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Audel Electrician’s Pocket Manual All New Second Edition Paul Rosenberg

Audel Electrician’s Pocket Manual - Paul Rosenberg

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  • Audel

    ElectriciansPocket Manual

    All New Second Edition

    Paul Rosenberg

  • Audel

    ElectriciansPocket Manual

  • Audel

    ElectriciansPocket Manual

    All New Second Edition

    Paul Rosenberg

  • Vice President and Executive Publisher: Bob IpsenPublisher: Joe WikertSenior Editor: Katie FeltmanDevelopmental Editor: Regina BrooksEditorial Manager: Kathryn A. MalmProduction Editor: Angela SmithText Design & Composition: Wiley Composition Services

    Copyright 2003 by Wiley Publishing, Inc. All rights reserved.Copyright 1997 by Paul Rosenberg.

    Published simultaneously in Canada

    No part of this publication may be reproduced, stored in a retrieval system, or transmitted inany form or by any means, electronic, mechanical, photocopying, recording, scanning, orotherwise, except as permitted under Section 107 or 108 of the 1976 United States CopyrightAct, without either the prior written permission of the Publisher, or authorization throughpayment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600. Requests to thePublisher for permission should be addressed to the Legal Department, Wiley Publishing,Inc., 10475 Crosspoint Blvd., Indianapolis, IN 46256, (317) 572-3447, fax (317) 572-4447,E-mail: [email protected].

    Limit of Liability/Disclaimer of Warranty: While the publisher and author have used theirbest efforts in preparing this book, they make no representations or warranties with respectto the accuracy or completeness of the contents of this book and specifically disclaim anyimplied warranties of merchantability or fitness for a particular purpose. No warrantymay be created or extended by sales representatives or written sales materials. The adviceand strategies contained herein may not be suitable for your situation. You should consultwith a professional where appropriate. Neither the publisher nor author shall be liable forany loss of profit or any other commercial damages, including but not limited to special,incidental, consequential, or other damages.

    For general information on our other products and services please contact our CustomerCare Department within the United States at (800) 762-2974, outside the United States at(317) 572-3993 or fax (317) 572-4002.

    Trademarks: Wiley, the Wiley Publishing logo, Audel, and related trade dress are trade-marks or registered trademarks of Wiley in the United States and other countries, and maynot be used without written permission. All other trademarks are the property of theirrespective owners. Wiley Publishing, Inc., is not associated with any product or vendormentioned in this book.

    Wiley also publishes its books in a variety of electronic formats. Some content that appearsin print may not be available in electronic books.

    Library of Congress Cataloging-in-Publication Data: 2003110248

    ISBN: 0-764-54199-4

    Printed in the United States of America

    10 9 8 7 6 5 4 3 2 1

  • Contents

    Introduction vii

    1. Electrical Laws 1

    2. Electronic Components and Circuits 18

    3. Electrical Drawings 33

    4. Motors, Controllers and Circuits 60

    5. Generators 89

    6. Mechanical Power Transmission 104

    7. Electrical Power Distribution 127

    8. Grounding 176

    9. Contactors and Relays 203

    10. Welding 217

    11. Transformers 232

    12. Circuit Wiring 246

    13. Communications Wiring 272

    14. Wiring in Hazardous Locations 296

    15. Tools and Safety 317

    Appendix 330

    Index 336

    v

  • Introduction

    In this handbook for electrical installers you will find a greatnumber of directions and suggestions for electrical installa-tions. These should serve to make your work easier, moreenjoyable, and better.

    But first of all, I want to be sure that every reader of thisbook is exposed to the primary, essential requirements forelectrical installations.

    The use of electricity, especially at common line voltages,is inherently dangerous. When used haphazardly, electricitycan lead to electrocution or fire. This danger is what led tothe development of the National Electrical Code (NEC), andit is what keeps Underwriters Laboratories in business.

    The first real requirement of the NEC is that all workmust be done in a neat and workmanlike manner. Thismeans that the installer must be alert, concerned, and wellinformed. It is critical that you, as the installer of potentiallydangerous equipment, maintain a concern for the peoplewho will be operating the systems you install.

    Because of strict regulations, good training, and fairlygood enforcement, electrical accidents are fairly rare. Butthey do happen, and almost anyone who has been in thisbusiness for some time can remember deadly fires that beganfrom a wiring flaw.

    As the installer, you are responsible for ensuring that thewiring you install in peoples homes and workplaces is safe.Be forewarned that the excuse of I didnt know will notwork for you. If you are not sure that an installation is safe,you have no right to connect it. I am not writing this to scareyou, but I do want you to remember that electricity can kill;it must be installed by experts. If you are not willing toexpend the necessary effort to ensure the safety of yourinstallations, you should look into another trade one inwhich you cannot endanger peoples lives.

    vii

  • viii Introduction

    But the commitment to excellence has its reward. Thepeople in the electrical trade who work like professionalsmake a steady living and are almost never out of work. Theyhave a lifelong trade and are generally well compensated.

    This book is designed to put as much information at yourdisposal as possible. Where appropriate, we have used italicsand other graphic features to help you quickly pick out keyphrases and find the sections you are looking for. In addi-tion, we have included a good index that will also help youfind things rapidly.

    Chapters 1 and 2 of this text cover the basic rules of elec-tricity and electronics. They contain enough detail to helpyou through almost any difficulty that faces you, short ofplaying electronic design engineer. They will also serve youwell as a review text from time to time.

    Chapter 3 explains all common types of electrical draw-ings, their use and interpretation. This should be very usefulon the job site.

    Chapters 4 and 5 cover the complex requirements for theinstallation of motors and generators, and Chapters 6 and 7will guide you in the transmission of both electrical powerand mechanical force.

    Chapter 8 covers the very important safety requirementsfor grounding. The many drawings in this chapter will serveto clarify the requirements for you.

    Chapters 9 through 15 cover a variety of topics, such asthe installation and operation of contactors and relays, weld-ing methods, transformer installations, circuit wiring, com-munications wiring, wiring in hazardous locations, and toolsand safety.

    Following the text of the book, you will find an Appendixcontaining technical information and conversion factors.These also should be of value to you on the job.

    Best wishes,Paul Rosenberg

  • 1. ELECTRICAL LAWS

    An important foundation for all electrical installations is athorough knowledge of the laws that govern the operationof electricity. The general laws are few and simple, and theywill be covered in some depth.

    The multiple and various methods of manipulating elec-trical current with special circuits will not be discussed inthis chapter. A number of them will be covered in Chapter 2.Coverage will be restricted to subjects that pertain to wiringfor electrical construction and to basic electronics. Whilethere are obviously many other things that can be done withelectricity, only those things that pertain to the installers ofcommon electrical systems will be covered.

    The Primary ForcesThe three primary forces in electricity are voltage, currentflow, and resistance. These are the fundamental forces thatcontrol every electrical circuit.

    Voltage is the force that pushes the current through elec-trical circuits. The scientific name for voltage is electromo-tive force. It is represented in formulas with the capital letterE and is measured in volts. The scientific definition of a voltis the electromotive force necessary to force one ampere ofcurrent to flow through a resistance of one ohm.

    In comparing electrical systems to water systems, voltageis comparable to water pressure. The more pressure there is,the faster the water will flow through the system. Likewisewith electricity, the higher the voltage (electrical pressure),the more current will flow through any electrical system.

    Current (which is measured in amperes, or amps forshort) is the rate of flow of electrical current. The scientificdescription for current is intensity of current flow. It is repre-sented in formulas with the capital letter I. The scientific def-inition of an ampere is a flow of 6.25 1023 electrons (calledone coulomb) per second.

    1

  • 2 Electrical Laws

    I compares with the rate of flow in a water system, whichis typically measured in gallons per minute. In simple terms,electricity is thought to be the flow of electrons through aconductor. Therefore, a circuit that has 9 amps flowingthrough it will have three times as many electrons flowingthrough it as does a circuit that has a current of 3 amps.

    Resistance is the resistance to the flow of electricity. It ismeasured in ohms and is represented by the capital of theGreek letter omega (). The plastic covering of a typicalelectrical conductor has a very high resistance, whereas thecopper conductor itself has a very low resistance. The scien-tific definition of an ohm is the amount of resistance thatwill restrict one volt of potential to a current flow of oneampere.

    In the example of the water system, you can compareresistance to the use of a very small pipe or a large pipe. Ifyou have a water pressure on your system of 10 lb per squareinch, for example, you can expect that a large volume ofwater would flow through a six-inch-diameter pipe. A muchsmaller amount of water would flow through a half-inchpipe, however. The half-inch pipe has a much higher resis-tance to the flow of water than does the six-inch pipe.

    Similarly, a circuit with a resistance of 10 ohms (resis-tance is measured in ohms) would let twice as much currentflow as a circuit that has a resistance of 20 ohms. Likewise, acircuit with 4 ohms would allow only half as much currentto flow as a circuit with a resistance of 2 ohms.

    The term resistance is frequently used in a very generalsense. Correctly, it is the direct current (dc) component oftotal resistance. The correct term for total resistance in alter-nating current (ac) circuits is impedance. Like dc resistance,impedance is measured in ohms but is represented by the let-ter Z. Impedance includes not only dc resistance but alsoinductive reactance and capacitive reactance. Both inductivereactance and capacitive reactance are also measured inohms. These will be explained in more detail later in thischapter.

  • Ohms LawFrom the explanations of the three primary electrical forces,you can see that the three forces have a relationship one toanother. (More voltage, more current; less resistance, morecurrent.) These relationships are calculated by using what iscalled Ohms Law.

