, respective- ly. There is another factor the measurement of which is highly important — power, or rate of doing work. The unit of measurement of electrical ■power is known as the watt, just as the unit of mechanical power is the horsepower; 746 watts is equivalent to one horsepower. Let us get clearly in mind this question of rate of doing work, or activity, or power, of which a watt is the measure. Rate of work is found by dividing the work done by the time consumed in the process. The expression “Sixty miles per hour” ex- presses a rate of speed; you do not know how far the train will go or how long it will take — you only have the rate. It takes an engine of a certain power to pull a certain length of train at that rate of speed. The power represents the rate of doing work; the actual amount of energy expended or work done in making the trip may be measured by the coal used up or the steam used, or something else. Now we will come back to a hydraulic anal- ogy. A current or stream of water is capable of running a water wheel or a water motor and doing work. Its power, or rate of doing work, depends on the “strength” of its current (i. e., 12 UNITS O F MEASUREMENT the amount of flow in a given time), and its “force” as measured by its pressure or head. Suppose you lived somewhere where there was no electricity and you connected a water motor to your kitchen faucet to run a washing machine. There would be a certain flow from the faucet which is under a certain pressure, say 50 pounds per square inch, and you get a certain power, or rate of doing work. Now, if you had a larger faucet and feed pipe, you would get a larger flow and you would expect more power or a faster rate of work. Or, if you kept to the original faucet but the town water pressure was increased, you would also expect more power. The -power would he proportional to both the flow and the pressure. So the power, or rate of doing work, in an electric circuit depends upon the same two factors; First, the strength of flow, or amperage; Second, the electric pressure, or voltage. In fact, the electric power is the product of these two factors. A watt then is that unit of power produced when one ampere flows in a circuit under a pressure of one volt. The watts may accordingly be found by simply multiplying the volts by the amperes as expressed in the following equation: W = V X A 13 EDISON SCHOOL OF SAI, ESMANSHIP For example: a standard 6-pound Hotpoint or Edison flatiron is rated at 110 volts and 5 3^ amperes. Then the Watts = V (110) X A (534) = 575 (approx.) The corresponding flatiron intended to be used on a 220 volt circuit, which is common in foreign countries, would be rated at 2^ am- peres. And the product of the volts and the amperes in this case would be 220 x 2^ = 605 watts — which gives approximately the same product and wattage as that of the 110 volt iron. The Watt-Hour We have been dealing with a measure of the rate of doing work, — the unit of power which is the watt. We need now to have a measure of the work actually done, or the electrical en- ergy expended, and this introduces the factor of time — the work done as measured hy the length of time the power is applied. If we apply a watt of power for one hour, we have a unit of work done which is called the watt-hour. The watt-hour may be defined then as the equivalent of one watt used for one hour. It may be only a half-watt used for two hours, or two watts used for only one-half hour; in fact, any combination that equals one watt for one hour. 14 UNITS O F MEASUREMENT It is easy to understand that two watts ap- plied for one-half hour will do the same work as one watt applied for one hour, just as two men might unload a carload of coal on a siding in one-half day, and one man would do the same job in a whole day. The work done would be the same in both cases. If H equals hours, or the length of time the power is applied, then WH = WxH or the power multiplied by the length of time. We have seen, however, that the power W is the product of the pressure and the current, or the volts times the amperes. Therefore WH = V X A X H which is saying that the work done, or the energy expended, depends on the length of time that a current is applied under a certain pressure. To illustrate: An appliance of 4 amperes 110 volts (like a Hotpoint or Edison Toaster) consumes 440 watts, that is, its rate of using power; if operated for one hour, it uses 440 watt- hours; for one-half hour, 220 watt-hours; for two hours, 880 watt-hours — that is, watt-hours is the measure of the work done. For example: WH =V(=110)xA(=4)xH(= 1) =440 WH = V ( =110) X A ( =4) xH ( =3/^) =220 WH = V ( = 110) X A ( =4) X H ( = 2) =880 IS EDISON SCHOOL OF SALESMANSHIP A watt is a measure of the rate of doing work. A watt-hour is the measure of energy actually expended, or amount of work done. The Kilowatt-Hour In commercial practice we do not use the watt-hour to measure electrical energy, because it is so small. We have accordingly adopted a unit of measurement which is 1000 watt-hours, called the kilowatt-hour, expressed KWH. The word kilo means 1000 and so the kilo- watt-hour is a thousand watts for one hour, or 250 watts for four hours, or 2000 watts for one-half hour, or one watt for 1000 hours; or any combination which is the equivalent of 1000 watts for one hour. This will explain what is meant when a bill for electricity reads 18 KWH @ 10c = 31.80. A kilowatt-hour or a thousand watts applied for one hour will operate for one hour, forty 25- watt Alazda Lamps, or two electric flatirons, or a one horsepower motor. But a kilowatt-hour will also operate for one- half hour, eighty 25-watt Mazda Lamps, or four electric flatirons, or a two horsepower motor. To go further, a kilowatt-hour will operate for six minutes, four hundred 25-watt Mazda Lamps, or twenty electric flatirons, or a ten horsepower motor. 16 UNITS OF MEASUREMENT The cost of operating will be the same in all three cases because the quantity of work done, or energy consumed, is the same — one kilowatt- hour. The Electric Lighting Company sells KWH — k i lo wa tt-hou r s . But the power, or rate of doing work, neces- sary in the last case would be ten kilowatts, in the second case it would be two kilow’atts, and in the first case, as already stated, it would be one kilowatt. Examples of Wattage You may easily apply what you have learned about watts by observing the markings on the name plates of electric appliances. Sometimes the amperes and volts are given, but usually the watts and volts are given. In the first instance, if a name plate on the appliance is marked “5 amperes 110 volts,” then you get the watts, of course, by multiplying 5x110, which will give you 550. Usually the manufacturers’ catalogs give the wattage and in this way you can check the ratings with the published information. The modern tendency, however, is to mark the watts directly on the name plate because that is what the user is most interested in. The amperes were formerly marked for the benefit of the electrician, who wanted to know the size 17 EDISON SCIIOOI. OF SALESMANSHIP To find the wattage of any electric appliance marked with amperes and volts use the following method: AMPERES X VOLTS = WATTS For example: 3 AMPERES X 110 VOLTS = 330 WATTS Therefore, such an appliance will con- sume 330 watt-hours of electricity if operated continuously for one hour of wire, which is determined by the amount of current and not by the wattage. However, if a name plate is marked “600 watts and 110 volts,” then if we wanted to find the amperes, our rule would be to divide the wattage by the volts according to the formula: and in this case A would equal 5.45 amperes. While the voltage is always marked on a name plate, we might have some case where we have the watts and the amperes and wanted to find the volts. The formula would then be: A and if the watts were 600 and the amperes 6, of course, the voltage would be 100. Another practical point is brought out by what we have learned about wattage. If you 18 UNITS OF MEASUREMENT take an appliance marked 110 volts and con- nect it on a 220-volt circuit, such as is occa- sionally found in this country, you get four times the power or wattage and will probably destroy the article. The resistance remains constant, because it is a definite quality of the design of the appli- ance, but doubling the voltage also doubles the current which flows through the appliance — and the wattage is the product of the two — hence you get four times the wattage. Now that you have finished Lesson Two, lay down the papers for a moment and review in your mind what you have read. Recall the three fundamental measurements of electricity, the ampere, the ohm, the volt. What do each of these represent.^ Go over the lesson mentally as far as possible. Then take up the lesson again, and be sure you have not missed any of the important principles, particularly those which are in italics — they are the key to the whole lesson. Now you are ready to answer the question sheet. 