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a b c d e f g h i j k l m n o p q r s t u v w x y z


alternating current current that reverses its direction of flow at periodic intervals


ambient air temperature the temperature of the surrounding air

American Wire Gauge (AWG) an English standard for measuring the diameter of wire

  ammeter a device for measuring current flow

ammeter shunt a device that allows an ammeter to measure large amounts of current; the shunt is connected in series with the load and the ammeter is connected in parallel with the shunt


amp a measure of electric current defined as one coulomb per second

  ampacity the amount of current that a wire can carry
  amplitude the maximum height reached by a waveform

analog meters meters that employ a moving pointer to indicate a value


angle theta (_u) the phase angle difference between

voltage and current in a circuit containing a reactive component such as an inductor or capacitor


apparent power (VA) the value found by multiplying the applied voltage by the total current of an AC circuit. Apparent power is measured in volt-amps (VA) and should not be confused with true power, measured in watts.


apparent power volt amps (VA) the product of the total applied voltage and the total current flow in an AC circuit


appear to flow the charging and discharging of a capacitor will cause current to appear to flow through a capacitor when it is connected to an AC circuit


artificial respiration a method of providing oxygen to a

person unable to breath on his or her own


atom the smallest part of an element, atoms are composed of three primary sub atomic particles; the proton, the neutron, and the electron


atomic number the number of protons located in the nucleus of an atom


attraction generally the force that exists between objects that contain opposite charges


autotransformer a transformer that uses only one winding for both the primary and secondary


average the value of voltage when an AC sine wave voltage is changed to DC


bidirectional a device that can conduct current in either direction, or current that flows in two directions


British thermal unit (BTU) the amount of heat necessary to change the temperature of one pound of water one degree Fahrenheit


capacitive reactance (Xc) the current-limiting effect of a



carbon film resistor a resistor made by coating a nonconducting material with a film of carbon


centrifugal force the force that causes a spinning object to pull away from its axis point


centrifugal switch a switch used to disconnect the start windings in a split-phase motor after the motor has accelerated to approximately 75% of rated speed


chassis ground a conductor connected to the metal case of a piece of equipment for the purpose of placing the case at ground potential


circuit branch (a) in the case of parallel circuits, a circuit derived from a main set of circuit conductors that supply power to multiple other circuits; (b) normally the circuit that supplies power to electrical equipment from the last protective device, such as a fuse or circuit breaker


circuit breakers devices that disconnect power to a circuit in the event of an excessive amount of current


circular mil an English measure for determining the crosssectional area of round wire; circular mils is the diameter in mils (1 mil 5 0.001 in.) squared


clamp-on ammeter an ammeter with a movable jaw that can be clamped around a conductor to measure current flow

color code a method of marking the resistance and tolerance of a resistor with bands of color


combination circuit a circuit that contains both series

and parallel circuits


compensating winding a winding used in universal motors

to counteract the inductive reactance in the armature windings


complete path an electric circuit that exists from the

more negative to the more positive voltage

composition carbon resistor a resistor that is made by combining carbon with a resin material

conductive compensation accomplished by connecting the compensating winding of a universal motor in series with the field winding

  conductors materials that conduct electricity easily
  confined space a space that has limited entrances or exits

control transformer a common type of transformer used in motor control circuits to reduce the rated line voltage to the amount needed to operate the control components

conventional current flow theory an older theory stating that electric current flows from the more positive source to the more negative source


correction factor a decimal fraction employed to determine the amount of current a conductor is permitted to carry over a range of ambient temperature


coulomb a quantity measure of electrons that equals


  CPR an acronym for cardiopulmonary resuscitation

current adds one of the three rules used to solve values of voltage, current, resistance, and power in a parallel circuit


current divider formula a formula used to calculate the amount of current flow in any branch when the total circuit current and resistance are known


current flow through the inductor (IL) the amount of current flowing through the inductor


current lags voltage the relationship of current and voltage in a pure inductive circuit


current transformer a transformer used to measure large values of AC current


cycle one cycle is completed when an AC voltage completes 360 degrees


d’Arsonval movement a galvanometer that employs a moving coil suspended inside a permanent magnet to move a pointer