    Ohms Law states the relationships between voltage, cur-rent, and resistance. The law explains that in a dc circuit,current is directly proportional to voltage and inversely pro-portional to resistance. Accordingly, the amount of voltage isequal to the amount of current multiplied by the amount ofresistance. Ohms Law goes on to say that current is equal tovoltage divided by resistance and that resistance is equal tovoltage divided by current.

    These three formulas are shown in Fig. 1-1, along with adiagram to help you remember Ohms Law. The Ohms Lawcircle can easily be used to obtain all three of these formulas.

    The method is this: Place your finger over the value thatyou want to find (E for voltage, I for current, or R for resis-tance), and the other two values will make up the formula.For example, if you place your finger over the E in the circle,the remainder of the circle will show I R. If you then mul-tiply the current times the resistance, you will get the valuefor voltage in the circuit. If you want to find the value forcurrent, you will put your finger over the I in the circle, andthen the remainder of the circle will show E R. So, to findcurrent, you divide voltage by resistance. Last, if you placeyour finger over the R in the circle, the remaining part of thecircle shows E I. Divide voltage by current to find the valuefor resistance. These formulas set up by Ohms Law apply toany electrical circuit, no matter how simple or how complex.

    If there is one electrical formula to remember, it is cer-tainly Ohms Law. The Ohms Law circle found in Fig. 1-1makes remembering the formula simple.

    Electrical Laws 3

  • 4 Electrical Laws

    Fig. 1-1 Ohms Law diagram and formulas.

    WattsAnother important electrical term is watts. A watt is the unitof electrical power, a measurement of the amount of workperformed. For instance, one horsepower equals 746 watts;one kilowatt (the measurement the power companies use onour bills) equals 1000 watts. The most commonly used for-mula for power (or watts) is voltage times current (E I).

    RE I = RE R = II R = E

    Voltage = Current ResistanceCurrent = Voltage ResistanceResistance = Voltage Current

    Ohm's Law

    IE

  • For example, if a certain circuit has a voltage of 40 voltswith 4 amps of current flowing through the circuit, thewattage of that circuit is 160 watts (40 4).

    Figure 1-2 shows the Watts Law circle for figuringpower, voltage, and current, similar to the Ohms Law circlethat was used to calculate voltage, current, and resistance.For example, if you know that a certain appliance uses 200watts and that it operates on 120 volts, you would find theformula P E and calculate the current that flows throughthe appliance, which in this instance comes to 1.67 amps. Inall, 12 formulas can be formed by combining Ohms Lawand Watts Law. These are shown in Fig. 1-3.

    Fig. 1-2 Watts Law circle.

    IP E = IP I = EI E = P

    EP

    Electrical Laws 5

  • 6 Electrical Laws

    Fig. 1-3 The 12 Watts Law formulas.

    ReactanceReactance is the part of total resistance that appears in alter-nating current circuits only. Like other types of resistance, itis measured in ohms. Reactance is represented by the letter X.

    There are two types of reactance: inductive reactance andcapacitive reactance. Inductive reactance is signified by XL,and capacitive reactance is signified by XC.

    Inductive reactance (inductance) is the resistance to cur-rent flow in an ac circuit due to the effects of inductors in thecircuit. Inductors are coils of wire, especially those that arewound on an iron core. Transformers, motors, and fluores-cent light ballasts are the most common types of inductors.The effect of inductance is to oppose a change in current inthe circuit. Inductance tends to make the current lag behindthe voltage in the circuit. In other words, when the voltagebegins to rise in the circuit, the current does not begin to riseimmediately, but lags behind the voltage a bit. The amountof lag depends on the amount of inductance in the circuit.

    PR

    IE(VOLTS) (AMPS)

    PE

    EI

    PR

    IR

    I 2R

    (OHMS) (WATTS)

    PI

    PI 2

    EI

    PRER

    E 2P

    E 2R

  • The formula for inductive reactance is as follows:

    X FL2L = r

    In this formula, F represents the frequency (measured inhertz) and L represents inductance, measured in henries. Youwill notice that according to this formula, the higher the fre-quency, the greater the inductive reactance. Accordingly,inductive reactance is much more of a problem at high fre-quencies than at the 60 Hz level.

    In many ways, capacitive reactance (capacitance) is theopposite of inductive reactance. It is the resistance to currentflow in an ac circuit due to the effects of capacitors in the cir-cuit. The unit for measuring capacitance is the farad (F).Technically, one farad is the amount of capacitance thatwould allow you to store one coulomb (6.25 1023) of elec-trons under a pressure of one volt. Because the storage ofone coulomb under a pressure of one volt is a tremendousamount of capacitance, the capacitors you commonly use arerated in microfarads (millionths of a farad).

    Capacitance tends to make current lead voltage in a cir-cuit. Note that this is the opposite of inductance, whichtends to make current lag. Capacitors are made of two con-ducting surfaces (generally some type of metal plate or metalfoil) that are just slightly separated from each other (see Fig.1-4). They are not electrically connected. Thus, capacitorscan store electrons but cannot allow them to flow from oneplate to the other.

    In a dc circuit, a capacitor gives almost the same effect asan open circuit. For the first fraction of a second, the capac-itor will store electrons, allowing a small current to flow. Butafter the capacitor is full, no further current can flowbecause the circuit is incomplete. If the same capacitor isused in an ac circuit, though, it will store electrons for partof the first alternation and then release its electrons and storeothers when the current reverses direction. Because of this, acapacitor, even though it physically interrupts a circuit, can

    Electrical Laws 7

  • 8 Electrical Laws

    store enough electrons to keep current moving in the circuit.It acts as a sort of storage buffer in the circuit.

    Fig. 1-4 Capacitor.

    In the following formula for capacitive reactance, F is fre-quency and C is capacitance, measured in farads.

    X FC21

    C = r

    ImpedanceAs explained earlier, impedance is very similar to resistanceat lower frequencies and is measured in ohms. Impedance isthe total resistance in an alternating current circuit. An alter-nating current circuit contains normal resistance but mayalso contain certain other types of resistance called reac-tance, which are found only in ac (alternating current) cir-cuits. This reactance comes mainly from the use of magneticcoils (inductive reactance) and from the use of capacitors(capacitive reactance). The general formula for impedance isas follows:

    ( )R X XZ CL2 2+ -=

    This formula applies to all circuits, but specifically tothose in which dc resistance, capacitance, and inductance arepresent.

    The general formula for impedance when only dc resis-tance and inductance are present is this:

    Z R X L22

    = +

  • The general formula for impedance when only dc resis-tance and capacitance are present is this:

    Z R XC22

    = +

    ResonanceResonance is the condition that occurs when the inductivereactance and capacitive reactance in a circuit are equal.When this happens, the two reactances cancel each other,leaving the circuit with no impedance except for whatever dcresistance exists in the circuit. Thus, very large currents arepossible in resonant circuits.

    Resonance is commonly used for filter circuits or fortuned circuits. By designing a circuit that will be resonant ata certain frequency, only the current of that frequency willflow freely in the circuit. Currents of all other frequencieswill be subjected to much higher impedances and will thusbe greatly reduced or essentially eliminated. This is how aradio receiver can tune in one station at a time. The capaci-tance or inductance is adjusted until the circuit is resonant atthe desired frequency. Thus, the desired frequency flowsthrough the circuit and all others are shunned. Parallel reso-nances occur at the same frequencies and values as do seriesresonances.

    In the following formula for resonances, FR is the fre-quency of resonance, L is inductance measured in henries,and C is capacitance measured in farads.

    FLC2

    1R =

    r

    The simplest circuits are series circuits circuits thathave only one path in which current can flow, as shown inFig. 1-5. Notice that all of the components in this circuit areconnected end-to-end in a series.

    Electrical Laws 9

  • 10 Electrical Laws

    Fig. 1-5 Series circuit.

    Series Circuits

    VoltageThe most important and basic law of series circuits isKirchhoffs Law. It states that the sum of all voltages in aseries circuit equals zero. This means that the voltage of asource will be equal to the total of voltage drops (which areof opposite polarity) in the circuit. In simple and practicalterms, the sum of voltage drops in the circuit will alwaysequal the voltage of the source.

    CurrentThe second law for series circuits is really just commonsense that the current is the same in all parts of the circuit.If the circuit has only one path, what flows through one partwill flow through all parts.

    ResistanceIn series circuits, dc resistances are additive, as shown in Fig.1-6. The formula is this:

    R R R R R RT 1 2 3 4 5= + + + +

    10 V

    2 5

  • Fig. 1-6 dc resistances in a series circuit.

    Capacitive ReactanceTo calculate the value of capacitive reactance for capacitorsconnected in series, use the product-over-sum method (fortwo capacitances only) or the reciprocal-of-the-reciprocalsmethod (for any number of capacitances). The formula forthe product-over-sum method is as follows:

    X X XX X

    T1 2

    1 2#=

    +

    The formula for the reciprocal-of-the-reciprocals methodis this:

    X

    X X X X X1 1 1 1 1

    1T

    1 2 3 4 5

    =+ + + +

    10 V

    RT = 10

    6 4

    Electrical Laws 11

  • 12 Electrical Laws

    Inductive ReactanceIn series circuits, inductive reactance is additive. Thus, in aseries circuit:

    X X X X X XT 1 2 3 4 5= + + + +

    Parallel CircuitsA parallel circuit is one that has more than one path throughwhich current will flow. A typical parallel circuit is shown inFig. 1-7.

    Fig. 1-7 Parallel circuit.

    VoltageIn parallel circuits with only one power source (as shown inFig. 1-7), the voltage is the same in every branch of the circuit.

    20 V

    20 V

    R1 2

    20 V

    R3 4

    20 V

    R2 3

  • CurrentIn parallel circuits, the amperage (level of current flow) inthe branches adds to equal the total current level seen by thepower source. Fig. 1-8 shows this in diagrammatic form.