19 • s, PROBLEMS Part I ELECTRICITY LESSON I EDISON ELECTRIC APPLIANCE COMPANY, Inc. CHICAGO oStoiqa ‘was JojXex °99i ‘ANVdwoD aoNvnddv oiaxoaia Nosiaa/'^^a cIIHSNVI'^S31VS> 300HDS NOSIOa oj saijdaj jnoX sssappv •33B3yUJ33 B papjBMB aq jjim noX ‘asjnoa aqj jo uoijaiduioD Xjojdbjsijbs jnoX uodQ •noX OJ ujnjaj puB ‘SuipBjS B jadBd jnoX aAiS ‘luaqj jd3.uod ‘s.i3msub jnoX jsao o 8 piM 3^ •sn OJ J33qs wxsiqoJd ^qi JIBUI pUB ‘3JBp sqj pUB ‘U0IJ33UU03 SSSUISnq ‘SSSjppB ‘3UIBU jnoX u3[S •uoijsanb qoBS japun aoBds >[UB]q 3qj ui J3MSUB aqj Suijuav ‘jaaqg siqj uo sui3[qojd anoX JJJO^ •puiui UMO jnoX UI jB3p sjuiod 3S3qj jaS noX puB ‘uossaj qoBS jo Sfutod jUfUodtut jsoui aqj uo ajBjjuaauoD noX ‘suiajqojd aqj jjjoav noX uaq^ •suiajqojjj aqj uo j[joM jnoX SI asjnoQ siqj ui SumiBjj jnoX jo jjBd juBjjoduii jsom 3qj_ SMaiaoHd 3 HX moun /Oy; tvt/di jsnf oj j-» iunr tou suv otjoi 3soi{i uvt{i aftj m ua^Mf taS rXpuj/p ///m isai ai{i OJ a3pa;(nou^ ny sjni o^ai uvm at{X s Part I ELECTRICITY LESSON I EDISON ELECTRIC APPLIANCE COMPANY, Inc. CHICAGO QUESTIONS 1. What is the latest theory of the nature of electricity ? 2. What are the two forms of electricity ? How do they differ from each other? 3. How is current electricity produced ordinarily ? 4- Describe the formation of an electric current by a battery. What are the two kinds of primary batteries and how do they differ ? 5. What are the two kinds of current electricity ? 6. What IS a cycle ? What is meant by 60-cycle current ? 7. What is a conductor ? An insulator ? 8. What is an excellent insulating material for the heating elements of electrically heated appliances? Why? 9. Name some good conductors and some good insulators. i >, - "> I 'fySw, X?: '."'tl bri/''’'.':; •»;!'■ » Form 335-5221 EDISON SCHOOL OF SALESMANSHIP 5600 West Taylor Street CHICAGO, ILL. 1 . 2 . 3 . 4. 5. 6 . 7. 8 . 9 . ANSWERS TO QUESTIONS Assignment 1 - Part 1 The latest theory of nature of electricity is that it is a rapid vibration of the molecules of the conduc- tor and in the space immediately surrounding the conductor. See Page 6 - Paragraph 2 Static electricity, which is electricity at rest produced by friction, and current electricity, which is elec- tricity in motion. See Page 7 - Paragraph 2 Current electricity is ordinarily produced in two ways; by chemical action and by magnetism. See Page 9 - Paragraph 2 When the two poles of the ordinary "wet" battery, placed in a solution of sal-ammoniac or diluted sulphuric acid, are connected by a wire outside the liquid, electric energy is generated by the chemi- cal action of the acid on the metals and then flows through the wire, (b) The dry battery is practi- cally the same as the wet battery except that the solution exists in a dry paste form. See Page 1 0 - Paragraph 3; also Page 1 1 - Paragraph 2 Direct current flows continually in one direction; it starts from the positive pole and flows continually thru the circuit to the negative pole. Alternating current periodically changes its direction, flowing first in one direction completely through the circuit, and then in the opposite direction completely through the circuit. See Page 1 1 - Paragraph 4 One complete reversal of alternating current in a dynamo forward and backward, is known as a cycle. In some dynamos producing alternating current, the current makes 60 complete reversals or cycles per second, or makes 1 20 alternations per second. This is a 60-cycle dynamo. See Page 1 2 - Paragraph 3 Substances which allow electricity to pass through them readily are known as conductors. Those which materially resist the passage of electricity are known as non-conductors or insulators. See Page 1 3 - Paragraph 3 Mica; It is capable of withstanding high temperature and is a good conductor of heat. See Page 1 5 - Paragraph 5. Good conductors: Copper, silver, gold, aluminum- Good insulators: Dry air, glass, porcelain, mica. Third Assignment EDISON SCHOOL of SALESMANSHIP Part I ELECTRICITY Lesson III The Cost of Operation and Its Measurement EDISON ELECTRIC APPLIANCE COMPANY, Inc. CHICAGO Copyright 1921 Edison Electric Appliance Company, Inc. PROBLEMS Part I ELECTRICITY LESSON III STUDENT NUMBER STREET AND NUMBER OR P. O. ADDRESS EDISON ELECTRIC APPLIANCE CO., Inc. CHICAGO fo }pimi uo pinuituoo suoiu>nb fo }ftj) ilsoo aija aq ]jia\ jBqM ‘KM'S sjuaa 01 XjpujDaja qjiyW ^‘auiu siqa Suunp pauinsuoa uaaq SBq XiTouioap qontu AVOH spesJ IJ ^epoj^ '£9SZ Jajaui upuaD v jo Suip^aj aqi oSb qaaM auQ ’j ^•pasn Xapujaap p lunome aq^ jajsiSaj jaiaiu aqj saop juauiaansBaui p jiun jBqAV uj SNOiisaaO -i The man who puts his knowledge to the test will always get farther in life than those who are not sure as to just what they know PROBLEMS Part I THE PROBLEMS ELECTRICITY The most important part of your training in this Course is your work on the Problems. ■ When you work the problems, you concentrate on the most important points of each lesson, and you get these points clear in your own mind. Work your problems on this Sheet, writing the answer in the blank space under each question. Sign your name, address, business connection, and the date, and mail the Problem Sheet to us. We will go over your answers, correct them, give your paper a grading, and Upon your satisfactory completion of the course, you will be awarded a Address your replies to LESSON III EDISON SCHOOL of SALESMANSHIP Care of EDISON ELECTRIC APPLIANCE COMPANY, Inc. EDISON ELECTRIC APPLIANCE CO., Inc. 3. If the hand on the “Hundreds” dial in the illustration in this lesson (page 7) had been as it is now, but the hand on the “Tens” dial had pointed between 0 and 1, what would have been the reading of the meter? 4. An electric iron has a wattage of 575. A week’s ironing takes three hours, but the plug was out one-third of the time. How much does it cost to do the ironing with electricity at 10 cents per KWH? 5. A 110-volt toaster takes 4 amperes and toasts two slices of bread on both sides, in 5 minutes. What will be the cost of toasting 20 slices of bread on this toaster with elec- tricity at 10 cents per KWH? 6. An electric coffee percolator consumes 440 watts and makes 6 cups of coffee in fifteen minutes. How would you express the cost of operating the percolator to the customer and why? 7. If the electric meter should happen to be inaccurate, in which direction would the dis- crepancy usually be? The man who puts his knozvled^e to the test will always get farther in life than those who are not sure as to just what they know THE PROBLEMS The most important part of your training in this Course is your work on the Problems. When you work the problems, you concentrate on the most important points of each lesson, and you get these points clear in your own mind. Work your problems on this Sheet, writing the answer in the blank space under each question. Sign your name, address, business connection, and the date, and mail the Problem Sheet to us. We will go over your answers, correct them, give your paper a grading, and return to you. Upon your satisfactory completion of the course, you will be awarded a certificate. Address your replies to EDISON SCHOOL of SALESMANSHIP Care of EDISON ELECTRIC APPLIANCE COMPANY, Inc. 5660 Taylor Street, Chicago , .If iOii'r ; xri y Jvr, \ Edison School of Salesmanship 5600 WEST TAYLOR STREET CHICAGO, ILL. ANSWERS TO QUESTIONS 3 - Assignment # - Part 1 . The meter registers the amount of electricity used in KWH Kilowatt Hours. By subtracting 2563 from 2574, we get 1 1 KWH which is the amount of current used. If we multiply 1 1 (KWH) by the cost of electricity per KWH, or 10 cents, we get $1.10. 2380. 575 watts X 2 hours =1150 watt hours. 1 1 50 watt hours = 1.15 KWH. 1.15 KWHx 10 = 11.5. 110x4 = 440 watts. 20/2 = 10 X 5 = 50 minutes = 5/6 of 1 hour. 440 watts X 5/6 = 366 watt hours. 366 KWH x 10 cents = 3.66 cents. 400 X . 