Access Fitting. A fitting that permits access to conductors in concealed
or enclosed wiring, elsewhere than at an outlet.
Active Electrical Network. A network that contains one or more
sources of electrical energy.
Admittance. The reciprocal of impedance.
Air-Blast Transformer. A transformer cooled by forced circulation
of air through its core and coils.
Air Circuit Breaker. A circuit breaker in which the interruption occurs
in air.
Air Switch. A switch in which the interruption of the circuit occurs
in air.
Alive. Electrically connected to a source of emf, or electrically
charged with a potential different from that of the earth. Also,
practical synonym for current-carrying or hot.
Alternating Current. A periodic current, the average value of which
over a period is zero.
Alternator. Synchronous generator; a synchronous alternatingcurrent
machine that changes mechanical power into electrical
Ambient Temperature. The temperature of a surrounding cooling
medium, such as gas or liquid, that comes into contact with the
heated parts of an apparatus.
Ammeter. An instrument for measuring electric current.
Ampere. A charge flow of one coulomb per second.
Annunciator. An electromagnetically operated signaling apparatus
that indicates whether a current is flowing or has flowed in one
or more circuits.
Apparent Power. In a single-phase, two-wire circuit, the product of
the effective current in one conductor multiplied by the effective
voltage between the two points of entry.
Appliance. Current-consuming equipment, fixed or portable, such
as heating or motor-operated equipment.
Arc-Fault Circuit Interrupter (AFCI). An electrical device that detects
the unique electronic characteristics of electrical arcs. If an
arc is sensed, the device further deenergizes the circuit to which it
is connected.
Arcing Contacts. Contacts on which an arc is drawn after the main
contacts of a switch or circuit breaker have parted.
Arcing Time of Fuse. The time elapsing from the severance of the
fuse link to the final interruption of the circuit under specified
Arc-Over of Insulator. A discharge of power current in the form of
an arc, following a surface discharge over an insulator.
Armor Clamp. A fitting for gripping the armor of a cable at the
point where the armor terminates, or where the cable enters a
junction box or other apparatus.
Armored Cable. A cable provided with a wrapping of metal, usually
steel wires, primarily for the purpose of mechanical protection.
Arrester, Lightning. A device that reduces the voltage of a surge
applied to its terminals and restores itself to its original operating
Autotransformer. A transformer in which part of the winding is
common to both the primary and secondary circuits.
Back-Connected Switch. A switch in which the current-carrying
conductors are connected to studs in back of the mounting base.
Bank. An assemblage of fixed contacts in a rigid unit over which
wipers or brushes may move and make connection with the
Bank, Duct. An arrangement of conduit that provides one or more
continuous ducts between two points.
Benchboard. A switchboard with a horizontal section for control
switches, indicating lamps, and instrument switches; may also
have a vertical instrument section.
Bidirectional Current. A current that has both positive and negative
Bond, Cable. An electrical connection across a joint in the armor
or lead sheath of a cable, between the armor or sheath to ground,
or between the armor or sheath of adjacent cables.
Box, Conduit. A metal box adapted for connection to conduit for
installation of wiring, making connections, or mounting devices.
Box, Junction. An enclosed distribution panel for connection or
branching of one or more electric circuits without making permanent
Box, Junction (Interior Wiring). A metal box with blank cover for
joining runs of conduit, electrical metallic tubing, wireway, or
raceway and for providing space for connection and branching of
enclosed conductors.
Box, Pull. A metal box with a blank cover which is used in a run of
conduit or other raceway to facilitate pulling in the conductors; it
may also be installed at the end of one or more conduit runs for
distribution of the conductors.
Branch Circuit. That portion of a wiring system extending beyond
the final automatic overload protective device.
Branch Circuit, Appliance. A circuit supplying energy either to permanently
wired appliances or to attachment-plug receptacles such
as appliance or convenience outlets and having no permanently
connected lighting fixtures.
Branch Circuit Distribution Center. A distribution circuit at which
branch circuits are supplied.
Branch Circuit, Lighting. A circuit supplying energy to lighting outlets
Branch Conductor. A conductor that branches off at an angle from
a continuous run of conductor.
Break. The break of a circuit-opening device is the minimum distance
between the stationary and movable contacts when the device
is in its open position.
Breakdown. Also termed puncture, denoting a disruptive discharge
through insulation.
Breaker, Line. A device that combines the functions of a contactor
and a circuit breaker.