    Fig. 1-8 Parallel circuit, showing current values.

    ResistanceIn parallel circuits, resistance is calculated by either theproduct-over-sum method (for two resistances):

    R R RR R

    T1 2

    1 2#=

    +

    20 V

    R1

    I 1 = 5 AI 2 = 10 AI 3 = 4 AI T = 19 A

    4

    R3

    5

    R2

    2

    19 A

    5 A

    10 A

    4 A

    Electrical Laws 13

  • 14 Electrical Laws

    Or by the reciprocal-of-the-reciprocals method (for anynumber of resistances):

    R

    R R R R R1 1 1 1 1

    1T

    1 2 3 4 5

    =+ + + +

    Or, if the circuit has only branches with equal resistances:

    number of equal branchesR RBRANCHT '=

    The result of these calculations is that the resistance of aparallel circuit is always less than the resistance of any onebranch.

    Capacitive ReactanceIn series circuits, capacitances are additive. For an example,refer to Fig. 1-9. Notice that each branch has a capacitanceof 100 microfarad (mfd or f, written with the Greekletter mu (), meaning micro). If the circuit has 4 branches,each of 100 mfd, the total capacitance is 400 mfd.

    Inductive ReactanceIn parallel circuits, inductances are calculated by the prod-uct-over-sum or the reciprocal-of-the-reciprocals methods.

    Series-Parallel CircuitsCircuits that combine both series and parallel paths are obvi-ously more complex than either series or parallel circuits. Ingeneral, the rules for series circuits apply to the parts of thesecircuits that are in series; the parallel rules apply to the partsof the circuits that are in parallel.

  • Fig. 1-9 Capacitances in a series circuit.

    A few clarifications follow:

    VoltageAlthough all branches of a parallel circuit are exposed to thesame source voltage, the voltage drops in each branch willalways equal the source voltage (see Fig. 1-10).

    CurrentCurrent is uniform within each series branch, whereas thetotal of all branches equals the total current of the source.

    ResistanceResistance is additive in the series branches, with the total resistance less than that of any one branch.

    C 1

    100 mfd

    C 2

    C 1 = 100 mfdC 2 = 100 mfdC 3 = 100 mfdC 4 = 100 mfdC T = 400 mfd

    100 mfd

    C 3

    100 mfd

    C 4

    100 mfd

    Electrical Laws 15

  • 16 Electrical Laws

    Fig. 1-10 Voltages in a series-parallel circuit.

    Capacitive ReactanceXC is calculated by the reciprocal-of-the-reciprocals methodwithin a series branch, and the total XC of the branches isadditive.

    Inductive ReactanceXL is additive in the series branches, with the total inductivereactance less than that of any one branch.

    Power WiringNearly all power wiring is connected in parallel, so that allloads are exposed to the full line voltage. Loads connected inseries would experience only part of the line voltage.

    One of the most widely used calculations for powerinstallations is simply to calculate amperage when only volt-age and power are known. (See Fig. 1-2 and the associateddiscussion.)

    20 V

    16 V

    4

    4 V

    1

    20 V

    7

  • For power wiring, capacitance is rarely a problem. Oneexception is that long runs of cables can develop a significantlevel of capacitance either between the conductors or betweenone or more of the conductors and a metal conduit encasingthem. A proper grounding system will normally drain such acharge. If, however, there is a flaw in the grounding system,such as a bonding jumper not properly connected, strangevoltages can show up in the system. These voltages are calledphantom voltages.

    Inductance, unlike capacitance, is a serious problem inpower wiring. Inductive reactance causes a difficulty with awiring systems power factor. This will be covered in somedepth in Chapter 7.

    Electrical Laws 17

  • 2. ELECTRONIC COMPONENTS AND CIRCUITS

    The first thing to remember about electronics is that the lawsthat govern the operation of electricity (that is, Ohms Law,Kirchhoffs Law, Watts Law, calculations of parallel resis-tance, etc.) are the same laws that govern electronics. In real-ity, working with electronics is not that different from manytypes of electrical work. The main differences are theamount of power being used and the exotic-sounding namesof electronic components.

    To many people, the names of the devices are especiallyintimidating: Zener diodes, field-effect transistors, PNPjunctions, and so on. When you realize that these are littlemore than fancy names for such things as automaticswitches, a lot of the mystery evaporates. Actually, thesedevices are not especially difficult to understand and use.

    AdvantagesElectronic circuits possess five basic abilities that normalelectrical circuits dont. All of the other amazing abilitiesthat electronic products have are merely combinations ofthese five.

    1. Electronic devices can respond to very small signalsand from them can produce a much larger signal. Thisis how transistors can amplify signals.

    2. Electronic devices can respond much, much fasterthan can electrical devices such as relays.

    3. When operating at high speeds, electronic devices canproduce magnetic signals such as radio waves, X-rays,or microwaves.

    4. Certain types of electronic devices can respond tolight. A good example of this is found in commonphotocells.

    5. Electronic devices can control the direction of currentflow.

    18

  • Tubes and SemiconductorsThe five abilities just mentioned were first evident in vacuumtubes, long before anyone had heard of semiconductors.Without vacuum tubes, radio, TV, X-rays, and a host ofother things would have been impossible. These tubes werethe first electronic devices. They took time to heat up beforethey could operate, they often burnt out, and they were rela-tively expensive. Nevertheless, they could do things that noelectrical device could do, and thus they were very widelyused. Even the first computers were composed of vacuumtubes.

    Semiconductors, however, have gone a step beyond. Firstof all, semiconductors do virtually all of the jobs that elec-tron (vacuum) tubes do, plus a few extra jobs and theyoperate more efficiently. They dont need to warm up beforethey can operate, and they are very small. The first computerfilled up a space the size of a large garage due to the largesize of the tubes. With the small size of semiconductordevices today, you can fit a far, far more powerful computeron a desktop. In the case of the computer, the tubes andsemiconductors primarily did the same jobs, but the size dif-ference was extremely important.

    One more step was critical: developing the means to puthundreds of semiconductors on one small piece of silicon.This device the integrated circuit chip is merely a largenumber of semiconductor devices squeezed into a very smallarea. Needless to say, the IC chip has had a major impact onthe modern world.

    The invention of the electronic tube was crucial to manyof the most important developments of the first half of thetwentieth century; likewise, semiconductors and IC chipswere critical to developments in the last half of the twentiethcentury.

    SemiconductorsIn the electrical field, you are familiar with conductors suchas copper and aluminum wires and buses. There are also

    Electronic Components and Circuits 19

  • 20 Electronic Components and Circuits

    nonconductors (usually called insulators) such as rubber,plastics, and mica. Semiconductors are the materials some-where in between conductors and nonconductors that is,semi-conductors. In other words, they conduct electricitypartially or under certain circumstances.

    If youve ever had an electrical theory class, you willremember that an atom can have a maximum of eight elec-trons in its outer electron shell. You also learned thatbecause electricity is a flow of electrons, atoms with only oneelectron in their outer shell are good conductors because onelone electron can be shaken loose from an atom fairly easily.You also found out that electrons are very hard to removefrom an atom that has seven or eight electrons in its outershell. Therefore, atoms that have seven or eight electrons intheir outer shell are said to be nonconductors.

    Semiconductors are atoms that have four electrons intheir outer shells. These elements are silicon, germanium,and tin. When one element with three electrons in its outershell and another element with five electrons in its outer shellare mixed together, they give the resulting compound anaverage of four outer-shell electrons, making that compounda semiconductor. This is the case with gallium arsenide, acombination of gallium and arsenic.

    Silicon and germanium are the two materials that arecommonly used as semiconductors. But in their pure form,these materials are not very useful. They conduct a little bitof electricity and not much more. It is when you modifythese substances that they become interesting.

    You modify silicon and germanium by adding smallamounts of other materials to them. This is called doping.When properly done, doping gives a semiconductor either asurplus of electrons (making it a type N semiconductor withextra electrons that carry a negative charge) or a deficiencyof electrons (making it a type P semiconductor with a posi-tive bias because of the lack of electrons). You may want to

  • take a moment to review this paragraph to grasp all theimportant details fully.

    Now, the idea of a PN junction is simple: It is merely theplace where type P and type N semiconductors are placedtogether. The idea of an NPN semiconductor is also easy: Itis merely a sandwich with type N layers on the outside and atype P layer in the middle.

    DiodesA diode is simply a PN junction: a piece of type N semicon-ductor joined to a piece of type P semiconductor. (See Fig.2-1.) If you connect a battery to the diode as shown (positiveterminal to N, negative terminal to P), no current will flowthrough the diode with the exception of a very small leak-age current.

    Fig. 2-1 Reverse-biased diode.

    Now, if you look at Fig. 2-2, you see the same diode con-nected the opposite way with the positive terminal to Pand the negative terminal to N. When connected this way,current will flow with very little resistance.

    Figure 2-1 shows the diode connected to the battery in away that makes it reverse-biased. This means that it is con-nected so that it opposes current flow its bias is reversed.

    N P

    +

    Electronic Components and Circuits 21

  • 22 Electronic Components and Circuits

    Fig. 2-2 shows the diode connected to the battery in sucha way as to make it forward-biased. This connection allowsthe current to move forward through it.

    Fig. 2-2 Forward-biased diode.

    Diodes are commonly used to convert alternating currentinto direct current. By simply connecting the diode in serieswith a circuit, you allow current to flow in only one direc-tion; it wont flow in reverse. Thus, the current can no longeralternate; it can flow in only one direction.