1 0 = 04 cents = cost of operation for one hour, 1 5 minutes or 1 /4 hour at .04 cents an hour = .0 1 cost of making six cups of coffee. Operation cost is most effectively express- ed to a customer by saying "one-sixth of a cent per cup" rather than by saying "24 cups per hour at a cost of 4 cents. In addition to being better selling psychology, this more closely expresses the actual cost of operation. The meter will register less than has been used. EDISON SCHOOL of SALESMANSHIP Part 1 ELECTRICITY Lesson III The Cost of Operation and Its Measurement D O you know how to read an electric meter? Do you know how to calculate the cost of operating any electrical appliance for any given length of time? These are points which may come up any time during your efforts to make a sale. Some- times sales are lost simply because the questions a prospective buyer asks can not be answered instantly and with conviction. Suppose a wom- an at whose home you called to make a sale said: “My bills for electricity are very unrea- sonable. I don’t know how the company figures them, but I know I do not use as much current as the company charges me for. How do they figure those bills ?” Could you answer 3 EDISON SCHOOI, OF SALESMANSHIP her satisfactorily? Could you take her to the electric meter in her home and show her how to figure her own bills? Let us take another point. Suppose during the process of making a sale on, let us say, an electric iron, the prospective purchaser said: “Yes, that may be a good iron, but I am told they take a lot of current. I am afraid it would be too expensive to operate.” Could you figure for that woman the exact cost of operating the appliance during an hour’s ironing? And could you do it in a way that would convince her? These are the important points covered by this lesson. Let us first take the electric meter. The Electric Meter (Watt-hour Meter) We have learned what very definite units there are by which electricity may be measured; and that the watt hour, or rather, the kilowatt hour, is the measure by which electricity is sold. (KWH = Kilowatt hour =1000 watt hours.) It measures the energy used, which is in exact pro- portion to the work done by the electric current. The various units of measurement of electricity can be very accurately recorded in commercial instruments, or meters. 4 THE COST OF OPERATION AND ITS MEASUREMENT In this lesson when we speak of the “meter,” we will refer only to the watt-hour meter,* which is the meter installed and connected in all premises that are wired for electric service. In principle, the electric meter is really only a small electric motor driving a set of dials, the motor being so designed as to revolve at a speed exactly proportional to the amount of electric energy being used. In the standard type of meters, the speed of the motor is regulated by a horizontal metal disc which revolves on jewel bearings between horseshoe magnets. Most meters are marked with the value in watt hours for each revolution of the disc. This figure may be found on the name plate or marked on the disc. In most types you can see this disc revolve. For example assume that one revolution of disc measures one watt hour. If one watt of elec- tricity were being used, the disc would revolve once an hour. When a 50-watt Mazda lamp is being used, the disc will make 50 revolutions in an hour. Or, if the lamp were on for one- fiftieth of an hour, the disc would revolve once and the meter would register one watt hour, or one one-thousandth of a kilowatt hour (KWH). *NOTE: — There are ether meters for measuring electricity, such as Ammeters, or Ampere meters, for measuring the flow of current; Voltmeters for measuring the pres- sure, or voltage; Wattmeters for measuring the rate of power used, etc. 5 EDISON SCHOOL OF SALESMANSHIP (Such a very small amount, of course, could not actually be observed on the dials of the ordinary meter.) Thus the moment an electric lamp, or any other current-consuming appliance connected on the circuit is switched on, this little motor begins to revolve, and at a speed in keeping with the wattage consumption of the appliance or appliances connected on the circuit. This motor has no work to do, except to revolve the metal disc referred to, and to move the little hands on the dials of the meter, which leave a record of the exact amount of electricity consumed. Accuracy of Electric Meter It is because this motor (unlike motors for operating sewing machines, washing machines, etc.) has practically no work to perform, that it can be very delicately and accurately made, and the weight of its rotating part is so small, and the bearings so delicate, that no measurable amount of energy is consumed in operating it. One peculiarity of the electric meter is that only dust and friction are at all likely to affect its accuracy, and both of these necessarily have a retarding effect, causing it to register less cur- rent than has been used. The chances of its registering more are remote indeed. 6 THE COST OF OPERATION AND ITS MEASUREMENT Meters in use in residences are often tested in large numbers, and it is exceedingly seldom that one is found that is appreciably inaccurate. How to Read a Meter Let us now turn to the dials of the meter and learn to read them, and be able at any time to determine how much electricity has been consumed in a given period. The meter is made to read in kilowatt hours. 2 3 8 6 A meter usually has four dials, as illustrated above. The dial at the right registers from one to ten, the units; the hand on this dial moves from one number to the next for each KWH and makes a complete revolution for every ten kilowatt hours. The second dial from the right indicates the tens, and its hand moves from one number to the next for each ten kilowatt hours used, and makes a complete circle for every one hundred kilowatt hours. 7 EDISON SCHOOL OF SALESMANSHIP The third dial from the right registers the hundreds, and the dial at the left, thousands. The little figures above the dials indicate the complete quantity which each dial registers. For example: We have stated that the second dial from the right measures tens, while the figure above the dial is “100.” This means that the dial will measure ten for each division and 100 when the hand goes completely around the circle. When the hand is approaching 0, it is ap- proaching 100 in value; when it is leaving 0, it is leaving zero in value; the hand on the next dial to the left — the hundreds hand — has moved around to the next figure and added a hundred more to the meter record, so that the tens hand begins at zero again, and starts re- cording tens to make up the next hundred. So with the units hand: it measures up to ten, and the instant it touches 0 it measures zero again, and starts to record the next ten. The ten just measured is now recorded by the tens hand. To read the meter, it is only necessary to write down the numbers registered on the dials, writing them in the same order as the dials on the meter, and always taking the smaller of the two numbers between which each hand points. We have applied this to the illustra- 8 THE COST OF OPERATION AND ITS MEASUREMENT tion (page 7) and placed the number below each dial, showing that the meter registers 2386. Sometimes the hand on the dial will appar- ently rest directly over the figure and yet, in Because the hand on the right- — you know that the hand on the left-hand dial has NOT passed hand dial has NOT passed O 2, and should be read as 1 /Tf'Yx 8) 1 V G l3 7J \7 3/ some cases, the next smaller figure should be used. Take the following illustration: When a hand is on top of a number (as in the dial shown at the left above) do not put down that number unless the hand on the dial to the Because the hand on the —you know that the hand on the left-hand dial has passed 2 right-hand dial has passed O 8' 1 r i H l3 7; ' V7 3 RIGHT of it has passed 0. If it has not, put down the next lower number. 9 EDISON SCHOOL OF SALESMANSHIP You will readily understand why this is. For instance, on any dial (except the one at the extreme right end, of course) the hand travels only one-tenth as fast as the hand on the dial to its right. Because of this slower movement, it is almost impossible to tell whether the hand has actually passed, or not quite passed the number it rests over. You will readily see that in the case of the third dial from the right (page 7) any error in judging the position of the hand would mean an error of 100 kilowatt hours. But in every case, even should the hand be slightly misplaced, and actually have passed the center of the number over which it is found, you can definitely determine which number to put down by noting the position of the hand at the right of it. There is another point about reading a meter which must now be brought out; that is, the registration on the dials of the meter gives a record of the total kilowatt hours since the meter started from zero. Take the meter dials in the illustration on page 7 which show that 2386 KWH have passed through the meter since the meter started from zero. Let us assume for illustration that the average family’s consumption of electricity is 30 kilowatt hours a month (if we assume the lighting rate is 10 cents per kilowatt hour, this would 10 THE COST OF OPERATION AND ITS MEASUREMENT represent a bill of i53.00 per month). In this meter, then, we have the total kilowatt hours consumed by such a family for 793^2 months, or more than six years. This meter will register until 10,000 kilowatt hours have been used, when it will continue to register but starting over again from zero. If we now assume that the meter man has just visited a residence where this meter is in- stalled, he will put down in his book the reading, 2386 kilowatt hours. The next time he comes around to read the meter we will assume that the dials then read 2417, which will show that 31 kilowatt hours have