damp location a location that is covered and not likely to be saturated by water


de-energized circuit a circuit that has been disconnected from the power supply

  dielectric the insulation between the plates of a capacitor

dielectric stress the stretching of the molecular structure of the dielectric


direct current (DC) current that flows in only one direction


disconnect to turn off or remove power from a circuit


distribution transformer a transformer that is generally used to lower the power company line voltage to the value needed for houses or industrial plants


dry location a location that is not normally subject to

dampness or wetness




earth ground point at which a metal rod is driven into the ground to provide a low-resistance path to the earth


eddy current electric currents induced in metal; generally core material of motors and transformers


egress an entrance or exit into a structure


electrolytic a type of capacitor that is polarity sensitive


electromotive force (EMF) the force known as voltage that pushes the electrons through an electric circuit


electron orbit the space in which an electron circles thenucleus of an atom


electron theory the theory stating that electricity flows

from the more negative power source to the more positive power source


electron a sub atomic particle that orbits the nucleus of an atom and contains a negative charge


electrostatic charge the charge of a capacitor produced by the stressing of the molecules in the dielectric


element a material, the smallest part of which would be anatom


energized circuit a circuit connected to the power supply; a voltage or potential exists between conductors


excitation current the amount of current that flows in the primary winding of a transformer when no load is connected to the secondary


exponential the rate at which a capacitor charges and discharges


exponential curve a rate at which current increases or decreases in an inductor




farad the unit measure of capacitance


fibrillation a condition in which the heart starts to quiver

and stops its pumping action


fire retardant clothing clothing made from a specially

treated material that resists ignition; many industries require electricians to wear this type of clothing


flux leakage the amount of magnetic flux lines that radiate into the air


frequency the number of complete cycles that occur in one second


frequency the number of times per second that the current changes direction in an alternating current circuit


fuses devices that disconnect power to a circuit in the

event of an excessive amount of current




galvanometers very sensitive meters that require only a few microamperes of current to operate


general voltage divider formula a formula employed to determine the value of resistance needed to produce a certain voltage drop


ground point point at which a circuit or device is



grounding conductor generally the bare or green wireused to establish a low resistance path to ground




henry the standard measure of inductance


hertz a measure of frequency


HIPOT an instrument that develops a high potential or high voltage for testing the dielectric of a capacitor

Holtz motor a type of single-phase synchronous
that operates at a speed of 1200 RPM


horseplay playing practical jokes or exhibiting adolescent behavior in an inappropriate place


horsepower a common measure of power in which the base is established at 550 pound feet per second; in electrical quantities, 746 watts equals one horsepower


hysteresis loss the amount of power loss in the form of

heat caused by molecular friction




idiot proofing designing a piece of equipment so it cannotbe misused by an experienced person


impedance the total current limiting effect in an electric

circuit; impedance is measured in ohms.


impedance (Z) the total current-limiting effect in an AC



in phase a condition that occurs when the voltage and current reach peak values and zero crossing at the same time


induced voltage voltage that is supplied to a conductor

by cutting lines of magnetic flux


inductance (L) the property of an electric circuit whereby voltage is produced by cutting magnetic flux lines

inductive compensation accomplished by shorting the compensating winding leads together and permitting induced voltage to supply current to the winding


inductive reactance (XL) the current-limiting effect of a pure inductor


inrush current the amount of current flow that occurs

when power is first applied to a transformer


insulation the plastic or rubber coating around the conductor


insulators materials that hinder the flow of electricity

isolation transformers transformers that have their primary and secondary windings electrically separated from each other




joule a metric measure of power similar to the English measure watt




laminated the process of stacking thin sheets of metal together to form the core material for a transformer


leakage current the amount of current that flows through the dielectric of a capacitor


Lenz’s law an electrical law stated by a scientist named

Lenz that says, basically, that an induced voltage will always oppose the force that induces it


linear wave a waveform that increases in the same proportion as the angle of rotation


load the amount of power a circuit is supplying to a device


lock out and tag out a procedure to prevent a circuit

from being energized accidentally




magnetic induction using magnetic field to induce a voltage into a conductive material, generally wire


matter any material composed of atoms


maximum operating temperature the maximum temperature in an area where the wire is to be used