    Diodes come in all sizes and ratings. (Make sure youdont connect a diode rated for 24 volts on a 120-volt cir-cuit!) Usually, diodes look like resistors, but they can comein varied sizes and shapes.

    What a Transistor IsAfter you take away all of the mystique surrounding thetransfer resistor, which is what you now call the transistor,you find that it is an automatic switch. Its a pretty impres-sive automatic switch, to be surebut essentially its just anautomatic switch.

    The basic transistor is an NPN junction in which one sideis more heavily doped than the other side. In other words,

    P N

    +

  • one of the N sides is more negative than the other N side.The more heavily doped side is called the emitter, and theless heavily doped side is called the collector. The P sectionthat is sandwiched in between is called the base. This isshown in Fig. 2-3.

    Fig. 2-3 NPN transistor.

    To understand how this device works as an automaticswitch, look now at Fig. 2-4. As shown in this figure, you willconnect the same transistor in a circuit. Looking at the rightside of Fig. 2-4, you see that the collector-to-base NP junctionis reverse-biased. (Refer to Fig. 2-1 again.) Therefore, exceptfor a very small leakage current, no current flows throughthis junction. Now, looking at the left half of Fig. 2-4, you seethat with the switch open no current flows in that part of thecircuit either.

    So far, so good. But when you close the switch, somethingunique happens. As more current flows through the base-to-emitter NP junction (on the left side of Fig. 2-4), it changesthe charges in the other NP junction and allows current toflow through it, too. If current flows in the left side of thecircuit (base-to-emitter), current will flow through the rightside also (collector-to-emitter). If no current flows in the left(base-to-emitter) side, none will flow in the right (collector-to-emitter) side either.

    N NP

    Base

    Emitter Collector

    Electronic Components and Circuits 23

  • 24 Electronic Components and Circuits

    Fig. 2-4 NPN transistor connected in a circuit.

    The scientific explanation of why and how the second NPjunction changes to allow current to flow is a difficult one.For this book, let it be sufficient to accept the fact that itdoes work.

    If you look at Fig. 2-4 again, you see that the voltage ofthe battery supplying power on the left side of the diagram isonly 1 volt, but the voltage on the right side is 20 volts. So,with this circuit, you can use a 1-volt circuit to control a 20-volt circuit. This is a basic amplifier.

    Now, to make it really interesting, here is one last thingthat the transistor does: It keeps the current that flowsthrough the right side of our circuit proportional to the cur-rent level in the left side of the circuit. In other words, if 5milliamps flow through the left side, allowing 100 milliampsto flow through the right side, then increasing the current inthe left side to 10 milliamps will automatically increase thecurrent in the right side to 200 milliamps. (You are assuming

    + +

    N NP

    20 V

    Base

    1 V

    Emitter Collector

  • here that all other things remain unchanged.) This relation-ship is shown in Fig. 2-5.

    Fig. 2-5 Current relationships in transistor circuit.

    You can see from this description how useful transistorsare. And considering that they can be produced in extremelysmall sizes, they become much more important.

    Silicon-Controlled RectifiersThese devices, which are usually called SCRs, are composedof four layers of silicon P and N semiconductors (see Fig.2-6). Unless current is put through the gate lead of thedevice, no current will flow from the anode to the cathode. Ifthere is a gate current, the resistance between the anode andthe cathode drops to almost zero, allowing current to flowfreely. Thus, the gate current is necessary to start the rest ofthe SCR conducting. Unlike the transistor, however, the cur-rent will continue to flow from the anode to the cathode,even when the gate current ceases. Once started, the anode-to-cathode current will flow until it stops on its own; itwont be stopped by the SCR.

    SCRs are particularly useful because they can handlelarge amounts of current, especially as compared to othersolid-state devices. Commonly available SCRs can handlecontinuous currents of hundreds of amps.

    Cur

    rent

    Time

    C - to - B

    B - to - E

    Electronic Components and Circuits 25

  • 26 Electronic Components and Circuits

    Fig. 2-6 Silicon-controlled rectifier.

    TriacsTriacs are modified SCRs, as shown in Fig. 2-7. The triacblocks current flow in either direction until a current is sentin or out of its gate. Once one of these currents begins, cur-rent will be allowed to flow in either direction through thetriac.

    Triacs are the functional components inside most dimmerswitches and similar devices.

    Field-Effect TransistorsField-effect transistors use type P semiconductors on bothsides of a type N semiconductor to act as a gate. The P semi-conductor gate controls current flowing through the type Nsemiconductor.

    P

    ANODE

    NPN

    CATHODE

    GATE

  • Fig. 2-7 Triac.

    Figure 2-8 shows a field-effect transistor. In this transis-tor, the type N semiconductor will carry the current that youwant to control. If you place a voltage on the type P semi-conductor (the gate), no current will be allowed to flowthrough the type N semiconductor. The voltage placed onthe P sections creates an electrostatic field that alters thecharges in the type N semiconductor, disallowing the passageof current. When the voltage on the P sections is eliminatedor reduced, current will be able to pass from the source tothe drain of the field-effect transistor.

    P

    T2

    N

    N

    N

    PNN

    HEAT SINK

    GATE T1

    Electronic Components and Circuits 27

  • 28 Electronic Components and Circuits

    Fig. 2-8 Field-effect transistor.

    Zener DiodesThe Zener diode is a PN diode that has been specially doped.Zener diodes are usually connected in circuits in the reverse-biased position and are used as surge protectors. Typically,they are installed parallel with a load that is to be protected,in the same manner as a lightning arrestor.

    Connected in this way, Zener diodes oppose current flow(the definition of reverse-biased). But when the voltageapplied to them reaches a certain level, called the breakdownvoltage, they will conduct a current easily. This has the effectof shunting the voltage away from the load being protectedand sending it through the Zener diode instead.

    When properly sized Zener diodes are used this way, theyprovide a high level of overcurrent protection for sensitivecircuits. They are especially useful because they have a veryfast response time. The Zener diode will respond to an over-voltage within a few nanoseconds, rather than taking themany milliseconds of response time required by other typesof surge suppressors before they can protect the circuit.

    Working with Electronic ComponentsThe basic rules of working with electrical components applyalso to electronic devices: Handle with care, and make surethat you use parts at or below their rated voltage and wattage.

    Most electronic parts are very durable and thus not oftendamaged by normal treatment. Nevertheless, you may want

    P

    N

    PSOURCE DRAIN

  • to pay a little extra attention to the temperatures at whichthey are stored or operated. High temperatures can have adeteriorating effect on certain electronic items. Also bewareof installing parts with pins. Take care not to bend the pins;insert them straight into their places and dont twist or turnthem. They simply cant take the stress.

    Voltage and wattage ratings are critical. You must keepall items within their limits. Failure to do so will usuallyresult in an instant problem. Although electronic parts canbe extremely effective, they are not at all forgiving. They willpromptly blow out if you apply them incorrectly.

    If you are going to work with electronics, you will need tomaster one mechanical skill soldering.

    Fortunately, soldering is quite easy to do; you merelyneed to spend some time practicing. Get a good grade of sol-dering iron (properly called a soldering pencil), somerosin-core solder, and an old circuit board to practice on.The soldering pencil should be rated between 25 and 40watts for electronics work. Too much wattage results in toomuch heat, which can damage some items. We wont takethe space here to go through all the details of soldering. Agood soldering iron should come with soldering instructions.Sorry, there are no shortcuts. You simply must practice untilyou have a good feel for what you are doing.

    You may also want to get a desoldering tool. Desolderingtools are often necessary for removing components from cir-cuit boards. As with the soldering iron, practice until you getit right.

    Printed Circuit BoardsThere are two main concerns when working with printedcircuit boards. The first is that you install and remove themproperly. They should always be inserted and/or removedwith an end-to-end motion rather than with a side-to-sidemotion. See Fig. 2-9.

    Electronic Components and Circuits 29

  • 30 Electronic Components and Circuits

    Fig. 2-9 Proper method of removing circuit boards.

    The second concern with circuit boards is handlingrepairs or replacements. Because of their complexity, manyof the components on these boards are nearly impossible totroubleshoot. In addition, manufacturers generally replacethe entire board if you return it to them. But once a boardhas been worked on, the manufacturer has no way ofknowing if the board was damaged because of a manufac-turing error or because of your work on it. In these cases,manufacturers dont replace the board without payment.Call the manufacturer before you tamper with its boards,especially if they are still under warranty. Treat theseboards with care; they are often worth hundreds or thou-sands of dollars.

    Electronic InstallationsElectronic systems require more preplanning than regularelectrical systems. For an electrical project, you can grab sev-eral boxes of switches and receptacles and just wire them up.For electronic installations, you must know exactly whereevery item is supposed to go. These items are not mix andmatch. In most electrical installations, no one will ever

    DON'T USE THIS MOTION

    USETHIS

    MOTION

  • know or care if you use Hubbel wiring devices on one side ofthe building and Leviton on the other. But if you try mixingmanufacturers in electronics, your chances are very slim thatthe system will work well. And even if it does, the manufac-turers are often free of their warranty obligations if they findthat you mixed brands of equipment.

    This means extra planning is needed before the jobbegins. It also means that you need better working drawingsand that installers need to pay more attention to details. Youmust use the exact devices and exact cable types designed forthe installation. These systems can do amazing things, butthey must be installed according to precise designs.

    Also different from electrical installations is the wayproblems are solved. Everyone wants to solve problems witha minimum of hassle, but you must use extra caution in solv-ing electronic problems. Unless you understand the system aswell as the designer does, call the designer rather than flyingon your own. If you dont, you could very easily fix theproblem you are immediately concerned with but inadver-tently create a larger problem in the process. All of the sys-tems components must operate together; changing one piececan often affect several others.