been used during the month. In other words, IT IS THE DIFFER- ENCE in monthly readings that is paid for. In Meter Reading It Is Only the Difference That Counts //, at one readin^y the meter dials register 23H(), and if one month later they are found to register 239S, then the amount of electricity consumed for the month is 239H — 2386 or J2 KWH To find out how much electricity has been used then, it is necessary to take two readings — ■ at the beginning and at the end of the period II EDISON SCHOOL OF SALESMANSHIP which it is desired to measure; it may be an hour, a day, a week, or a month. We have learned that the reading of the meter at any one time has nothing to do with the current consumed. Whether a new meter which may be installed registers 36 or 4628 is of no significance, as it is always the difference between two readings which represents the con- sumption of electricity. It is accordingly on this difference as shown on the meter readings that the lighting company bases its bills. How to Determine the Electricity Used Or the Wattage of an Appliance If it is desired to determine either the watt- age of a lamp or of an appliance, or the electricity used in a given time, it is only necessary to con- nect such lamp or appliance on a circuit to which a meter is connected and operate it over a given period of time. Suppose you wanted to know the amount of electricity consumed by a standard Hotpoint or Edison flatiron, you would first make sure that there were no lights or other electric appliances connected in the house. You can check this by looking at the meter and observing that the revolving disc on the meter is stationary. You 12 THE COST OF OPERATION AND ITS MEASUREMENT would then switch on your electric flatiron and make a note of the time and the reading on the meter dials. Let us assume that the meter reading is 2386 kilowatt hours. Let us suppose that you continued ironing two hours, and that part of this time the current was turned off to prevent the iron from becoming too hot. At the end of this time you would read the meter and might find that it registered 2387 KWH, which would show that the flatiron had consumed one KWH during the period of two hours’ ironing. (In this test only the hand on the dial on the right end would have moved perceptibly; i. e., from 6 to 7; the hand on the next dial would have moved only one-tenth as much; and the hand on the third dial one one-hundredth as much, and of course, could not be observed.) If you had used the iron for only one hour, you would have used only one-half KWH. If the current had been on the flatiron during the whole time, for two hours, the actual reading would have been 1.15 KWH (1150 watt hours). Now then, if we want to know the wattage rating of the flatiron we would take the watt hours consumed for one hour and this would give us 575 watts, which in fact, is the reading on the name plate of the flatiron. 13 EDISON SCHOOL OF SALESMANSHIP To find the wattage of an appliance by means of the meter, it is only necessary to have it reg- ister continuously on the meter for one hour., in which case the reading changed into watt hours is the measure of watts. If the electrical appliance is operated more than an hour, take the reading in kilowatt hours and change it into watt hours and divide by the number of hours the device is in operation. In the case of the flatiron just referred to we said that the meter reading would be 1.15 KWH in a period of two hours, therefore 1.15x 1,000 =b/b watts. In such cases the current must be on contin- uously. Determining the Cost of Operation When we have the meter readings, we find the cost of operation by multiplying the KWH by the rate charged per KWH. Throughout this course we will assume the rate charged by the Lighting Company to be 10 cents per KWH, which makes easy figuring (and as a matter of fact, is the rate usually charged for lighting purposes). It must be pointed out, however, that some companies have to charge more, while some can charge less, and some small 14 THE COST OF OPERATION AND ITS MEASUREMENT companies and those which operate for a short season of the year have to charge 15 and 20 cents per KWH, and even more. Many companies make a special rate for electric cooking of 3, 4 or 5 cents because it is “OFF PEAK” business, somewhat on the same principle that a lower charge is made for a matinee compared with an evening show. In the previous lesson we have learned how to find the wattage from the name plate mark- ings on an electrical appliance, and, when we have the watts, to find the watt hours by multiplying the watts by the hours the appli- ance is in use, or rather, the hours the electricity is actually flowing through it. From this we can estimate or determine the COST of operation by multiplying by the rate charged per KWH — in all our lessons, assumed to be 10 cents. Let us take a few more illustrations: Mazda lamps are rated in watts. There- fore, if a Mazda lamp is marked 25 watts you will know that in one hour this lamp consumes 25 watt hours or 14o kilowatt hours (25 divided by 1000). Therefore such a lamp would need to burn 40 hours to consume one kilowatt hour of electricity. Again consider a Hotpoint electric radiator stamped 600 watts. Such a radiator will accord- 15 EDISON SCHOOL OF SALESMANSHIP ingly consume or % kilowatt hours in one hour. With electricity at 10 cents per KWH the cost of operating this radiator would be % X 10 or 6 cents per hour. Many appliances, in place of being stamped in watts, have the voltage at which they are designed to operate and the amperage which they require stamped on them. As has been previously pointed out, to find the wattage of such an appliance it is only necessary to multi- Electric iron MADE BY ' Blank Electric Mfg. C o. AMPERES W3M VOLTS fTSl Illustration of name plate on a 3-lb. electric iron To find the wattage multiply amperes by volts: 3 amperes x 110 volts=330 watts or amount of current iron will consume if operated contin- uously for one hour ply the number of volts by the number of am- peres. For example, a three-pound electric iron stamped 110 volts 3 amperes would have a wattage of 330 watts per hour or approximately Vs KWH per hour. With the cost of current at 10 cents per KWH the cost of operating this iron would be 3^ 3 cents per hour if the current were on continuously. It should be here pointed out, however, that this would not be a correct result for the cost 16 THE COST OF OPERATION AND ITS MEASUREMENT of Operating such an iron for one hour even though our figures as to the wattage of the iron are correct. The reason why it cannot be stated definitely that the cost of operating the iron in the foregoing example is cents per hour is that this assumes that the current remains turned on during the entire hour. In many electrically heated appliances the current, however, is not flowing during the entire time that the appliances are in use, nor is it desirable to have it flowing continuously. The actual cost of operating them therefore is considerably less than would appear from simply figuring the amount of current used per hour when continuously connected to the circuit. In the case of well-designed 6-lb. irons it is not necessary to keep the current turned on continuously while the iron is being used. In ordinary practice the iron woidd be disconnected for about one-third of the time. The actual cost of operation would then be about 3^ cents per hour and not 5^ cents. Again: a good coffee percolator with a wattage of say 400, nominally consumes 4 cents worth of electricity per hour when the rate is 10 cents per KWH. This cost is insignifi- cant, however, when it is realized that in a percolator of this class it is possible to make 17 EDISON SCHOOL OF SALESMANSHIP six cups of coffee in 15 minutes or less, and that therefore the cost of current is but one cent for six cups. This is an important factor to remember in the selling of electrical appliances. Six cups of coffee for one cent — makes a far better impres- sion upon the prospective purchaser, and also very much better expresses the actual cost of operating the appliance, than to name the amount it would cost to operate it for an hour. 18 THE COST OF OPERATION AND ITS MEASUREMENT Use the information you have gained in this lesson at the very first opportunity. Put it to work. That is the way to get the most out of this course. Use it. Fourth Assignment EDISON SCHOOL of SALESMANSHIP Part I ELECTRICITY Lesson IV ABOUT Circuits EDISON ELECTRIC APPLIANCE COMPANY, Inc. CHICAGO Have the utmost confidence in yourself and in the electrical goods you are selling. Keep in mind at all times that you cannot accom.plish anything in greater measure than the measure of your confidence in it. This is true no matter what your ability, your education or your knowledge of electrical appliances. Success comes more certainly to the salesman who believes in himself and