MEGGER® a device used to measure the insulation resistance; meggers measure resistance in millions of ohms

metal film resistor a resistor made by coating a nonconducting material with a film of metal


metal glaze resistor a resistor made by combining glass and metal


metal oxide varistor (MOV) an electronic device that exhibits a rapid change of resistance with a change of temperature


meter an instrument used to test for some electrical quantity such as voltage, current, or resistance


mil foot an English standard of measure for wire; a mil foot is a piece of wire one thousandth of an inch in diameter and one foot long


milliamperes one milliampere equals 1/1000 of an amp



molecules a combination of atoms that form the smallest part of a compound


MSDS an acronym for material safety data sheets


multirange voltmeters voltmeters that employ more than one full range value


multispeed motors motors designed to operate at more than one full load speed

multiturn variable resistors resistors constructed so

that their ohmic value can be adjusted by turning a shaft

from three to ten turns




National Electrical Code a national standard for installation of electrical apparatus and equipment published by the National Fire Protection Association


negative a charge formed by an excess of electrons


neutral conductor a conductor is generally grounded and is a common connection to other parts of a circuit


neutral conductor the part of an electric circuit that is

generally grounded


neutral plane the point at which no voltage is induced in the armature winding


neutron one of the principal parts of an atom. The neutron has no charge and is part of the nucleus.


node a point of connection


nonpolarized capacitors capacitors that are not sensitive to voltage polarity


nucleus the center or core of an object




ohm (V) the unit of measure used to describe the resistance to the flow of electric current


Ohm’s law a set of mathematical formulas developed by

the German scientist Georg S. Ohm


ohmmeter a meter used to measure values of resistance one of three formulas used to determine the total resistance of resistors connected in parallel


oscillators devices used to convert direct current into alternating current


OSHA an acronym for Occupational Safety and Health Administration


out of phase a condition that occurs between the voltage and current in a capacitive circuit




parallel block a section of a combination circuit composed of parallel resistors


parallel circuits circuits with more than one path for current flow

  parallel conductors conductors connected in parallel with each other for the purpose of carrying more electric current

parallelogram method a method of obtaining values of voltage, current, impedance, and power with vectors


peak the maximum value obtained by a waverform


plates thin, flat metal used in the construction of a capacitor


polarized capacitors capacitors that are sensitive to voltage polarity


positive a charge formed by a lack of electrons


pot slang for potentiometer


potentiometer a variable resistor employed in such a

manner that it can provide a variable voltage


power the ability to do work; in an electric circuit, it is

generally measured in watts


power factor (PF) the ratio of true power to apparent



primary winding the winding of a transformer to which

power is connected


product over sum formula one of three formulas used to determine the total resistance of resistors connected in parallel


proton a sub-atomic particle located in the nucleus of an atom; the proton has a positive charge




quadrature power often referred to as VARs, reactive power, or wattless power


quality (Q) the ratio of capacitive reactance to resistance in a capacitor


quality (Q) the ratio of inductive reactance as compared

with resistance




RC time constant the time required for a capacitor to charge or discharge when it is connected in series with a resistance


reactance the property of a circuit that limits current by

means other than resistance


reactive power (VARs) volt amps reactive; often called wattless power, VARs is the product of the current and voltage in a pure reactive load


reactive power (VARs) Volt-Amps Reactive; often referred to as wattless power


reciprocal formula one of three formulas used to determine the total resistance of resistors connected in parallel


reduce a method employed to simplify parallel or series

connected components into a single resistor


repulsion generally the force that exists between two objects that contain like electrical charges


resistance the element of an electric circuit that can limit the flow of current by producing heat


resistance adds one of the major rules concerning series circuits


resistive loads loads that employ resistance to limit circuit current


rheostat a variable resistor that contains only two terminals


ripple the turning on and off effect that occurs when alternating current is converted into direct current