    Remember that you will probably have to spend sometime fixing bugs in a complex system. Unless you are veryfamiliar with a certain system, budget some extra time to fixsmall problems after the system becomes operational.

    TestingPlan on testing your electronic systems periodically as yourwork progresses. Again, this procedure is different from thatused with regular electrical work, which is sometimes testedonly just before the power is turned on, after the installationis complete.

    Depending on what type of system you are installing, youmay want to test several parts of the system before you evenget close to turning it on.

    Electronic Components and Circuits 31

  • 32 Electronic Components and Circuits

    With power or lighting circuits, the worst that can nor-mally happen if you make a mistake is that a circuit breakerwill snap at you. But with electronic systems, you can easilyburn out thousands of dollars worth of equipment.

    These cautions are especially pertinent to electricians wholearned power wiring carefully, but who are just beginningto understand electronic components and are doing so withlittle or no formal training. Proceed carefully, and dont takerisks you dont completely understand. Err on the side ofcaution.

  • 3. ELECTRICAL DRAWINGS

    The construction documents supplied for a new building(normally by an architectural or engineering firm) include allarchitectural drawings that show the design and buildingconstruction details. These include floor plan layouts, verti-cal elevations of all building exteriors, various cross sectionsof the building, and other details of construction. Whilethere may be a number of such drawings, they fall into fivegeneral groups:

    1. Site plans. These plans include the location of thebuilding and show the location and routing of all out-side utilities (water, gas, electricity, sewer, etc.) thatwill serve the building, as well as other points of usagewithin established property lines. Topography linesare sometimes included with site plans, especiallywhen the building site is on a slope.

    2. Architectural. These drawings include elevations of allexterior faces of the building; floor plans showingwalls, doors, windows, and partitions on each floor;and sufficient crosssections to clearly indicate variousfloor levels and details of the foundation, walls, floors,ceilings, and roof construction. Large-scale detaildrawings may also be included.

    3. Structural. Structural drawings are included for reinforced-concrete and structural-steel buildings.Structural engineers prepare these drawings.

    4. Mechanical. The mechanical drawings cover the com-plete design and layout of the plumbing, piping, heat-ing, ventilating, and air conditioning systems andrelated mechanical construction. Electrical controlwiring diagrams for the heating and cooling systemsare often included on the mechanical drawings as well.

    33

  • 34 Electrical Drawings

    5. Electrical. The electrical drawings cover the completedesign and layout of the electrical wiring for lighting,power, signals and communications, special electricalsystems, and related electrical work. These drawingssometimes include a site plan showing the location ofthe building (on the property) and the interconnectingelectrical systems. They can also include floor plansshowing the location of power outlets, lighting fix-tures, panelboards, power-riser diagrams, and larger-scale details where necessary.

    In order to read any of these drawings, you need tobecome familiar with the meanings of the many symbols,lines, and abbreviations used.

    Plan SymbolsBecause electrical drawings must be prepared by electricaldraftsmen quickly and within budget, symbols are used tosimplify the work. Therefore, anyone who must interpretand work with the drawings must have a solid knowledge ofelectrical symbols.

    Most engineers and designers use electrical symbolsadopted by the American National Standards Institute(ANSI). Many of these symbols, however, are frequently mod-ified to suit a specific need for which there is no standard sym-bol. For this reason, most drawings include a symbol list orlegend as part of the drawings or in the written specifications.

    A listing of the most common types of plan symbols isshown in Table 3-1. This list represents a good set of electri-cal symbols in that they are (1) easily drawn by draftsmen,(2) easily interpreted by workmen, and (3) sufficient formost applications.

    It is evident from Table 3-1 that many symbols have thesame basic form, but their meanings differ slightly with theaddition of a line, mark, or abbreviation. Therefore, a goodprocedure to follow in learning the different electrical sym-bols is first to understand the basic forms and then to applythe variations of that form to obtain the different meanings.

  • Table 3-1 Plan Symbols

    Receptacle Outletsa

    Single receptacle outlet.

    Duplex receptacle outlet.

    Triplex receptacle outlet.

    Quadruplex receptacle outlet.

    Duplex receptacle outletsplit wired.

    Triplex receptacle outletsplit wired.

    Single special-purpose receptacle outleta.

    Duplex special-purpose receptacle outleta.

    Range outlet.

    Special-purpose connection or provisionfor connection. Use subscript letters toindicate function (DWdishwasher;CDclothes dryer, etc.).

    Multioutlet assembly. Extend arrows tolimit of installation. Use appropriatesymbol to indicate type of outlet. Alsoindicate spacing of outlets as x inches.

    Clock hanger receptacle.

    Fan hanger receptacle.

    Floor single receptacle outlet.

    (continued)

    F

    C

    X"

    DW

    R

    Electrical Drawings 35

  • 36 Electrical Drawings

    Table 3-1 (continued)

    Receptacle Outletsa

    Floor duplex receptacle outlet.

    Floor special-purpose outleta.

    Floor telephone outletpublic.

    Floor telephone outletprivate.

    Switch Outlets

    S Single-pole switch.

    S2 Double-pole switch.

    S3 Three-way switch.

    S4 Four-way switch.

    SK Key-operated switch.

    SP Switch and pilot lamp.

    SL Switch for low-voltage switching system.

    SLM Master switch for low-voltage switchingsystem.

    Switch and single receptacle.

    Switch and double receptacle.

    SD Door switch.

    ST Time switch.

    SCB Circuit-breaker switch.

    SMC Momentary contact switch or push-button for other than signaling system.

    S

    S

  • Circuitingc

    Wiring concealed in ceiling or wall.

    Wiring concealed in floor.

    Wiring exposed.

    Note: Use heavyweight line to identifyservice and feeders. Indicate emptyconduit by notation CO (conduit only).

    3 wires Branch-circuit home run to panelboard.Number of arrows indicates number ofcircuits. (A numeral at each arrow maybe used to identify circuit number.) Note: Any circuit without furtheridentification indicates two-wire circuit.For a greater number of wires, indicatewith cross lines.

    4 wires, etc. Unless indicated otherwise, the wire size of the circuit is the minimum sizerequired by the specification.

    Identify different functions of wiringsystemfor example, signaling system bynotation or other means.

    Wiring turned up.

    Wiring turned down.

    Lighting Outlets

    Ceiling Wall

    Surface or pendant incandescent,mercury vapor, or similar lamp fixture.

    Recessed incandescent, mercury vapor, orsimilar lamp fixture.

    (continued)

    R R

    2 1

    Electrical Drawings 37

  • 38 Electrical Drawings

    Table 3-1 (continued)

    Lighting Outlets

    Ceiling Wall

    Surface or pendant individual fluorescentfixture.

    Recessed individual fluorescent fixture.

    Surface or pendant continuous-rowfluorescent fixture.

    Recessed continuous-row fluorescentfixturea.

    Bare-lamp fluorescent stripb.

    Surface or pendant exit light.

    Recessed exit light.

    Blanked outlet.

    Junction box.

    Outlet controlled by low-voltageswitching when relay is installed in outlet box.

    Panelboards, Switchboards, and Related Equipment

    Flush-mounted panelboard and cabineta.

    Surface-mounted panelboard andcabineta.

    Switchboard, power control center, unitsubstationsa should be drawn to scale.

    Flush-mounted terminal cabinet.a Insmall-scale drawings the TC may beindicated alongside the symbol.

    Surface-mounted terminal cabinet.a Insmall-scale drawings the TC may beindicated alongside the symbol.

    TC

    TC

    L L

    J J

    B B

    XR XR

    X X

    OR

    O

    OR

    O

  • Panelboards, Switchboards, and Related Equipment

    Pull box (identify in relation to wiringsection and sizes).

    Motor or other power controllera.

    Externally operated disconnectionswitcha.

    Combination controller and disconnection meansa.

    aUnless noted to the contrary, it should be assumed that every receptacle will begrounded and will have a separate grounding contact.bUse the uppercase subscript letters described under Section 2 item a-2 of this Standardwhen weatherproof, explosion-proof, or some other specific type of device will be required.

    Note also that some of the symbols listed contain abbre-viations, such as WP for weatherproof and S for switch.Others are simplified pictographs, such as the symbols for asafety switch or panelboard. In other cases, the symbols arecombinations of abbreviations and pictographs, such as thesymbol for nonfusible safety switches.

    Types of Electrical DrawingsThe most common types of electrical drawings are these:

    1. Electrical construction drawings2. Single-line block diagrams3. Schematic wiring diagrams

    Electrical construction drawings show the physicalarrangement and views of specific electrical equipment.These drawings give all the plan views, elevation views, andother details necessary to construct the installation. Forexample, Fig. 3-1 shows a pictorial sketch of a wire trough(auxiliary gutter). One side of the trough is labeled top,one is labeled front, and another is labeled end.

    Electrical Drawings 39

  • 40 Electrical Drawings

    Fig. 3-1 Pictorial sketch.

    This same trough is represented in another form in Fig.3-2. The drawing labeled top is what one sees when view-ing the panelboard directly from above; the one labeledend is viewed from the side; and the drawing labeledfront shows the panelboard when viewing the paneldirectly from the front.

    Fig. 3-2 Top, front, and side views.

    The width of the trough is shown by the horizontal linesof the top view and the horizontal lines of the front view.The height is shown by the vertical lines of both the front

    TOP

    FRONT

    INCHES

    RIGHTSIDE

    LEFTSIDE

    0 3 6 9 12

    RIGHTEND

    LEFTEND

    TOP

    FRONT

  • and the end views, while the depth is shown by the verticallines of the top views and the horizontal lines of the sideview.