in his firm and in the goods he is selling. Copyright 1921 Edison Electric Appliance Company, Inc. PROBLEMS Part I ELECTRICITY LESSON IV NAME STUDENT NUMBER STREET AND NUMBER OR P. O. ADDRESS CITV STATE EDISON ELECTRIC APPLIANCE COMPANY, Inc. CHICAGO jsaouBijdde auioij jEDuioap ui ajqnojj asnso ji saop Avojq pjc uk si •£ •jojFjauaS gqi oj 5jDBq puB uiaisXs B qSnojqj jno JoaBjauaS aqi uiojj qaBd jEauiaap ub Xyauq aoBij^ 'Z ^ uado II SI uaq^w ^‘pasop it si uaq^ jiinajp auiaaja ub si aBqy\\ 'i SNOiisaaO The man who puts his knowledge to the test will always get farther in life than those who are not sure as to just what they know PROBLEMS Part I THE PROBLEMS The most important part of your training in this Course is your work on the Problems. When you work the problems, you concentrate on the most important points of each jesson, and you get these points clear in your own mind. Work your problems on this Sheet, writing the answer in the blank space under each question. Sign your name, address, business connection, and the date, and mail the Problem Sheet to us. . We will go over your answers, correct them, give your paper a grading, and Upon your satisfactory completion of the course, you will be awarded a Address your replies to ELECTRICITY LESSON IV ^ EDISON ELECTRIC APPLIANCE CO.MPANY, Inc. EDISON SCHOOL of SALESMANSHIP Care of EDISON ELECTRIC APPLIANCE COMPANY, Inc. 5600 West Taylor Street, Chicago CHICAGO 4. Write an essay of one hundred words or not more than two hundred, on short cir- cuits. Use only those facts that are of interest to women customers. 5. There are how many kinds of electric circuits from the standpoint of wiring.? Name and illustrate each one. 6. Illustrate the connections of a Hotpoint three-heat grill. Explain how LOW, MEDIUM and HIGH heats are obtained. 7. What is meant by voltage drop? . 8. Name four types of circuits usually used in cities and the voltage that each employs. How is high voltage changed to low voltage so that it can be used in ordinary residence wiring? 9. What is the advantage of a three-wire system? 10. Tell briefly how injury can come from electric shocks. The man who puts his knowledge to the test will always get farther in life than those who are not sure as to just what they know THE PROBLEMS The most important part of your training in this Course is your work on the Problems. When you work the problems, you concentrate on the most important points of each lesson, and you get these points clear in your own mind. Work your problems on this Sheet, writing the answer in the blank space under each question. Sign your name, address, business connection, and the date, and mail the Problem Sheet to us. We will go over your answers, correct them, give your paper a grading, and return to you. Upon your satisfactory completion of the course, you will be awarded a certificate. Address your replies to EDISON SCHOOL of SALESMANSHIP Care of EDISON ELECTRIC APPLIANCE COMPANY, Inc. 5600 West Taylor Street, Chicago Edison School of Salesmanship 5600 WEST TAYLOR STREET CHICAGO, ILL. ANSWERS TO QUESTIONS Assignment 4 - Part 1 . 1. An electric circuit is a conducting path, along which electric current flows from the source through the wires and appliances which make up the path, back to its starting point. A closed circuit is a complete and continuous con- ducting path. An open circuit is a circuit which has a break or gap in it, preventing the current from flowing. See Pages 3, 4, 7. 2. The current leaves the generator at the power station, travels over an insulated wire, suspended from poles insulated with glass or porcelain insulators, through the meter, through the appliances, and finally through second wire to its source in power house. See Pages 5, 6, 7. 3. An arc is a break in a wire. Arcing trouble in electrical home appliances are, for instance, a broken filament in an incandescent lamp, a broken conductor in a flexible cord, a melted fuse, a break in the wire composing the heating element of an appliance, etc. See Pages 8, 9. 4. This answer may best be put in student’s own words. Points that should be touched upon are: 1 . Explanation of a short circuit. 2. Need of careful insulation to prevent short circuits. 3. Accidental short circuits. 4. Paitial short circuits. 5. Grounded circuits. See Pages 9, 10, II, 12. . 5. Series and multiple circuits. In series circuit, exactly the same uniform current flows through the entire circuit. In multiple circuits, the current flows in parallel branches and divides itself into these branches in proportion to their relative conductivity. See Pages 1 4, 20. See illustrations Pages 1 4 and 22. 6. See Pages 1 5 and 2 1 of the text. 7. Voltage drop is the loss of voltage due to the resistance overcome in performing work. See Pages 16, 17, 18, 19 and 20. 8. Series circuit, trolley or street-car power circuit, power circuit for factories, and incandescent lighting circuit See Page 24. High voltage is changed to low voltage for use in ordinary residences by means of transformers. See Pages 27 and 28. 9. Three wire system reduces cost of local distribution system. See Page 28 10. Injury resulting from electric shocks usually occurs in connection with high voltage conductors. Bad bums often result but injuries are not usually fatal except where heart failure is induced. See Pages 30 and 31. EDISON SCHOOL 0/ SALESMANSHIP Part I ELECTRICITY Lesson IV About Circuits I N this lesson we will discuss some of the important facts and principles of Electric Circuits. We will consider them in a brief prac- tical way, from the standpoint of the electric appliance salesman. The following sections will contain an outline study of: Complete or Closed Circuits, Open Circuits, Short Circuits, Voltage Drop, Distribution Systems, and Shocks. The Complete or Closed Circuit An electric circuit is a conducting path (usu- ally a metallic wire) along which electric current flows from the source through the wires and 3 EDISON SCHOOL OF SALESMANSHIP appliances which make up the path, back to its starting point. Now refer to our previous analogy of elec- tricity and the flow of water. A break in a pipe will not stop the water from flowing, but a break in the wire path will prevent electricity from flowing. In other words, in order to have any flow of electricity, we must have a complete and con- tinuous conducting path. If a wire breaks, and an air gap is formed, the electric flow stops. You will remember that in our first lesson, dry air was placed at the head of the list of insulators. It is interesting to note here that it takes at least 1000 volts to jump an air gap of 1/20 of an inch, and 20,000 volts or more to jump one inch. Think of the immense voltage of a lightning discharge — billions of volts! (The amperage, of course, is very low.) Wires are called “live” when connected to a source of electricity, even though no current flows in them. The voltage pressure is there and the current is instantly ready to flow when the circuit is closed or completed by any means whatever. Live wires give a “shock” to the person touching them when the circuit is closed by the body and the current flows through it. 4 ABOUT CIRCUITS The Electric Circuit Traced from the Power Station Through a Home Diagram of a Commercial Circuit, Showing Various Sub-circuits In our reference to a circuit we have so far spoken only of a simple circuit. In commercial practice, however, the circuits are composed of many sub-circuits. The current that enters a private home is a sub-circuit, which in its turn also, is divided into other sub-circuits. The same rule that applies to the entire cir- cuit, applies to any sub-circuit or bypath: that is, the circuit will only flow in the bypath when the conducting path is absolutely without any break from beginning to end. The following interesting paragraphs are taken from Harper’s Beginning Electricity de- scribing the typical “Electrical Path.” “The current leaves the generator at the power station in a steady flow and under con- 5 EDISON SCHOOL OF SALESMANSHIP siderable pressure. This current travels over an insulated wire out in the street at the rate of 186,000 miles a second. These wires, though of the best copper, offer some resistance to the flow, and to overcome this resistance the elec- tricity loses some of its voltage, or pressure. “At every point where the wires are sus- pended from the poles they must be insulated with heavy glass or porcelain insulators, or it would jump off and short circuit back to the power house. “The current enters the house over a copper wire carefully insulated with rubber and further protected with porcelain tubes where it goes through beams, walls, floors, etc. This wire leads it to the watt-hour meter, which de- termines how m,uch electricity is being used. From the meter the current flows along a copper wire, hidden away in the walls of the house, to the electric-lamp fixture. Here it encounters