R-L time constant the amount of time required for current to increase or decrease in value


root mean square (RMS) the amount of AC voltage that will produce the same heating effect as a like amount of DC voltage


run winding one of the windings in a split-phase motor




scaffold a platform for working in high places, generally designed so it can be taken apart and transported to a different job site or area


secondary winding the winding of a transformer to which the load is connected


series circuit a circuit that contains only one path for current flow


series resistance resistance connected in series with

other circuit components

shaded-pole induction motor a single-phase motor that produces a rotating magnetic field by shading one side of each pole piece; shading is accomplished by placing a loop of large copper wire around one side of the pole piece


shading coil the loop of large wire used to form a shaded pole


short circuit a circuit that contains almost no resistance

to limit the flow of current


sine wave a waveform produced by any rotating machine. The voltage at any point on the waveform can be determined by multiplying the peak value by the sine of the angle of rotation


skin effect the effect that causes electrons to move toward the outside of a conductor in an alternating current circuit


split-phase motor a type of single-phase motor that

splits the current flow through two separate windings to produce a rotating magnetic field


start winding one of the windings used in a split-phase



step-down transformer a transformer that produces a lower secondary voltage than primary voltage


step-up transformer a transformer that produces a higher secondary voltage than primary voltage


strength of magnetic field the number of magnetic flux lines per square inch or flux density of a magnetic field


surface area one of the factors that determines the

amount of capacitance a capacitor will have


synchronous motors motors that operate at a constant speed from no load to full load


synchronous speed the speed of the rotating magnetic field of an AC induction motor




tape wound core a type of transformer core made by winding a long continuous metal sheet in a circular or

rounded-rectangle shape


tolerance the range over which a resistor is considered to be within its marked value


toroid core a transformer core that is in a toroid shape,

which is generally round with a hole in the center similar to a donut


total current (IT) the total current flow in an electric circuit


total current (IT) the total current flow in an electric circuit; in an RL parallel circuit it is determined by vector addition

of the resistive current and inductive current


total impedance the total current-limiting effect in an AC circuit


total impedance the total current-limiting effect in an AC circuit


trace the current path a method used to determine if

components are connected in series or parallel


transformer an electrical machine used to change values of voltage, current, and impedance


triangle wave a linear waveform in which the voltage is proportional to the peak value and percent of angle of rotation


true power the amount of electrical energy that is converted into some other form of energy such as thermal or kinetic; also known as watts


turns of wire the number of turns of wire on a coil


turns ratio the ratio of the number of turns of wire in the primary winding compared with the number of turns in the secondary winding


two phase a power system that produces two separate

phase voltages 90° apart




unidirectional something that moves in only one direction


universal motor a type of single-phase motor that can operate on either direct or alternating current




valence electrons electrons located in the outermost orbit or shell of an atom

variable capacitors capacitors that can be adjusted for

different values of capacitance her12945_glo.qxd 9/13/02 7:32 AM Page 281

variable resistor a resistor whose resistance value can be changed


vector addition the process of using vectors to add like

electrical values


vector a line that indicates both magnitude and direction


volt a measure of EMF often described as electrical pressure


voltage divider a circuit generally constructed of series

connected resistors to provide different amounts of voltage


voltage divider a circuit used to provide different values of voltage


voltage drop the amount of voltage employed to push current through the resistance of the wire


voltage drop the amount of voltage existing across any

component that limits the flow of current; voltage drop indicates the amount of voltage necessary to push current

through a limiting element


voltage polarity the polarity, positive or negative, of the voltage at a certain point in a circuit


voltage rating the amount of voltage that can be safely

applied to a capacitor without damaging the dielectric


voltage spike a large amount of voltage that exists for a very short period of time


voltmeter a meter used to measure voltage


volts-per-turn ratio a method of determining voltage values in a transformer by dividing the number of turns of wire in the primary winding by the voltage applied voltage




Warren motor a type of single-phase synchronous motor that operates at a speed of 3600 RPM


watt a power measurement that describes the amount of electrical energy converted to some other form


wattless power VARs; computed by using values that pertain only to reactive components such as inductors or capacitors


watts a measure of electric power


watts the true power in a circuit; indicates the amount of electrical energy converted to some other form


weber a measure of magnetism equal to 100,000,000 lines of magnetic flux


wet location areas that are subject to saturation by water; some of these areas include direct burial in the earth, underground conduit installations, or installation in masonry or concrete slabs


wire wound resistor a resistor made with a high-resistance metal wire such as Nichrome