    The three drawings in Fig. 3-2 clearly give the shape ofthe wire trough, but the drawings alone would not enable aworker to construct it, because there is no indication of thesize of the trough. There are two common methods to indi-cate the actual length, width, and height of the wire trough.The first is to draw all of the fields to some given scale, suchas 112 in. = 1ft 0 in. This means that 112 in. on the drawingrepresents 1 ft in the actual construction. The secondmethod is to give dimensions on the drawings like the oneshown in Fig. 3-3. Note that the gauge and type of materialare also given in this drawing; there is enough data to showclearly how the panelboard is to be constructed.

    Fig. 3-3 Alternate-method top, front, side views.

    Electrical construction drawings like the ones justdescribed are used mainly by electrical equipment manufac-turers. The electrical installer will more often run acrosselectrical construction drawings like the one shown in Fig.3-4. This type of construction drawing is normally used tosupplement a buildings electrical system drawings for a spe-cial installation and is often referred to as an electrical detaildrawing.

    TOP

    6

    FRONTLEFTEND

    RIGHTEND

    6

    64 0

    Electrical Drawings 41

  • 42 Electrical Drawings

    Electrical diagrams intend to show, in diagrammaticform, electrical components and their related connections. Indiagrams, electrical symbols are used extensively to repre-sent the various components. Lines are used to connect thesesymbols, indicating the size, type, and number of wires thatare necessary to complete the electrical circuit.

    The electrical contractor will often come into contactwith single-line block diagrams. These diagrams are usedextensively to indicate the arrangement of electrical serviceson electrical working drawings. The power-riser diagram inFig. 3-5 is typical of such drawings. It shows the panelboardand all related equipment, as well as the connecting linesthat indicate the circuits and feeders. Notes are used to iden-tify each piece of equipment and to indicate the size of con-duit necessary for each circuit or feeder, as well as thenumber, size, and type of insulation on the conductors ineach conduit.

    Fig. 3-4 Perspective drawing.

    1

    1

    3/4

  • Fig. 3-5 Power-riser diagram.

    A schematic wiring diagram, as shown in Fig. 3-6, is sim-ilar to a single-line block diagram except that the schematicdiagram gives more detailed information and shows theactual size and number of wires used for the electrical connections.

    Anyone involved in the electrical construction industry, inany capacity, frequently encounters all three types of electri-cal drawings. Therefore, it is important for everyone involvedin this industry to fully understand electrical drawings, wiringdiagrams, and other supplementary information found inworking drawings and in written specifications.

    ELECTRIC PANELSEE SCHEDULE

    3 4/0 AI CONDUCTORSIN 2.1/2" CONDUIT

    TIME CLOCKTO CONTROLOUTSIDE LIGHTS

    NO. 4 BARE COPPERTO COLD WATER PIPE

    TC

    PANELA

    Electrical Drawings 43

  • 44 Electrical Drawings

    Fig. 3-6 Schematic wiring diagram.

    Wiring DiagramsComplete schematic wiring diagrams are used infrequently onthe average set of electrical working drawings (only for com-plicated systems such as control circuits), but it is important to

    L1 L1 T11M

    NO.1COMPRESSOR

    1-0.L.

    L2

    L3 L3 T3

    L2 T2

    L1 T1

    NO.3COMPRESSOR

    3-0.L.

    L3 T3

    L2 T2

    L1 L1 T13M

    4M

    2M

    0.L.

    440/480 OR 550 V

    220 V 5M RESET

    2 AMP FUSE2 AMP FUSE

    3TC

    2H1TC

    2TC

    F.S.

    NO.4COMPRESSOR

    1-0.L.

    L2

    L3 L3 T3

    L2 T2

    L1 T1NO.2 COMPRESSOR

    BLOWER MOTOR

    2-0.L.

    5M

    L1 T1L1

    L3 T3

    L2 T2

    L2 T2L2

    L3 T3L3

    8

    6

    5M3

    4

    2

    1

    3

    W

    B

    G

    R

    57

    4M

    2M

    3M

    1M

    C.S.

    4H

    3TDR

    1TDR

    2TDR1H

    3H

    P

    P

    P

    P

    "X" SEE NOTE

    "X" SEE NOTE1TDR

    2TDR

    3TDR

    "X" SEE NOTE

  • have a thorough understanding of them when the need tointerpret them arises.

    Components in schematic wiring diagrams are representedby symbols, and every wire is shown either by itself orincluded in an assembly of several wires that appear as oneline on the drawing. Each wire in the assembly is numberedwhen it enters, however, and it keeps the same number whenit emerges to be connected to some electrical component in thesystem. Fig. 3-7 shows a complete schematic wiring diagramfor a three-phase ac magnetic motor starter. Note that this dia-gram shows the various devices (in symbol form) and indi-cates the actual connections of all wires between the devices.

    Fig. 3-7 Schematic wiring diagram for magnetic motor starter.

    Fig. 3-8 gives a list of electrical wiring symbols commonlyused for single-line schematic diagrams. Single-line diagramsare simplified versions of complete schematic diagrams. Fig.3-9 shows the use of these symbols in a typical single-linediagram of an industrial power-distribution system.

    START

    STOP

    3

    21

    T2

    MOTOR

    M

    L2L1 L3

    T3T1

    Electrical Drawings 45

  • 46 Electrical Drawings

    Fig. 3-8 Symbols used for single-line schematics.

    ELECTRIC MOTOR (HP AS INDICATED)

    POWER TRANSFORMER

    POTHEAD (CABLE TERMINATION)

    CIRCUIT ELEMENT,E.G., CIRCUIT BREAKER

    CIRCUIT BREAKER

    FUSIBLE ELEMENT

    SINGLE-THROW KNIFE SWITCH

    DOUBLE-THROW KNIFE SWITCH

    GROUND

    BATTERY

    CONTACTOR

    PHOTOELECTRIC CELL

    VOLTAGE CYCLES, PHASE

    RELAY

    EQUIPMENT CONNECTION (AS NOTED)

    1 4

    C

    EX: 480/60/3

    PE

    R

    CB

  • Fig. 3-9 Diagram of industrial power-distribution system.

    Power-riser diagrams are probably the most frequentlyencountered diagrams on electrical working drawings forbuilding construction. Such diagrams give a picture of whatcomponents are to be used and how they are to be connectedin relation to one another. This type of diagram is more easily understood at a glance than diagrams previously

    4160/2400V

    120/208V

    AIR CIRCUIT BKRS.ELEC. INTERLOCKEDAUTOMATIC TRANSFER

    FURNISHED ANDINSTALLED BYOWNER

    TIE BREAKER 3O, 4W, 120/208V

    FURNISHED ANDINSTALLED BY THE

    POWER CO.NC

    KI

    KI

    KI

    NC NO

    Electrical Drawings 47

  • 48 Electrical Drawings

    described. As an example, compare the power-riser diagramin Fig. 3-10 with the schematic diagram in Fig. 3-11. Bothare wiring diagrams of the same electrical system, but it iseasy to see that the drawing in Fig. 3-10 is greatly simplified,even though a supplemental schedule is required to give allnecessary data for constructing the system. Such diagramsare also frequently used on telephone, television, alarms, andsimilar systems.

    Fig. 3-10 Power-riser diagram.

    Site PlansA site plan is a plan view that shows the entire property, withthe buildings drawn in their proper locations on the plot.Such plans sometimes include sidewalks, driveways, streets,and utility systems related to the building or project.

    4 - 3/0 THW CONDUCTORSIN 2 1/2 CONDUIT

    MPANEL

    A

  • Site plans are drawn to scale using the engineers scalerather than the architects scale used for most building plans.On small lots, a scale of 1 in. = 10 ft or 1 in. = 20 ft is com-monly used. This means that 1 in. (actual measurement onthe drawing) is equal to 10 ft or 20 ft on the land itself.

    Fig. 3-11 Schematic diagram of the same system as Fig. 3-10.

    4-3/0 THWCONDUCTORS

    IN 2 1/2 C

    20A20A20A20A

    TO LOADS

    200A

    20A20A20A

    Electrical Drawings 49

  • 50 Electrical Drawings

    In general building construction practice, it is the ownersresponsibility to furnish the architect with property andtopographic surveys made by a certified land surveyor orcivil engineer. These surveys will show (1) all property lines,(2) existing utilities and their location on or near the prop-erty, (3) the direction of the land slope, and (4) the conditionof the land (rocky, wet, or whatever).

    The site plan is used to incorporate all new utilities. Theelectrical installer will then be concerned with the electricaldistribution lines, the telephone lines, and the cable televi-sion lines, especially if they are to be installed underground.

    Layout of Electrical DrawingsThe ideal electrical drawing should show in a clear, concisemanner exactly what is required of the installer. The amountof data shown on such drawings should be sufficient, but notoverdone. Unfortunately, this is not always the case. Thequality of electrical drawings varies widely.

    In general, a good set of electrical drawings should con-tain floor plans for each floor of the building (assuming thatthe project is a building), including one plan for lighting cir-cuitry and one plan for power circuitry; riser diagrams toshow the service equipment, feeders, and communicationequipment diagrammatically; schedules to indicate the com-ponents of the service equipment, lighting fixtures, and simi-lar equipment; and large-scale detailed drawings for specialor unusual portions of the installation. A legend or electricalsymbol list should also be provided on the drawings in orderto explain the meaning of every symbol, line, and notationused on the drawings. Anything that cant be explained bysymbols and lines should be clarified with neatly lettered notesor explained in the written specifications. The scale to whichthe drawings are prepared is also important. Drawings shouldbe as large as practical, and where dimensions need to beextremely accurate, dimension lines should be added. Fig. 3-12shows a poorly prepared electrical drawing, whereas Fig. 3-13

  • shows one of relatively good quality. In Fig. 3-12 it is obviousthat the electrical contractor will have to lay out or design por-tions of the system before it can be properly installed.