an incandescent lamp, or even two or three lamps. The filament in the lamp is a very small tungsten wire, looped many times. This wire is no larger than a hair. It offers considerable resistance to the passage of the current. But there is ample pressure, or voltage, to force the current through it. In overcoming this resistance the wire is made white hot. All substances emit light when brought to a white heat. With some 6 ABOUT CIRCUITS of its voltage lost* in overcoming the resistance in the lamp, or lamps, the current begins its return journey. “Parallel with the wire which conducted it into the house and through the walls is another copper wire of the same size. This wire is placed about three inches from the other wire. It is also carefully insulated The current leaves the house by this second wire, which also passes through the meter, and continues down the street over another wire back to its source in the power house.” It is interesting to note that with alternating current — which is most commonly used — the electricity reverses its direction of flow usually every one one-hundred-and-twentieth of a second. In other words, the current would flow over the wires as just described for 1/ 120th part of a second and then would flow back over the second wire, returning to the power house over the first wire, and so on, making sixty complete cycles every second. Open Circuit An open circuit is a circuit which has a break or gap in it, preventing the current from flowing. A circuit is opened, for instance, whenever the electric current is turned off by means of a switch. *As a matter of fact, nearly all of its voltage is used up, only enough remaining to overcome the slight resistance of the return circuit. 7 EDISON SCIIOOI. OF SALESMANSHIP A switch is a device by which a gap in an electric circuit is closed or opened. It has a con- ducting member which bridges or closes the gap when it is desired to have the current flow. When it is desired to stop the current, this bridge is turned or moved, so as to open the gap. A Knife Switch The attachment plug (on the end of a flex- ible connecting “cord”), by means of which we connect (or disconnect) a lamp or an appliance to the circuit, is really a form of switch. When we unscrew the plug or pull it out, we have made the gap which interrupts the flow of the current. Accidently opened circuits may be occasioned by a broken filament in an incandescent lamp, a broken conductor in a flexible cord, a melted fuse, a break in the wire composing the heating element of an appliance or any accidental break in any part of the electric circuit. There are three common troubles affecting an electric circuit: unintentional open circuits; arcing which occurs accidentally; short circuits; and grounded circuits. 8 ABOUT CIRCUITS Arcing A break in a wire may cause a spark or an arc. Two live wires brought together and sep- arated slightly will make a spark or an arc, for the current will continue to flow by jumping across the gap. A “spark” is simply the elec- tricity apparent in the air jumping a gap. An “arc” is produced when sufficient current is flowing to cause the metal ends of the conductor, not too widely separated, to volatilize and pro- vide a conducting stream of metal vapor. It is very hot. In ordinary practice, every time a switch is opened, an arc tends to form. This is overcome by having “snap” or “quick break” switches. The switches open so quickly, the arc is instan- taneously interrupted. Arcing is a cause of trouble on flatiron con- tacts; it also causes trouble at the brushes in motors. On the other hand, this phenomenon is the principle utilized in arc lam.ps, which are used for street lighting, and in arc welding and metal cutting and melting. (The temperature of the arc in carbon arc lamps is about 6000°F.) Short Circuits Electricity always follows a path of least re- sistance, and in branch circuits the current will divide itself in inverse proportion to the resist- 9 EDISON SCHOOL OF SALESMANSHIP ance in the various branches. Therefore, if there are two branches, the branch which has the lower resistance will allow the most current to how through it. If the two wires of an ordinary household circuit should come in accidental contact, a path of very low resistance is provided where they touch, and the electricity in the circuit will tend to flow through this point in preference to flow- ing through the lamps and appliances in the cir- cuit which provide a path of comparatively high resistance. The current would take the shorter and easier path and the appliances and lamps would thus become “short-circuited.” Of course some current, even though a negli- gible amount, will continue to flow through the original circuit, for the current will divide itself in proportion to the conductivity of the various paths. A short circuit might occur even when the wires do not come actually together but when a metallic path of very low resistance is provided. For example, one might drop a screw-driver ac- cidently across the two bare wires of the circuit, and this would have the same effect as if the wires were actually in contact. Electric conductors must therefore be care- fully insulated from one another by means of 10 ABOUT CIRCUITS rubber or other insulation, or be supported by insulators such as porcelain or glass, and guarded from accidental contact. {Illustration No. 3) Accidental Short Circuits Bare wires separated one from another would be naturally insulated by the atmosphere but they would be exposed to accidental short circuit, unless properly guarded. In practice we refer even to partial short circuits as short circuits. Any unintentional or accidental diversion of the current by any means is included in the term short circuits, even though the short may be of high resistance. A very high resistance type of short circuit is usually referred to as a “leak.” This is because the high resistance prevents any great amount of the total current flowing from being shorted. A very low resistance type of short circuit is usually referred to as a “dead” short circuit, be- cause most of the current flowing passes through this short. The word “dead” in this case is only II EDISON SCHOOL OF SALESMANSHIP used for emphasis, as the circuit is very m.uch “alive” in another sense. It should be remembered that water is also a partial conductor of electricity. For that rea- son, conductors of electrical current are so ar- ranged that no wet material will reach from one wire to the other. For exam.ple, take the bell-like shape of nearly all insulators carrying wires on poles. These insulators are thus designed so that when it rains the water drops from the edge of the bell and cannot form a continuous wet surface from one wire to another. A short circuit is real “trouble” and must be repaired whenever it occurs, to save the current going to waste, or to insure all of the current passing through the appliance. Grounded Circuits Not only must two conductors be kept in- sulated from each other, but from the ground, or earth, as well ; for the earth is a conductor when a good “ground” or contact is made. When a conductor touches a water-pipe, gas-pipe, lightning rod, or any other metal that is connected to moist earth, part of the current will be diverted through this path to the earth, provided the other side of the circuit is also 12 ABOUT CIRCUITS grounded. The earth, with two “grounds,” makes a complete circuit or bypath. See lower drawing in illustration No. 4. BATre-ay' G/^oa/s/OS TO OtSTA/^T TE.UeGRAPH ST A AAAAAA/' CIRCUn GROUNDED INTENTIONALLY How Circuits Are Grounded In telegraph circuits, the ground is utilized as the return conductor, as shown in illustration No. 4, (upper drawing). Different Kinds of Circuits There are two kinds of circuits: one is the series circuit, and the other is the parallel or multiple circuit. 