Buried Cable. A cable installed under the surface of the soil in such
a manner that it cannot be removed without digging up the soil.
(Type UF is commonly used for home wiring.)
Bus. A conductor or group of conductors that serves as a common
connection for three or more circuits in a switchgear
Bushing. Also termed insulating bushing; a lining for a hole for insulation
and/or protection from abrasion of one or more conductors
passing through it.
Cabinet. An enclosure for either surface or flush mounting, provided
with a frame, mat, or trim.
Cable. The package of wires, insulating material, sheathing, and
whatever else is necessary for the type being installed. It is usually
purchased in large spools.
Cable Fault. A partial or total local failure in the insulation or continuity
of the conductor.
Cable Joint. Also termed a splice; a connection between two
or more individual lengths of cables, with their conductors
individually connected, and with protecting sheaths over the
Cable, Service. Service conductors arranged in the form of a cable
(see Service).
Cable Sheath. The protective covering, such as lead or plastic, applied
over a cable.
Charge, Electric. An inequality of positive and negative electricity
in or on a body. The charge stored in a capacitor (condenser)
corresponds to a deficiency of free electrons on the positive
plate and to an excess of free electrons on the negative
Choke Coil. A low-resistance coil with sufficient inductance to substantially
impede ac or transient currents.
Circuit, Electric. A conducting path through which electric charges
may flow. A dc circuit is a closed path for charge flow; an ac circuit
is not necessarily closed and may conduct in part by means of an
electric field (displacement current).
Circuit, Earth (Ground) Return. An electric circuit in which the
ground serves to complete a path for charge flow.
Circuit, Magnetic. A closed path for establishment of magnetic flux
(magnetic field) that has the direction of the magnetic induction
at every point.
Cleat. An assembly of a pair of insulating material members with
grooves for holding one or more conductors at a definite distance
from the mounting surface.
Clip, Fuse. Contacts on a fuse support for connecting a fuse holder
into a circuit.
Closed-Circuit Voltage. The terminal voltage of a source of electricity
under a specified current demand.
Closed Electric Circuit. A continuous path or paths providing for
charge flow. In an ac closed circuit, charge flow may be changed
into displacement current through a capacitor (condenser).
Coercive Force. The magnetizing force at which the magnetic induction
is zero at a point on the hysteresis loop of a magnetic
Coil. A conductor arrangement (basically a helix or spiral) that concentrates
the magnetic field produced by electric charge flow.
Composite Conductor. A conductor consisting of two or more
strands of different metals, operated in parallel.
Concealed. To be made inaccessible by the structure or finish of a
building; also, wires run in a concealed raceway.
Condenser. Also termed capacitor; a device that stores electric
charge by means of an electric field.
Conductance. A measure of permissiveness to charge flow; the reciprocal
of resistance.
Conductor. A substance that has free electrons or other charge carriers
that permit charge flow when an emf is applied across the
Conduit. A structure containing one or more ducts; commonly
formed from iron pipe or electrical metallic tubing (EMT).
Conduit Fittings. Accessories used to complete a conduit system,
such as boxes, bushings, and access fittings.
Conduit, Flexible Metal. A flexible raceway of circular form for enclosing
wires or cables; usually made of steel wound helically and
with interlocking edges and a weather-resistant coating. Sometimes
called Greenfield.
Conduit, Rigid Steel. A raceway made of mild steel pipe with a
weather-resistant coating.
Conduit Run. A duct bank; an arrangement of conduit with a continuous
duct between two points in an electrical installation.
Contactor. An electric power switch, not operated manually, designed
for frequent operation.
Contacts. Conducting parts that employ a junction that is opened
or closed to interrupt or complete a circuit.
Control Relay. A relay used to initiate or permit a predetermined
operation in a control circuit.
Coulomb. An electric charge of 6.28 × 1018 electrons. One coulomb
is transferred when a current of one ampere continues past a point
for one second.
Counter EMF. CEMF; the effective emf within a system which opposes
current in a specified direction.
Current. The rate of charge flow. A current of one ampere is equal
to a flow rate of one coulomb per second.
Cycle. The complete series of values that occurs during one period
of a periodic quantity. The unit of frequency, the hertz, is equal
to one cycle per second.
Dead. Functionally conducting parts of an electrical system that
have no potential difference or charge (voltage of zero with respect
to ground).
Degree, Electrical. An angle equal to 1/360 of the angle between
consecutive field poles of like polarity in an electrical machine.