    Fig. 3-12 Low-quality electrical drawings.

    FEET

    02

    4

    Electrical Drawings 51

  • 52 Electrical Drawings

    The following steps are necessary in preparing a good setof electrical working drawings and specifications:

    1. The engineer or electrical designer meets with thearchitect and the owner to discuss the electrical needsof the building in question and also to discuss variousrecommendations made by all parties.

    2. Once the data in the first step is agreed upon, an out-line of the architects floor plan is drawn on tracingpaper and then several prints of this floor plan outlineare made.

    3. The designer or engineer then calculates the powerand lighting requirements for the building andsketches them on the prints.

    4. All communication and alarm systems are located onthe floor plans, along with lighting and power panel-boards. These are sketched on the prints as well.

    5. Circuit calculations are made to determine wire sizeand overcurrent protection and are then reflected onthe drawings.

    6. After all the electrical loads in the entire building havebeen determined, the main electric service and relatedcomponents (transformers, etc.) are selected andsketched on the prints.

    7. Schedules are next in line to identify various pieces ofelectrical equipment.

    8. Wiring diagrams are made to show the workers howvarious electrical components are to be connected. Anelectrical symbol list is also included to identify thesymbols used on the drawings.

    9. Various large-scale electrical details are included, if nec-essary, to show exactly what is required of the workers.

    10. Written specifications are then made to give a descrip-tion of the materials and the installation methods.

  • Fig. 3-13 Good-quality electrical drawings.

    ALL

    1A

    LL1

    ALL

    1

    4

    4

    3

    2

    2

    AL L

    1

    MD

    PE

    EXIS

    TIN

    G 8

    00A

    MA

    IND

    IST

    RIB

    UT

    ION

    PAN

    EL

    WA

    SH R

    OO

    M F

    LOO

    R P

    LAN

    1/8

    = 1

    0

    E

    AA

    AL L

    1

    AL L

    1

    3

    ALL

    1

    AL L

    1

    2

    Electrical Drawings 53

  • 54 Electrical Drawings

    If these steps are properly taken in preparing a set of elec-trical working drawings, the drawings will be sufficientlydetailed and accurate to enable a more rapid installation.

    SchedulesA schedule, as related to electrical drawings, is a systematicmethod of presenting notes or lists of equipment on a draw-ing, in tabular form. When properly organized and thor-oughly understood, schedules not only are powerful,time-saving methods for the draftsmen, but they also savethe electrical personnel much valuable time in installing theequipment in the field.

    For example, the lighting fixture schedule in Fig. 3-14lists the fixture type corresponding to letters or numbers onthe drawings. The manufacturer and catalog number of eachfixture are included, along with the number, size, and type oflamp for each. The Volts and Mounting columns follow, andthe column on the extreme right is for special remarks suchas the mounting height for a wall-mounted fixture.

    Sometimes schedules are omitted from the drawings, andthe information is placed in the written specificationsinstead. This is not a good practice. Combing through pageafter page of written specifications is time-consuming.Furthermore, workers dont always have access to the speci-fications while working, whereas they usually do have accessto the working drawings at all times.

    The schedules in Figs. 3-15 through 3-17 are typical ofthose used by consulting engineers on electrical drawings.

  • Fig. 3-14 Lighting fixture schedule.

    Fig. 3-15 Intercom schedule.

    FRANK J. SULLIVAN ASSOCIATESCONSULTING ENGINEERSWASHINGTON 36, D.C.

    PROJECT:

    INTERCOMMUNICATION SYSTEM SCHEDULE

    DATE:

    JOB: BY:

    ITEM 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 REMARKSROOMNAMEI.D.NO.

    1

    234

    56

    7

    21

    2019

    1817

    1615

    222324

    2526

    LIGHTING FIXTURE SCHEDULE

    MANUFACTURER'S DESCRIPTION REMARKSMOUNTINGVOLTSLAMPS

    TYPENO.FIXT.TYPE

    Electrical Drawings 55

  • 56 Electrical Drawings

    Fig. 3-16 Load center schedule.

    Fig. 3-17 Motor control schedule.

    Sectional ViewsSometimes the construction of a building is difficult to showwith the regular projection views normally used on electricaldrawings. For example, if too many broken lines are needed

    DATEBY

    PROJECT/JOB NO.

    REMCONTROLDEVICES

    POWERCONTROLDIAGRAM

    AUX EQUIP NAMEPLATEDESIGNATION

    REMARKS

    _ _ MCC _ _

    FUSESIZE

    SWSIZE

    P'SSTR.SIZE

    FLAHPKW

    ITEMNO

    MAINS A.MOTOR CONTROL CENTER NO. MCC O V.

    LOAD CENTER UNIT SUBSTATION EQUIPMENT SCHEDULE

    DESIGNATIONEQUIPMENTSWITCH

    POLES FUSERATINGSWITCHRATING

    ITEM

  • to show hidden objects in buildings or equipment, the draw-ings become confusing and difficult to read. Therefore, inmost cases building sections are shown on working draw-ings, to clarify the construction. To better understand abuilding section, imagine that the building has been cut intosections with a saw. The floor plan of a building in Fig. 3-18shows a sectional cut at point A-A. This sectional view isthen shown in Fig. 3-19.

    Fig. 3-18 Floor plan showing cut at A-A.

    CORRIDOR

    D.H. WNDW.

    MENWOMEN

    TABLES

    STORAGE ROOM

    SHELVES

    A8 1 4

    11 4

    1 5

    4 4

    0

    5 4

    2 0

    26

    8

    1 4

    3 0

    4

    4

    4 8

    8

    6

    5 5 5 5

    8

    A

    4

    Electrical Drawings 57

  • 58 Electrical Drawings

    Fig. 3-19 Sectional view of cut shown in Fig. 3-18.

    2 PLYWOOD

    2 x 8 WD. PLATE

    1/2 0 x 6 LONGANCHOR BOLT AT4 x 0 O.C.

    2 x 4 OUTRIGGERS

    8 C.M.U.

    14

    11

    1 /2

    EXPANSION JT.

    4 CONC. SLAB

    FIN. GRADE

    12 C.M.U. BEYOND

    1/2 PLYWOOD

    1/2 PLYWOOD

    PRE-FAB WOOD TRUSSW/2 x 6 TOP AND BOTTOM CHORDS

    3 0

    CONC. FOOTING

    CONC. FOOTINGBEYOND FOR 12WALL.

    NOTE: FOOTING TO BE ONSOLID GROUND BELOWFROST LINE.

    WALL SECTION

    4 STONE6

    4

    1 0

    VAR

    IES

  • Fig. 3-20 Cutting-plane line.

    In dealing with sections, it is important to use a consider-able amount of visualization. Some sections are very easy toread and others are extremely difficult, because there are noset rules for determining what a section will look like. Forexample, a piece of rigid conduit, cut vertically, will have theshape of a rectangle; cut horizontally, it will have a round orcircular appearance; but on the slant, it will be an ellipse.

    A cutting-plane line (Fig. 3-20) has arrowheads to show thedirection in which the section is viewed. Letters such as A-A orB-B are normally used with the cutting-plane lines to identifythe cutting plane and the corresponding sectional views.

    Electrical Drawings 59

  • 4. MOTORS, CONTROLLERS, AND CIRCUITS

    Motors are among the most commonly used electricaldevices. They vary in size, from specially designed medicalmotors that are less than an inch long to gigantic industrialunits of several thousand horsepower. In between are liter-ally hundreds of different types of motors for thousands ofdifferent applications. Therefore, it is very important for theelectrical installer to understand the rules regarding theapplication and wiring of motors. Generally, the concernscan be broken down into four categories:

    1. Mechanical safety. You must ensure that the motorsthemselves dont constitute a source of danger. Forinstance, you must take care not to install openmotors in areas where they attract curious children toinvestigate and injure themselves. Likewise, it is oftena good idea to put a clutch on a motor to avoid possi-ble injury to the machine operator.

    2. Mechanical stability and operations. Motors have anumber of mechanical stresses placed upon them. Oneof the primary forces is vibration, which has theunfortunate side effect of loosening bolts and screws.Vibration causes mechanical difficulties to the motorand to the equipment that it operates. Surroundingitems may also be affected.

    3. Electrical safety. The first issue here is to make surethat motors dont become the source of an electricalshock or fault. Another issue is to make sure thatmotors dont cause problems to the electrical systemon which they are installed.

    4. Operational circuits. One last concern is that the cir-cuits on which motors are installed can operate con-tinually and correctly. Motors place unusual demandson electrical circuits. First of all, they can require large

    60

  • starting currents. (Fully loaded motors can draw start-ing currents of 4 to 8 times their normal full-load cur-rent in some circumstances even higher.) They alsoput a lot of inductive reactance into electrical systems.And because of the high currents that some motorsdraw, they overheat electrical circuits more readilythan do many other types of loads.

    It is the responsibility of the installer to ensure that theequipment installed (in this case, electric motors) is safe forthe end user.

    The BasicsThe operation of electric motors involves not only currentand voltage but also magnetic fields and their associatedcharacteristics.

    Basically, all electric motors operate by using electromag-netic induction, which, simply put, is the interaction betweenconductors, currents, and magnetic fields. Any time an elec-trical current passes through a conductor (of which copperwires are the most common type), it causes a magnetic fieldto form around that conductor. This is one of the absolutelaws of physics. Conversely, any time a magnetic field movesthrough a conductor, it induces (causes to flow) an electricalcurrent in that conductor. Again, this is an absolute andunchangeable law of physics.