13 EDISON SCHOOL OF SALESMANSHIP The Series Circuit In a series circuit, exactly the same uniform current flows through the entire circuit. This is best illustrated in a diagram. Thus the current goes through one lam,p and then the other, and so on, and the voltage or pressure, is used up successively. If these lamps are 3^ ampere and 110 volts each, then the volt- age would drop 110 volts in each lamp, or 440 volts in the series of four lamps. But the same 3/2 ampere would flow through them all. This series system of current distribution is used chiefly in street lighting; in Xmas tree lighting sets; and in the internal connections of heating appliances. In a series circuit, any break — as in one of the lamp filaments in the diagram — interrupts the current flow in the entire circuit and all the lights will go out. In street lighting systems, special contrivances provide for the bridging of the gap when a light fails, so as not to have all the lights on the circuit go out. 14 ABOUT CIRCUITS How Various Heats Are Obtained Nearly all two or three-heat appliances have two complete heating coils or sets of coils. The low “heat” is obtained by connecting these sets of coils in series. B medium meat : on^ one coil Set in use. A {Illustration No. 6) Diagram of Wiring in a Three-heat Hotpoint Grill* As shown in the above diagram A, of a three- heat grill, to get low heat, the current must first go through one set of coils and then through the other. The effect is to double the length of the resistance wire, or to double the resistance of the circuit. The total resistance of a series circuit is equal to the sum of its farts. In a 600-watt, 100 volt grill each of the two sets of coils consumes one-half of the watts or 300 watts. Therefore, each has a resistance of *For simplicity the diagram shows but two coils. Actually in a Hotpoint grill there are eight coils — four in each set. 15 EDISON SCHOOL OF SALESMANSHIP When both sets of coils are joined in series, and the grill is connected to a 100 volt circuit, the current has to flow over twice 33 ohms, or 66 ohms and therefore only or amperes will flow. (V-j-0=A). Consequently only 100x13^ or 150 watts will be consumed. (V x A =W). Note that 150 watts is 3^ of 600 watts. There- fore with both sets of coils switched on in series the appliance is generating low heat. Now in order to secure a medium heat, one of the sets of coils is cut out (not used) so that the current flows through only one set. (Dia- gram B, see previous page.) This in effect reduces the resistance one-half and more current flows and more heat is generated. The method that produces high heat is ex- plained in detail in the second section following under the heading “The Parallel or Multiple Circuit.” Voltage Drop In considering voltage drop think what electricity does in a circuit. THE WORK OF ELECTRICITY IS OVERCOMING RESISTANCE. In fact, work of all kinds is the overcoming of resistance. 16 ABOUT CIRCUITS There are two forms of resistance in electric circuits : 1st — Resistance which is a quality of the con- ductor itself, and which varies directly as the length and inversely as the cross section of the conductor. 2d — Resistance due to a back pressure or counter-voltage which develops in electromag- netic apparatus such as motors and transformers. Work is done in overcoming either or both of these above forms. In overcoming resistance in any circuit, it is the electromotive force or the voltage pressure that is used up and not the amperage or the current. For instance, when a current of one ampere under a pressure of 100 volts is sent from a battery or dynamo out over a wire to do useful work it returns, after its work is completed, to the generator, still with a cur- rent strength of one ampere but with no pres- sure or force. It has suffered a drop in voltage because of the work done. Rule : The voltage drop is proportional to the resistance overcome. Let us illustrate this by a water motor at- tached to a faucet. The stream of water that comes out of the motor is the same stream that goes in; it has the same flow in gallons per hour 17 EDISON SCHOOL OF SALESMANSHIP but it has lost its pressure or “live” force. It goes in perhaps at a pressure of 50 pounds per square inch and com,es out at a pressure of 10, 5, or perhaps 0 pounds, depending on the power used by the m.otor. Rule : Voltage drop also is proportional to the current flowing. For if it takes 100 volts to force 2 amperes through a circuit of 50 ohm.s, the voltage drop is 100 volts; then obviously it will take double the volts to force 4 amperes through the same circuit, and the voltage drop will be 200 volts. We may cofnbine the two foregoing rules and state: The voltage drop is proportional both to the resistance and the current. These principles are illustrated in the fol- lowing diagram of a series circuit consisting of 5 lamps, each having a resistance of 40 ohms, and 2 heaters, each with 15 ohms resistance. There are 2 amperes flowing. {Illustration No. 7) Showing Voltage Drop Through Lamps and Heaters In Series 18 ABOUT CIRCUITS The following examples show how the total resistance is found; how the voltage drop and the wattage consumption is determined. 5 lamps, 40 ohms = 200 ohms 2 heaters, 15 ohms. . . . = 30 ohms Circuit Wires, 1 ohm, . . = 1 ohm Total Resistance . . . 231 ohms Ohms X Amp. = Volts Drop due to lamps .... 200 X 2 = 400 Drop due to heaters . . . 30 X 2 = 60 Drop due to wires 1 X 2 = 2 Voltage Drop (total) 231 X 2 = 462 Volts X Amp. = Watts Watts used in lamps . . 400 X 2 = 800 Watts used in heaters 60 X 2 = 120 Watts used in wires. . 2 X 2=4 Total Watts used . . 462 X 2 = 924 In our example (page 15) of the three-heat grill, with two sets of coils in series, having a total resistance of 66 ohms, each set having 33 ohms, the voltage drop will be 50 volts in each set. Closely associated with voltage drop is energy loss. It is measured in watts, and is the product of the voltage drop multiplied by the amperes flowing. The relation between volts used up and watts (or energy) used up is shown in the foregoing examples. 19 EDISON SCHOOL OF SALESMANSHIP The energy loss in watts may also be com- puted directly from the current because it varies as the square of the amperes flowing multiplied by the ohms resistance of the circuit or part of the circuit in question. This follows from the fact that W =VxA and V =AxO. Therefore substituting the equivalent of V, which is A x 0, into the formula W =V x A, we have Watts = A X O X A =A^O. This is also apparent from the example on the preceding page: 924 watts is seen to be the product of the ohms (231) times the amperes taken twice (2 times 2). The Parallel or Multiple Circuit In this form of circuit, the current flows in parallel branches, or in a multiple of branches or bypaths and the current divides itself into these bypaths or branches in proportion to their relative conductivity, or, to put it the other way around, the current divides in inverse proportion to their relative resistance. Consider a two branch circuit of equal con- ductivity or resistance. The two sets of coils in a grill, as in most “three-heat” appliances, make a good example. The diagram on the opposite page shows the coils in parallel, or multiple, as connected for high heat. 20 ABOUT CIRCUITS WwwV HIGti MEAT : both sets of Coils in use in par- ollel. {Illustration No. 8) The Diagram Shows the Wiring Method, and Path of the Current for High Heat in a Hotpoint Grill Heating Unit {Compare illustration No. 6) In this case it is easier for the current to flow in two paths than in one, in fact, it is twice as easy. This is equivalent to doubling the area of the cross section of one of the coils, which could be done by twisting the wires tightly together and into one cable. The result would be a wire 33 or 16.5 or cable which would make a coil of - ohms. ^ Putting it another way, each coil or set of coils in the grill carries -jy =3.3 amperes, for amperes = voltage Therefore the two sets of coils carry resistance 6.6 amperes or 660 watts, for watts equal the voltage multiplied by the amperage. Let us see how. Neglecting the voltage drop in the leads or wiring to the grill, and assuming the voltage at the grill to be exactly 100, then each “coil” is so connected that each receives 100 21 EDISON SCHOOL OF SALESMANSHIP volts pressure and there is a voltage drop of 100 in each; and as each coil has a resistance of 33 ohms, a current of 3.3 amperes will flow through each one at the same time; so there will be a total of 6.6 am.peres, or 660 watts. (If the sets of coils were connected in series, the voltage drop would be 50 in each coil and, as we have seen, only 1.65 amperes would flow — first through one coil and then the other.) Rule : In a multiple {or parallel) circuit of two branches, each having equal resistance or con- ductivity, the combined conductivity of the circuit is double and the combined resistance- is one-half. In a multiple circuit of three branches of equal resistance or conductivity, the combined conduc- tivity is trebled and the resistance is one-third. Corresponding rules apply to multiple cir- cuits of various numbers of branches of equal resistance. A Multiple Circuit with Two Branches of Unequal Resistance In multiple circuits with branches of unequal resistance, analysis is more complicated and the 22 ABOUT CIRCUITS full explanation lies outside the scope of this course; but one example may be given. Let us suppose a parallel circuit as illustrated. Branch “B” has twice the resistance of “A” and therefore one-half the conductivity. Let “A” have 5 ohms and “B” 10 ohms, and the voltage drop 100 volts. Then = 20 amperes will flow in “A” and = 10 amperes will flow in “B”; and 30 amperes will flow in both. The combined resistance is equal to the voltage di- vided by the combined current: =3.3 ohms. If both branches were 5 ohms each, the result would be 2.5 ohm,s; if 10 ohms each, it would be 5 ohms. Distribution Systems The illustration on page 5, which is a dia- gram of a distributing circuit of a power house or central station, is of course a multiple circuit of many branches. In cities and towns there are usually four im- portant major circuits going out from the power house or central station. First'. Street lighting such as arc or in- candescent lamps. This is a series circuit. The voltage depends 23 EDISON S C II O O I, OF SALESMANSHIP on the number of lamps in series up to approx- imately 2000 volts. Second: The trolley or street-car power cir- cuit. This is usually a 500 or 600 volt circuit of direct current, as street-car motors are direct current motors. Third: Power circuit which supplies the power load of motors in factories. Usually it is 220 or 440 volts. Fourth: Incandescent lighting circuit used in homes and buildings. This is a 110 volt circuit. (See section on three-wire distribution, following.) The Current in the Trolley Wire Flows Down the Trolley Pole Through the Motor, Through the Wheels to the Track and Back to the Generator The voltages referred to above are used in local circuits. These circuits are fed by high tension feeders from the power house carrying a current of higher voltage which is reduced to the required voltage by transformers. 