Diagram, Connection. A drawing showing the connections and interrelations
of devices employed in an electrical circuit.
Dielectric. A medium or substance in which a potential difference
establishes an electric field that is subsequently recoverable as
electric energy.
Direct Current. Aunidirectional current with a constant value. Constant
value is defined in practice as a value that has negligible
Direct EMF. Also termed direct voltage; anemf that does not change
in polarity and has a constant value (one of negligible variation).
Discharge. An energy conversion involving electrical energy. Examples
include discharge of a storage battery, discharge of a capacitor,
and lightning discharge of a thundercloud.
Displacement Current. The apparent flow of charge through a dielectric
such as in a capacitor; represented by buildup and/or decay
of an electric field.
Disruptive Discharge. A rapid and large current increase through
an insulator due to insulation failure.
Distribution Center. A point of installation for automatic overload
protective devices connected to buses where an electrical supply
is subdivided into feeders and/or branch circuits.
Divider, Voltage. A tapped resistor or series arrangement of resistors,
sometimes with movable contacts, providing a desired IR
drop. (A voltage divider is not continuously and manually variable
as in a potentiometer).
Drop, Voltage. An IR voltage between two specified points in an
electric circuit.
Duct. A single enclosed runway for conductors or cables.
Effective Value. The effective value of a sine-wave ac current or voltage
is equal to 0.707 of peak. Also called the root-mean-square
Glossary 423
(rms) value, it produces the same I 2R power as an equal dc
Efficiency. The ratio of output power to input power, usually expressed
as a percentage.
Electrical Units. In the practical system, electrical units comprise the
volt, the ampere, the ohm, the watt, the watt-hour, the coulomb,
the mho, the henry, the farad, and the joule.
Electricity. A physical entity associated with the atomic structure of
matter that occurs in polar forms (positive and negative) and that
are separable by expenditure of energy.
Electrode. A conducting substance through which electric current
enters or leaves in devices that provide electrical control or energy
Electrolyte. A substance that provides electrical conduction when
dissolved (usually in water.)
Electrolytic Conductor. Flow of electric charges to and from electrodes
in an electrolytic solution.
Electromagnetic Induction. A process of generation of emf by movement
of magnetic flux that cuts an electrical conductor.
Electromotive Force (EMF). An energy-charge relation that results
in electric pressure, which produces or tends to produce charge
flow (see Voltage).
Electron. The subatomic unit of negative electricity; it is a charge of
1.6 × 10−19 coulomb.
Electronics. The science dealing with charge flow in vacuum, gases,
and crystal lattices.
Electroplating. The electrical deposition of metallic ions as neutral
atoms on an electrode immersed in an electrolyte.
Electrostatics. A branch of electrical science dealing with the laws
of electricity at rest.
Energy. The amount of physical work a system is capable of doing.
Electrical energy is measured in watt-seconds (the product of
power and time).
Entrance, Duct. An opening of a duct at a distributor box or other
accessible location.
Equipment, Service. A circuit breaker or switches and fuses with
their accessories, installed near the point of entry of service conductors
to a building.
424 Glossary
Exciter. An auxiliary generator for supplying electrical energy to the
field of another electrical machine.
Farad. A unit of capacitance defined by the production of one volt
across the capacitor terminals when a charge of one coulomb is
Fault Current. An abnormal current flowing between conductors or
from a conductor to ground due to an insulation defect, arc-over,
or incorrect connection.
Feeder. A conductor or a group of conductors for connection of generating
stations, substations, generating stations and substations,
or a substation and a feeding point.
Ferromagnetic Substance. A substance that has a permeability considerably
greater than that of air; a ferromagnetic substance has a
permeability that changes with the value of applied magnetizing
Filament. A wire or ribbon of conducting (resistive) material that
develops light and heat energy due to electric charge flow; light
radiation is also accompanied by electron emission.
Fixture Stud. A fitting for mounting a lighting fixture in an outlet
box and which is secured to the box.
Flashover. A disruptive electrical discharge around or over (but not
through) an insulator.
Fluorescence. An electrical discharge process involving radiant energy
transferred by phosphors into radiant energy that provides
increased luminosity.
Flux. Electrical field energy distributed in space, in a magnetic substance,
or in a dielectric. Flux is commonly represented diagrammatically
by means of flux lines denoting magnetic or electric
Force. An elementary physical cause capable of modifying the motion
of a mass.
Frequency. The number of periods occurring in unit time of a periodic
process such as in the flow of electric charge.
