Electrical Definitions


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Electrical Definitions

Letter - A

Accent Lighting

Directional lighting to emphasize a particular object or draw attention to a part of the field of view.



(as applied to equipment) Admitting close approach: not guarded by locked doors, elevation, or other effective means. (see Accessible, Readily)



(As applied to wiring methods) Capable of being removed or exposed without damaging the building structure or finish, or not permanently closed in by the structure or finish of the building.


Accessible, Readily

(Readily Accessible) Capable of being reached quickly for operation, renewal, or inspections, without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, chairs, etc.



Mechanical part of a limit switch that uses mechanical force to actuate the switch contacts.


Alternating Current

(AC)- A current which periodically changes its direction.


Alternating Voltage

A voltage which periodically changes its polarity.



One-half of a cycle, consisting of the complete rise and fall of an alternating voltage or current in one direction.



An alternating current generator.


Ambient Temperature

The temperature of the air, water, or surrounding earth. Conductor ampacity is corrected for changes in ambient temperature including temperatures below 86F. The cooling effect can increase the current carrying capacity of the conductor. (Review Section 310-10 of the Electrical Code for more understanding)



An electric meter used to measure current, calibrated in amperes.



The unit of electrical current. (See Ampere)



The current-carrying capacity of conductors or equipment, expressed in amperes.



The basic unit measuring the quantity of electricity. The unit of current flow. Represented by I.


Ampere-Hour Capacity

The quantity of electricity measured in ampere-hours (Ah) which may be delivered by a cell or battery under specified conditions.


Ampere-Hour Efficiency

The ratio of the output of a secondary cell or battery, measured in ampere-hours, to the input required to restore the initial state of charge, under specified conditions (also coulombic efficiency).



Procedure of expanding the strength of a signal.



A device use to increase the strength of a signal.



The maximum value of a wave.



In a diode, the electrode that must be positive with respect to the cathode to allow the diode to conduct. The plate of an electron tube.



Utilization equipment, generally other than industrial, normally built in standardized sizes or types, which is installed or connected as a unit to perform one or more functions.



Sparking that results when undesirable current flows between two points of differing potential. This may be due to leakage through the intermediate insulation or a leakage path due to contamination.



A device that employs the deionization principle to confine and extinguish an arc.


Arc-Fault Circuit Interrupter

A device designed to provide protection from the effects of rapid current fluctuations due to arcing conditions.



That part of an electric generator in which the voltage is induced.


Armature Coil

A winding that develops current output from a generator when its turns cut a magnetic flux.


Armored Cable

Cable with a metal sheathing.



A nonlinear device to limit the amplitude of voltage on a power line. The term implies that the device stops overvoltage problems (i.e. lightning). In actuality, voltage clamp levels, response times and installation determine how much voltage can be removed by the operation of an arrester.



Unequal distribution about one or more axes.


Attachment Plug

(Plug cap) (Cap). A device which, by insertion in a receptacle, establishes connection between the conductors of the attached flexible cord and the conductors connected permanently to the receptacle.



The reduction of a signal from one point to another. For an electrical surge, attenuation refers to the reduction of an incoming surge by a limiter (attenuator). Wire resistance, arresters, power conditioners attenuate surges to varying degrees.



A device that reduces signal power.


Authority Having Jurisdiction (AHJ)

A governing body that has the authority to enforce rules, regulations, codes, and standards for electrical installations.



Self-acting, operating by its own mechanism when actuated by some impersonal influence, as for example, a change in current strength, pressure, temperature, or mechanical configuration.



A transformer used to step voltage up or down. The primary and secondary windings share common turns, and it provides no isolation.


Auxiliary Contracts

Subordinate contacts which operate with the movement of the main contracts.


Auxiliary Source

A power source dedicated to providing emergency power to a critical load when commercial power is interrupted.



American Wire Gage. This term refers to the U.S. standard for wire size.