24 ABOUT CIRCUITS Telegraph, telephone, burglar alarm and fire alarm circuits are not part of the Central Sta- tion Distribution System. These are low voltage circuits supplied from batteries or low voltage dynamos, although the Central Station may in some cases furnish the electricity to supply storage batteries or to operate motors which drive these low voltage generators. To prevent voltage drop in a distribution sys- tem the main branches, lines and feeders carry- ing the current to the sub-circuits are made large enough and with sufficiently low resistance to prevent any serious voltage drop. This in order: 1st — To maintain the proper voltage in homes and buildings no matter how many lights or appliances are turned on. 2d — ^To prevent a waste of electrical energy, which the voltage drop multiplied by the current represents. A Sub-branch Multiple Circuit The Central Station or light company is not responsible for the wiring within a building. Of 25 EDISON SC HOOT, OF SALESMANSHIP course, the wires should be sufficiently large to carry the current required. Every time a switch is turned on in a mul- tiple circuit, it provides another bypath, and allows more current to flow in the main circuit, for each additional lamp burning requires an additional 3^ ampere and a flatiron 5 or 6 amperes. The resistance of the multiple sub-circuits varies inversely according to the number of ap- pliances in use; i. e., their total resistance. (The resistance of the main leads and feeders, of course, is in series with the sub-branch cir- cuits and is constant.) The voltage drop, as we have learned, varies with the current flowing. When the current is increased in the main leads and feeders, more voltage is required to force the current through the wires and overcome their resistance; there- fore the greater the current the greater the voltage drop. There is, of course, a practical limit to the size of conductors used for mains and feeders, which is determined by their cost and the interest charge on the investment. In cities and towns a voltage drop of 5% is usually allowed. In long, high voltage trans- mission lines a very much larger drop is allowed. 26 ABOUT CIRCUITS This brings up a very important point in the transmission of power, the advantages of high voltage for transmission. Modern Steel Towers Carrying High Tension Electricity Across Country Power is the product of V x A. The voltage of transmission does not depend on the size of the wire, although the current does. (The volt- age which may be transmitted depends on the insulation used.) One KW or 100 KW may be transmitted over the same wire, provided it is properly insulated! At 100 volts, 10 amperes will produce 1 KW. At 10,000 volts, 10 am- peres will produce 100 times as much, or lOOKW. But the same wire properly insulated will carry either. That is, with the same loss or voltage drop in transmitting. If we allow 5 volts drop in the first case, 950 watts will be delivered, or 5% lost. In the second case, with 5 volts drop, 99,950 watts will be delivered, or only .005% lost! Alternating current can be easily transformed 27 EDISON SCHOOL OF SALESMANSHIP by means of transformers from one voltage to another, up or down, and is generally used in transmitting power over distances of a mile or so. In fact, it is superseding direct current almost entirely for lighting and power. It is not uncommon to transmit electric power over long distances at 100,000 volts or more. Three-wire System There is another way in which the cost of a local distribution system can be reduced and that is by the three-wire system introduced by Edison. {Illustration No. 13) A Simple Three-wire System For example: Two 110 volt dynamos or gen- erators are connected in series so the voltage between the outside wires “A” and “C” is 220 V. Yet the system provides for 110 volt service in the homes and the use of 110 volt lamps and appliances. If the two “sides” are perfectly balanced, both have the same resistance, and no current will flow back to the generators through “B;” and “B,” which is the middle or neutral wire. 28 ABOUT CIRCUITS has only to be large enough to carry the unbalanced current. “A” and “C” only carry a current equal to one-half that required to supply the same num- ber of lamps and appliances in two ordinary 110 volt multiple two-wire circuits. So, a great sav- ing in conductors m,ay be made. It is a combination series-multiple circuit. It has practically the advantage of a 220 volt mul- tiple system., and the effect is accom.plished by placing one group of 110 volt lamps and appli- ances in series with another group of 110 volt lamps and appliances. When the load on each side is balanced “B” serves merely as a “bus,” that is, a comm,on con- nector between the lamps on one side and those on the other, connecting them in series. If there is a difference in the loads, then “B” will carry the difference. In most cities and towns alternating current is generated and distributed at 2300 volts to the {Illustration No. 14) Diagram of High T ension Wiring with Step Down Transformer, Enabling Use of High Voltage Generator and Low Voltage Secondary Circuits 29 EDISON SCHOOL OF SALESMANSHIP various centers of distribution, usually on each block, where transformers step it down to 110 and 220 volts for distribution to the various houses and buildings on the block, over local 1 10-220 volt three -wire circuits. Electricity and the Human Body The resistance of the body to the passage of electric current may be as much as 100,000 ohms. This resistance is chiefly in the outer skin. The dry hands of a workman whose skin is tough and horny have many times the resist- ance of the moist hands of a person whose skin is thin and tender. One cannot feel the current, for example, from an ordinary battery or dry cell, because the cell has only l^^ volt pressure and assuming the resistance of the body to be 100,000 ohms it is evident that only \}/2 millionths of an ampere can flow, which is not enough to produce sen- sation. If the wires from a dry cell are placed to the tip of .the tongue the current can be felt slightly. In this case the resistance through the tongue might be about 1500 ohms, and therefore one thousandth part of an ampere would flow. If the two conductors of a 110 volt circuit are touched with dry Angers, probably one thou- sandth of an ampere will flow, which would 30 ABOUT CIRCUITS hardly be felt. If the fingers are moistened and the conductors touched, a slight shock and a twitching of the muscles may be felt. Severe high voltage shocks produce uncon- sciousness similar to drowning, and the person usually can be resuscitated if properly treated in time, although heart failure may result. Body shock then, depends upon the number of amperes which are forced through the body, and not directly upon the voltage. A heavy current also produces bad burns. The sparks which come from a comb on a cold day when combing the hair may be 1000 volts; the sparks from a rapidly moving leather belt may be 50,000 volts or more, but the momentary current flowing in each case is inflnitesim,al and therefore perfectly harmless. There is no danger then in the ordinary house circuit, under ordi- nary circumstances. Persons have been shocked beyond resusci- tation by standing in a bathtub and touching the metal part of an improperly insulated elec- tric light socket. In this case there was a “ground” on the circuit and the body made connection complete from the socket through the body to the water to the water pipes to the earth and then to the other leak or “ground.” (See page 13 about grounds on both sides of the circuit.) 31