Frequency Meter. An instrument that measures the frequency of an
alternating current.
Fuse. A protective device with a fusible element that opens the circuit
by melting when subjected to excessive current.
Fuse Cutout. An assembly consisting of a fuse support and holder,
which may also include a fuse link.
Glossary 425
Fuse Element. Also termed fuse link; the current-carrying part
of a fuse that opens the circuit when subjected to excessive
Fuse Holder. A supporting device for a fuse that provides terminal
Galvanometer. An instrument for indicating or measuring comparatively
small electric currents. A galvanometer usually has zerocenter
Gap. Spark gap; a high-voltage device with electrodes between
which a disruptive discharge of electricity may pass, usually
through air. A sphere gap has spherical electrodes; a needle gap
has sharply pointed electrodes; a rod gap has rods with flat
Ground. Also termed earth; a conductor connected between a circuit
and the soil. A chassis ground is not necessary at ground potential
but is taken as a zero-volt reference point. An accidental
ground occurs due to cable insulation faults, an insulator defect,
and so on.
Ground-Fault Interrupter (GFI). A device installed in circuits where
current leakage can be especially dangerous, such as outdoor or
bathroom circuits. It shuts off current flow within 0.025 second
at the onset of a leak as small as 5 milliamperes.
Grounding Electrode. A conductor buried in the earth for connection
to a circuit. The buried conductor is usually a cold-water
pipe, to which connection is made with a ground clamp.
Ground Lug. A lug for convenient connection of a grounding conductor
to a grounding electrode or device to be grounded.
Ground Outlet. An outlet provided with a polarized receptacle with
a grounded contact for connection of a grounding conductor.
Ground Switch. A switch for connection or disconnection of a
grounding conductor.
Guy. A wire or other mechanical member having one end secured
and the other end fastened to a pole or structural part maintained
under tension.
Hanger. Also termed cable rack; a device usually secured to a wall
to provide support for cables.
Heat Coil. A protective device for opening and/or grounding a circuit
by switching action when a fusible element melts due to excessive
426 Glossary
Heater. In the strict sense, a heating element for raising the temperature
of an indirectly heated cathode in a vacuum or gas tube. Also
applied to appliances such as space heaters and radiant heaters.
Henry. The unit of inductance; it permits current increase at the rate
of 1 ampere per second when 1 volt is applied across the inductor
Hickey. A fitting for mounting a lighting fixture in an outlet box.
Also, a device used with a pipe handle for bending conduit.
Horn Gap. A form of switch provided with arcing horns for automatically
increasing the length of the arc and thereby extinguishing
the arc.
Hydrometer. An instrument for indicating the state of charge in a
storage battery.
Hysteresis. The magnetic property of a substance which results from
residual magnetism.
Hysteresis Loop. A graph that shows the relation between magnetizing
force and flux density for a cyclically magnetized
Hysteresis Loss. The heat loss in a magnetic substance due to application
of a cyclic magnetizing force to a magnetic substance.
Impedance. Opposition to ac current by a combination of resistance
and reactance; impedance is measured in ohms.
Impedances, Conjugate. A pair of impedances that have the same resistance
values, and that have equal and opposite reactance values.
Impulse. An electric surge of unidirectional polarity.
Indoor Transformer. A transformer that must be protected from the
Induced Current. A current that results in a closed conductor due
to cutting of lines of magnetic force.
Inductance. An electrical property of a resistanceless conductor,
which may have a coil form and which exhibits inductive reactance
to an ac current. All practical inductors also have at least a
slight amount of resistance.
Inductor. A device such as a coil with or without a magnetic core
which develops inductance, as distinguished from the inductance
of a straight wire.
Instantaneous Power. The product of an instantaneous voltage by
the associated instantaneous current.
Glossary 427
Instrument. An electrical device for measurement of a quantity under
observation or for presenting a characteristic of the quantity.
Interconnection, System. A connection of two or more power systems.
Interconnection Tie. A feeder that interconnects a pair of electric
supply systems.
Interlock. An electrical device whose operation depends on another
device for controlling subsequent operations.
Internal Resistance. The effective resistance connected in series with
a source of emf due to resistance of the electrolyte, winding resistance,
and so on.
Ion. A charged atom, or a radical. For example, a hydrogen atom
that has lost an electron becomes a hydrogen ion; sulphuric acid
produces H+ and SO−4 ions in water solution.
IR Drop. A potential difference produced by charge flow through a
Isolating Switch. An auxiliary switch for isolating an electric circuit
from its source of power; it is operated only after the circuit has
been opened by other means.
Joule. A unit of electrical energy, also called a watt-second. One
joule is the transfer of one watt for one second.
Joule’s Law. The rate at which electrical energy is changed into heat
energy is proportional to the square of the current.
Jumper. A short length of conductor for making a connection between
terminals, around a break in a circuit, or around an electrical
Junction. Apoint in a parallel or series-parallel circuit where current
branches off into two or more paths.
Junction Box. An enclosed distribution panel for the connection or
branching of one or more electrical circuits without using permanent
splices. In the case of interior wiring, a junction box consists
of a metal box with a blank cover; it is inserted in a run of conduit,
raceway, or tubing.
Kirchhoff’s Law. The voltage law states that the algebraic sum of
the drops around a closed circuit is equal to zero. The current law
states that the algebraic sum of the currents at a junction is equal
to zero.
Knockout. A scored portion in the wall of a box or cabinet which
can be removed easily by striking with a hammer; a circular
428 Glossary
hole is provided thereby for accommodation of conduit or
kVA. Kilovolt-amperes; the product of volts and amperes divided
by 1000.
Lag. Denotes that a given sine wave passes through its peak at a
later time than a reference sine wave.
Lamp holder. Also termed socket or lamp receptacle; a device for
mechanical support of and electrical connection to a lamp.
Lay. The lay of a helical element of a cable is equal to the axial
length of a turn.
Lead. Denotes that a given sine wave passes through its peak at an
earlier time than a reference sine wave.
Leakage, Surface. Passage of current over the boundary surfaces of
an insulator as distinguished from passage of current through its
Leg of a Circuit. One of the conductors in a supply circuit between
which the maximum supply voltage is maintained.
Lenz’s Law. States that an induced current in a conductor is in a
direction such that the applied mechanical force is opposed.
Limit Switch. A device that automatically cuts the power off at or
near the limit of travel of a mechanical member.
Load. The load on an ac machine or apparatus is equal to the product
of the rms voltage across its terminals and the rms current
Locking Relay. A relay that operates to make some other device
inoperative under certain conditions.
Loom. See Tubing, Flexible.
Luminosity. Relative quantity of light.
Magnet. A magnet is a body that is the source of a magnetic field.
Magnetic Field. A magnetic field is the space containing distributed
energy in the vicinity of a magnet and in which magnetic forces
are apparent.
Magnetizing Force. Number of ampere-turns in a transformer primary
per unit length of core.
Magnetomotive Force. Number of ampere-turns in a transformer
Mass. Quantity of matter; the physical property that determines the
acceleration of a body as the result of an applied force.
Glossary 429
Matter. Matter is a physical entity that exhibits mass.
Meter. A unit of length equal to 39.37 inches; also, an electrical
instrument for measurement of voltage, current, power, energy,
phase angle, synchronism, resistance, reactance, impedance, inductance,
capacitance, and so on.
Mho. The unit of conductance defined as the reciprocal of the ohm.
Mounting, Circuit Breaker. Supporting structure for a circuit
Multiple Feeder. Two or more feeders connected in parallel.
Multiple Joint. A joint for connecting a branch conductor or cable
to a main conductor or cable to provide a branch circuit.
Multiplier, Instrument. A series resistor connected to a meter mechanism
for the purpose of providing a higher voltage-indicating
Mutual Inductance. An inductance common to the primary and secondary
of a transformer, resulting from primary magnetic flux
that cuts the secondary winding.
Negative. A value less than zero; an electric polarity sign indicating
an excess of electrons at one point with respect to another
point; a current sign indicating charge flow away from a
Network. A system of interconnected paths for charge flow.
Network, Active. A network that contains one or more sources of
electrical energy.
Network, Passive. A network that does not contain a source of electrical
No-Load Current. The current demand of a transformer primary
when no current demand is made on the secondary.
Normally Closed. Denotes the automatic closure of contacts in a
relay when deenergized (not applicable to a latching relay).
Normally Open. Denotes the automatic opening of contacts in a
relay when deenergized (not applicable to a latching relay).
Ohm. The unit of resistance; a resistance of one ohm sustains a current
of one ampere when one volt is applied across the resistance.
Ohmmeter. An instrument for measuring resistance values.
Ohm’s Law. States that current is directly proportional to applied
voltage and inversely proportional to resistance, reactance, or
430 Glossary
Open-Circuit Voltage. The terminal voltage of a source under conditions
of no current demand. The open-circuit voltage has a value
equal to the emf of the source.
Open-Wire Circuit. A circuit constructed from conductors that are
separately supported on insulators.
Oscilloscope. An instrument for displaying the waveforms of ac
Outdoor Transformer. A transformer with weatherproof construction.
Outlet. A point in a wiring system from which current is taken for
supply of fixtures, lamps, heaters, and so on.
Outlet, Lighting. An outlet used for direct connection of a lamp
holder, lighting fixture, or a cord that supplies a lamp holder.
Outlet, Receptacle. An outlet used with one or more receptacles that
are not of the screw-shell type.
Overload Protection. Interruption or reduction of current under
conditions of excessive demand, provided by a protective
Ozone. A compound consisting of three atoms of oxygen, produced
by the action of electric sparks or specialized electrical devices.
Peak Current. The maximum value (crest value) of an alternating
Peak Voltage. The maximum value (crest value) of an alternating
Peak-to-Peak Value. The value of an ac waveform from its positive
peak to its negative peak. In the case of a sine wave, the peak-topeak
value is double the peak value.
Pendant. A fitting suspended from overhead by a flexible cord that
may also provide electrical connection to the fitting.
Pendant, Rise-and-Fall. A pendant that can be adjusted in height by
means of a cord adjuster.
Period. The time required for an ac waveform to complete one cycle.
Permanent Magnet. A magnetized substance that has substantial
Permeability. The ratio of magnetic flux density to magnetizing
Phase. The time of occurrence of the peak value of an ac waveform
with respect to the time of occurrence of the peak value of a
Glossary 431
reference waveform. Phase is usually stated as the fractional part
of a period.
Phase Angle. An angular expression of phase difference; it is commonly
expressed in degrees and is equal to the phase multiplied
by 360◦.
Plug. A device inserted into a receptacle for connection of a cord to
the conductor terminations in the receptacle.
Polarity. An electrical characteristic of emf that determines the direction
in which current tends to flow.
Polarization (Battery). Polarization is caused by development of gas
at the battery electrodes during current demand and has the effect
of increasing the internal resistance of the battery.
Pole. The pole of a magnet is an area at which its flux lines tend to
converge or diverge.
Positive. A value greater than zero; an electric polarity sign denoting
a deficiency of electrons at one point with respect to another point;
a current sign indicating charge flow toward a junction.
Potential Difference. A potential difference of one volt is produced
when one unit of work is done in separating unit charges through
a unit distance.
Potentiometer. A resistor with a continuously variable contact arm;
electrical connections are made to both ends of the resistor and
to the arm.
Power. The rate of doing work, or the rate of converting energy.
When one volt is applied to a load and the current demand is one
ampere, the rate of energy conversion (power) is one watt.
Power, Real. Real power is developed by circuit resistance, or effective
Primary Battery. A battery that cannot be recharged after its chemical
energy has been depleted.
Primary Winding. The input winding of a transformer.
Proton. The subatomic unit of positive charge; a proton has a charge
that is equal and opposite to that of an electron.
Pull Box. Ametal box with a blank cover for insertion into a conduit
run, raceway, or metallic tubing, which facilitates the drawing of
Pulsating Current. A direct current that does not have a steady
432 Glossary
Puncture. A disruptive electrical discharge through insulation.
Quick-Break. A switch or circuit breaker that has a high contactopening
Quick-Make. A switch or circuit breaker that has a high contactclosing
Raceway. A channel for holding wires or cables; constructed from
metal, wood, or plastics, rigid metal conduit, electrical metal
tubing, cast-in-place, underfloor, surface metal, surface wooden
types, wireways, busways, and auxiliary gutters.
Rack, Cable. A device secured to the wall to provide support for a
cable raceway.
Rating. The rating of a device, apparatus, or machine states the limit
or limits of its operating characteristics. Ratings are commonly
stated in volt, amperes, watts, ohms, degrees, horsepower, and so
Reactance. Reactance is an opposition to ac current based on the
reaction of energy storage, either as a magnetic field or as an electric
field. No real power is dissipated by a reactance. Reactance
is measured in ohms.
Reactor. An inductor or a capacitor. Reactors serve as currentlimiting
devices such as in motor starters, for phase-shifting applications
as in capacitor start motors, and for power-factor correction
in factories or shops.
Receptacle. Also termed convenience outlet; a contacting device installed
at an outlet for connection externally by means of a plug
and flexible cord.
Rectifier. A device that has a high resistance in one direction and a
low resistance in the other direction.
Regulation. Denotes the extent to which the terminal voltage of a
battery, generator, or other source decreases under current demand.
Commonly expressed as the ratio of the difference of the
no-load voltage and the load voltage to the no-load voltage under
rated current demand; usually expressed as a percentage.
Relay. A device operated by a change in voltage or current in a circuit,
which actuates other devices in the same circuit or in another
Reluctance. An opposition to the establishment of magnetic flux
lines when a magnetizing force is applied; usually measured in
Glossary 433
Remanence. The flux density that remains in a magnetic substance
after an applied magnetomotive force has been removed.
Resistance. A physical property that opposes current and dissipates
real power in the form of heat. Resistance is measured in
Resistor. A positive component; may be wire-wound, carboncomposition,
thyrite, or other design.
Rheostat. A variable resistive device consisting of a resistance element
and a continuously adjustable contact arm.
Rosette. A porcelain or other enclosure with terminals for connecting
a flexible cord and pendant to the permanent wiring.
Safety Outlet. Also termed ground outlet; an outlet with a polarized
receptacle for equipment grounding.
Secondary Battery. Abattery that can be recharged after its chemical
energy is depleted.
Sequence Switch. A remotely controlled power-operated switching
Series Circuit. A circuit that provides a complete path for current
and has its components connected end-to-end.
Service. The conductors and equipment for supplying electrical energy
from the main or feeder or from the transformer to the area
Serving, of Cable. A wrapping over the core of a cable before it is
leaded or over the lead if it is armored.
Shaded Pole. A single heavy conducting loop placed around one half
of a magnetic pole that develops an ac field, in order to induce an
out-of-phase magnetic field.
Sheath, Cable. A protective covering (usually lead) applied to a
Shell Core. A core for a transformer or reactor consisting of three
legs, with the winding located on the center leg.
Short Circuit. A fault path for current in a circuit that conducts
excessive current; if the fault path has appreciable resistance, it is
termed a leakage path.
Shunt. Denotes a parallel connection.
Sine Wave. Variation in accordance with simple harmonic motion.
Sinusoidal. Having the form of a sine wave.
434 Glossary
Sleeve, Splicing. Also termed connector; a metal sleeve (usually
copper) slipped over and secured to the butted ends of conductors
to make a joint that provides good electrical connection.
Sleeve Wire. A circuit conductor connected to the sleeve of a plug
or jack.
Sliding Contact. An adjustable contact arranged to slide mechanically
over a resistive element, over turns of a reactor, over series
of taps, or around the turns of a helix.
Snake. A steel wire or flat ribbon with a hook at one end, used to
draw wires through conduit, et cetera.
Socket. A device for mechanical support of a device (such as a lamp)
and for connection to the electrical supply.
Solderless Connector. Any device that connects wires together without
solder; wire nuts are the most common type.
Solenoid. A conducting helix with a comparatively small pitch; also
applied to coaxial conducting helices.
Spark Coil. Also termed ignition coil; a step-up transformer designed
to operate from a dc source via an interrupter that alternately
makes and breaks the primary circuit.
Sparkover. A disruptive electrical discharge between the electrodes
of a gap; generally used with reference to measurement of highvoltage
values with a gap having specified types and shape of
Splice. Also termed straight-through joint; a series connection of a
pair of conductors or cables.
Standard Cell. A highly precise source of dc voltage, also called a
Weston cell; standard cells are used to check voltmeter calibration
and for highly precise measurement of dc voltage values.
Station, Automatic. A generating station or substation that is usually
unattended and performs its intended functions by an automatic
Surge. A transient variation in current and/or voltage at a given
point in a circuit.
Switch. A device for making, breaking, or rearranging the connections
of an electric circuit.
Symbol. A graphical representation of a circuit component; also, a
letter or letters used to represent a component, electrical property,
or circuit characteristic.
Glossary 435
Tap. In a wiring installation, a T joint (Tee joint),Yjoint, or multiple
joint. Taps are made to resistors, inductors, transformers, and so
Terminal. The terminating end(s) of an electrical device, source, or
circuit, usually supplied with electrical connectors such as terminal
screws, binding posts, tip jacks, snap connectors, or soldering
Three-Phase System. An ac system in which three sources energize
three conductors, each of which provide a voltage that is 120◦ out
of phase with the voltage in the adjacent conductor.
Tie Feeder. A feeder connected at both ends to sources of electrical
energy. In an automatic station, a load may be connected between
the two sources.
Time Delay. A specified period of time from the actuation of a control
device to its operation of another device or circuit.
Tip, Plug. The contacting member at the end of a plug.
Torque. Mechanical twisting force.
Transfer Box. Also termed pull box; a box without a distribution
panel containing branched or otherwise interconnected
Transformer. A device that operates by electromagnetic induction
with a tapped winding, or two or more separate windings,
usually on an iron core, for the purpose of stepping voltage
or current up or down, for maximum power transfer, for isolation
of the primary circuit from the secondary circuit, and
in special designs for automatic regulation of voltage or
Transient. A nonrepetitive or arbitrarily timed electrical surge.
Transmission (AC). Transfer of electrical energy from a source to a
load or to one or more stations for subsequent distribution.
Troughing. An open earthenware channel, wood, or plastic in which
cables are installed under a protective cover.
Tubing, Electrical Metal(lic) (EMT). A thin-walled steel raceway of
circular form with a corrosion-resistant coating for protection of
wire or cables.
Tubing, Flexible. Also termed loom; a mechanical protection for
electrical conductors; a flame-resistant and moisture-repellent circular
tube of fibrous material.
436 Glossary
Twin Cable. A cable consisting of two insulating and stranded conductors
arranged in parallel runs and having a common insulating
Underground Cable. A cable designed for installation below the
surface of the ground or for installation in an underground
Undergrounded System. Also termed insulated supply system; an
electrical system that floats above ground, or one that has only a
very high impedance conducting path to ground.
Unidirectional Current. A direct current or a pulsating direct current.
Units. Established values of physical properties used in measurement
and calculation; for example, the volt unit, the ampere unit,
the ampere-turn unit, the ohms unit.
Value. The magnitude of a physical property expressed in terms of
a reference unit, such as 117 volts, 60 Hz, 50 ohms, 3 henrys.
VAR. Denotes volt-amperes reactive; the unit of imaginary power
(reactive power).
Variable Component. A component that has a continuously controllable
value, such as a rheostat or movable-core inductor.
Vector. A graphical symbol for an alternating voltage or current,
the length of which denotes the amplitude of the voltage or current,
and the angle of which denotes the phase with respect to a
reference phase.
Ventilated. A ventilated component is provided with means of air
circulation for removal of heat, fumes, vapors, and so on.
Vibrator. An electromechanical device that changes direct current
into pulsating direct current (direct current with an ac component).
Volt. The unit of emf; one volt produces a current of one ampere in
a resistance of one ohm.
Voltage. In a circuit, the greatest effective potential difference between
a specified pair of circuit conductors.
Voltmeter. An instrument for measurement of voltage values.
Watt. The unit of electrical power, equal to the product of one volt
and one ampere in dc values, or in rms ac values.
Watt-hour. A unit of electrical energy, equal to one watt operating
for one hour.
Glossary 437
Wattmeter. An instrument for measurement of electrical power.
Wave. An electrical undulation, basically of sinusoidal form.
Weatherproof. A conductor or device designed so that water, wind,
or usual vapors will not impair its operation.
Wind Bracing. A system of bracing for securing the position of conductors
or their supports to avoid the possibility of contact due
to deflection by wind forces.
Wiper. An electrical contact arm.
Wire Nut. The most commonly used type of solderless connector.
Work. The product of force and the distance through which the
force acts; work is numerically equal to energy.
Working Voltage. Also termed closed-circuit voltage; the terminal
voltage of a source of electricity under a specified current demand;
also, the rated voltage of an electrical component such as
a capacitor.
X Ray. An electromagnetic radiation with extremely short wavelength,
capable of penetrating solid substances; used in industrial
plants to check the perfection of device and component fabrication
(detection of flaws).
Y Joint. A branch joint used to connect a conductor to a main conductor
or cable for providing a branched current path.
Y Section. Also termed T section; an arrangement of three resistors,
reactors, or impedances that are connected together at one end of
each, with their other ends connected to individual circuits.
Zero-Adjuster. A machine screw provided under the window of a
meter for bringing the pointer exactly to the zero mark on the
Zero-Voltage Level. A horizontal line drawn through a waveform to
indicate where the positive excursion falls to zero value, followed
by the negative excursion. In a sine wave, the zero-voltage level is
located halfway between the positive peak and the negative peak.

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