    The manipulation of these two laws, in combination withthe principles of magnetic attraction and repulsion, is thebasis for the operation of motors. The intelligent use of elec-tromagnetic induction turns electricity into physical force,thereby causing the motor to turn.

    Let us go just one step further and explain in a little moredetail how this occurs. These are the basic operations of anelectric motor, step by step: An electrical current is turned onand flows through the motors windings, causing a strongmagnetic field to form around the windings. This magneticfield attracts the rotor (the part in the center of the motor

    Motors, Controllers, and Circuits 61

  • 62 Motors, Controllers, and Circuits

    that turns the shaft is at the center of the rotor) and moves ittoward the magnetic field, causing the initial movement ofthe motor. This movement is perpetuated by any one of var-ious means of rotating the magnetic field. The most commonmethod is to use several different windings to which currentis sent alternately, thus causing magnetic strength to be inone place one moment and another place the next. The rotorthen follows these fields, creating continuous motion.

    Although there are any number of variations and modifi-cations to these basic operations, these are the principles bywhich all motors function. Depending on the type of motordesign, you can increase or decrease power, operate at differ-ent voltages, and control motor speed.

    Motor MountingsIn general, motors must be installed so that adequate ventila-tion is provided and maintenance operations can be per-formed without difficulty.

    Open motors (motors whose windings are not fullyenclosed) with commutators or collector rings must belocated so that sparks from the motors cannot reach com-bustible materials. However, this does not prohibit installa-tion of these motors on wooden floors.

    Suitably enclosed motors must be used in areas where sig-nificant amounts of dust are present.

    One of the most important considerations for the mount-ing of electric motors is that they be installed so that vibra-tion wont be a problem. Generally, this requires a carefulmounting using strong fasteners. If you suspect that therewill be trouble with vibration, there are special antivibrationmountings that you can use to minimize the difficulty.

    When fastening to a concrete base, the ideal method is tohave J-bolts installed in the concrete pour. In such a case,templates must be carefully prepared prior to the pour.Placement of the templates must be double-checked on theday the concrete is poured into place.

  • Consider using a large-size lag shield or a lead anchor inpre-existing concrete. Maximum strength is of utmostimportance in these cases. If the anchor loosens, vibration ofthe motor will increase dramatically. This, of course, willcause the fastener to loosen further, and the motor will expe-rience serious difficulties in a fairly short time.

    When anchoring to a metal base, the base should bedrilled and tapped and the motor fastened to it with machinescrews and lock washers.

    When anchoring to a wood base, it is generally preferableto drill entirely through the wood and fasten the motor withcarriage bolts, fender washers, and lock washers. For smallmotors on strong wood bases, you can use a very large woodor sheet metal screw.

    MaintenanceWith all motors, it is necessary to provide regular mainte-nance. Even though most modern ac motors have no need oflubrication or changing of brushes as did older motors, theydo need to be periodically checked for problems. The chiefproblems to look for are vibration, overheating, and properalignment of any pulleys, gears, or belts.

    Fig. 4-1 shows a commonly used type of motor mainte-nance schedule that can be used to keep track of maintenanceoperations. It lists the motor number and location, basic oper-ating characteristics, and service data for a number of motors.

    Some maintenance mechanics prefer to keep a separatecard file, with an index card for each motor. And in recentyears, several types of computer programs have been devel-oped. These programs provide an easy way to save data on alarge number of motors. Any of these methods is effective,provided that you use it consistently.

    In general, every electrical motor in an industrial settingshould be carefully serviced at least once per month. Someolder motors have grease fittings for lubrication; most newermotors dont. They should all be checked regularly, however,and be given whatever attention they need.

    Motors, Controllers, and Circuits 63

  • 64 Motors, Controllers, and Circuits

    Fig. 4-1 Motor schedule.

    Conductors for Motor CircuitsProper sizing of motor conductors and overcurrent protec-tion are the most important factors in a motor installation.Fig. 4-2 is a brief outline of the various steps to be taken inmotor circuit design. Although these steps are explained indepth in this chapter, referring to a brief outline such as thisone is generally the quickest way to determine circuitrequirements.

    Branch-circuit conductors that supply single motors musthave an ampacity of at least 125 percent of the motors full-load current rating. (You will find full-load current ratings inTables 430.147 through 430.150 of the National ElectricalCode.) This is necessary because motors cause temporarysurges of current that could overheat the conductors if theyare not oversize.

    Motors used only for short cycles can have their branch-circuit ampacities reduced according to Table 430.22(E).

    DC motors fed by single-phase rectifiers must have theampacity of their conductors rated at 190 percent of the full-load current for half-wave systems and 150 percent of thefull-load current for full-wave systems. (This is because ofthe high levels of current that these motors can draw fromthe rectifiers.)

    MOTOR DATAFOR

    MOTOR STARTERVOLTAGEHP PHASE SERIALNO.

    FRAME AMPS RPM CODEMAKE NEMA

    RATINGCOILNO.

    STRSIZE

    MACHINEDRIVEN

    MOTORNO.

  • Fig. 4-2 Sizing of motor circuitry.

    For phase converters, the single-phase conductors thatsupply the converter must have an ampacity of at least 2.16times the full-load current of the motor or load being served.(This assumes that the voltages are equal. If they are not, thecalculated current must be multiplied by the result of outputvoltage divided by input voltage.)

    For One Motor:

    1. Determine full-load current of motor(s) (Table 430.150 for 3 phase).2. Multiply full-load current 1.25 to determine minimum conductor ampacity (Section 430.22(A)).3. Determine wire size (Table 310.16).4. Determine conduit size. (Table C4).5. Determine minimum fuse or circuit breaker size (Table 430.72(B)) (Section 240.6).6. Determine overload rating (Section 430.32(C )).

    For more than one motor:

    1. Perform steps 1 through 6 as shown above for each motor.2. Add full-load current of all motors, plus 25% of the full-load current of the largest motor to determine minimum conductor ampacity (Section 430.24)3. Determine wire size (Table 310.16).4. Determine conduit size. (Table C4).5. Add the fuse or circuit breaker size of the largest motor, plus the full-load currents of all other motors to determine the maximum fuse or circuit breaker size for the feeder (Section 430.24) (Section 240.6).

    DESIGNING MOTOR CIRCUITS

    Motors, Controllers, and Circuits 65

  • 66 Motors, Controllers, and Circuits

    Conductors connecting secondaries of continuous-dutywound-rotor motors to their controllers must have anampacity of at least 125 percent of the full-load secondarycurrent.

    When a resistor is installed separately from a controller,the ampacity of the conductors between the controller andthe resistor must be sized according to Table 430.23(C).

    Conductors That Supply Several Motors or Phase ConvertersConductors that supply two or more motors must have anampacity of no less than the total of the full-load currents ofall motors being served, plus 25 percent of the highest ratedmotor in the group. If interlock circuitry guarantees that allmotors cant be operated at the same time, the calculationscan be made based on the largest group of motors that canbe operated at any time.

    Several motors can be connected to the same branch cir-cuit if the following requirements are met:

    1. Motors installed on general-purpose branch circuitswithout overload protection are motors of only 1horsepower or less (assuming the installation complieswith all other requirements).

    2. The full-load current is not more than 6 amperes.3. The branch-circuit protective device rating marked on

    any controllers is not exceeded.

    Conductors supplying two or more motors must be pro-vided with a protective device rated no greater than the high-est rating of the protective device of any motor in the groupplus the sum of the full-load currents of the other motors.

    Where heavy-capacity feeders are to be installed forfuture expansions, the rating of the feeder protective devicescan be based on the ampacity of the feeder conductors.

  • Phase converters must have an ampacity of 1.73 times thefull-load current rating of all motors being served, plus 25percent of the highest rated motor in the group. (Thisassumes that the voltages are equal. If they are not, the cal-culated current must be multiplied by the result of outputvoltage divided by input voltage.) If the ampere rating of the3-phase output conductors is less than 58 percent of the rating of the single-phase input current ampacity, separateovercurrent protection must be provided within 10 ft of thephase converter.

    Conductors That Supply Motors and Other LoadsConductors that supply both motors and other loads musthave their motor loads computed as specified above, otherloads computed according to their specific Code require-ments, and all loads then added together.

    If taps are to be made from feeder conductors, they mustterminate in a branch-circuit protective device and must:

    1. Have the same ampacity as the feeder conductors; OR

    2. Be enclosed by a raceway or in a controller, and be nolonger than 25 ft;

    OR3. Have an ampacity of at least one-third of the feeder

    ampacity, be protected, and be no longer than 25 ft.

    A tap circuit is illustrated in Fig. 4-3.In high-bay manufacturing buildings (more than 25 ft

    from floor to ceiling, measured at the walls), taps longerthan 25 ft are permitted. In these cases:

    1. Tap conductors must have an ampacity of at least one-third that of the feeder conductors.

    2. Tap conductors must terminate in an appropriate cir-cuit breaker or set of fuses.

    Motors, Controllers, and Circuits 67

  • 68 Motors, Controllers, and Circuits

    3. Tap conductors must be protected from damage andbe installed in a raceway.

    4. Tap conductors must be continuous, with no splices.5. The minimum size of tap conductors is No. 6 AWG

    copper or No. 4 AWG aluminum.6. Tap conductors cant penetrate floors, walls, or

    ceilings.7. Tap conductors may be run no more than 25 ft hori-

    zontally and no more than 100 ft overall.

    Fig. 4-3 Tap circuits not over 25 ft long.

    Feeders that supply motors and lighting loads must besized to carry the entire lighting load plus the motor load.

    GroundingAs with virtually all other electrical equipment, motors needto be grounded to maintain safety. There are rare exceptions,but the requirement applies to almost all motors. Groundingrequirements are generally as follows: