Electrical Terms for Exams: Key Concepts and Definitions

Admittance

The reciprocal of impedance.

Alternating Current

A periodic current, the average value of which over a period is zero.

Alternator (Synchronous Generator)

A synchronous alternating-current machine that changes mechanical power into electrical power.

Ammeter

An instrument for measuring electric current.

Ampacity

The current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

Ampere

A charge flow of one coulomb per second.

Autotransformer

A transformer in which part of the winding is common to both the primary and secondary circuits; output voltage adjusts automatically depending on required voltage of utilization equipment.

Ballast

A device used with fluorescent and high-intensity discharge lamps to provide the necessary circuit condition for starting and operating the lamp.

Branch Circuit

The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

Busbar

A metallic bar used to provide common contact or termination for a group of all wires or cables such as in an auxiliary gutter, panelboard or a switchboard assembly.

Circuit Breaker

A device designed to open and close a circuit by non-automatic means and to open the circuit automatically on a predetermined over-current without damage to itself when properly applied within its rating.

Conductance

A measure of permissiveness to charge flow; the reciprocal of resistance.

Conductivity

A measure of the ability of a material or substance to conduct electric current, equal to the reciprocal of the resistivity of the substance.

Conductor

A substance that has free electrons or other charge carriers which permit charge flow when an emf (electromotive force) is applied across the substance.

Conduit

A duct or tube for enclosing wires or cables; commonly formed from iron pipe or plastic tubing.

Conduit Fittings

Accessories used to complete a conduit system, such as boxes, bushings and access fitting.

Condulet

A device installed at intermediate points usually at turns to facilitate easy pull through of wires and provide junction of wires for splicing; usually provided with an access cover.

Convenience Outlet

An outlet which receives the plug with flexible cord of electrical appliances or equipment such as lamps, refrigerator, television set, power tools, etc.

Coulomb

An electric charge of 6.28 x 10^18 electrons. One coulomb is transferred when a current of 1 ampere continues past a point for 1 second.

Current

The rate of charge flow. A current of 1 ampere is equal to a flow rate of 1 coulomb per second.

Demand Factor

The ratio of the maximum demand of a system, or part of a system, to the total connected load of a system or part of the system under consideration.

Direct Current

A unidirectional current with a constant value.

Disconnecting Means

A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.

Distribution Center

A point at which energy is divided among feeders or branch or combination of both, and where overcurrent devices are usually located.

Electric Circuit

A conducting path through which electric charges may flow.

Electric Motor

A device for converting electrical energy into mechanical energy.

Electrical Surge

A transient wave of current, potential or power in the electric circuit.

Electromagnetic Induction

A process of emf (electromotive force) generation induced by movement of magnetic flux which cuts an electrical conductor; used in generators to produce current.

Electromotive Force (EMF)

An energy-charge relation that results in electric pressure, which produces or tends to produce charge flow.

Farad

A unit of capacitance defined by the production of one volt across the capacitor terminals when a charge of one coulomb is stored.

Feeder

All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit over-current device.

Flexible Conduit

Non-rigid metallic or non-metallic conduit into which conductors may be drawn.

Frequency

The number of periods occurring in unit time of a periodic process such as in the flow of electric charge.

Fuse

A protective device with a fusible element that opens the circuit by melting when subjected to excessive current.

Generator

A machine that converts mechanical energy into electrical energy utilizing electromagnetic induction principle.

Ground

A conducting connection, whether intentional or accidental, between an electric circuit or equipment and the earth, or to some conducting body that serves in place of the earth.

Ground-Fault Circuit Interrupter (GFCI)

A device installed in circuits where current leakage can be especially dangerous.

Grounded Circuit

A circuit in which one conductor or point is intentionally grounded.

Grounded Conductor

A system or circuit conductor that is intentionally grounded.

Grounding Conductor

A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.

Henry

A unit of inductance; it permits current increase at the rate of 1 ampere per second when 1 volt is applied across the inductor terminals.

Impedance

Opposition to AC current by a combination of resistance and reactance; impedance is measured in ohms.

Insulated

Separated from other conducting surfaces by dielectric permanently offering high resistance to the passage of current and to disruptive discharge.

Insulator

A material or substance that does not allow the flow of electricity through it.

Interrupting Rating

The highest current rating at rated voltage that a device is intended to interrupt under standard test conditions.

Inverter

A device that converts direct current (dc) to alternating current (ac).

Isolating Switch

A switch intended for isolating an electrical circuit from the source of power.

Junction Box

A box with a blank cover which serves the purpose of joining different runs of raceway or cable.

Kilowatt-hour

A unit of energy, equal to the energy transferred or expended by one kilowatt in one hour.

Kilowatt-hour Meter

An instrument or device used to measure power consumption measured in kilowatt-hours.

Lighting Outlet

An outlet used for direct connection of a lampholder, lighting fixture, or a cord that supplies a lampholder.

Lightning Arrestor

A device for providing path by which lightning disturbances or other static discharges are passed to earth.

Maximum Demand

Maximum demand of an installation or system is the largest of all the demands which have occurred during the specified period of time.

Meter Center

A point or a place where all meters in a building may be located.

Mho

The unit of conductance defined as the reciprocal of the ohm.

Motor

A device that converts electrical energy into mechanical energy, as an induction motor.

Ohm

The unit of resistance; a resistance of one ohm sustains a current of 1 ampere when 1 volt is applied across the resistance.

Ohm's Law

A law stating that current is directly proportional to the applied voltage and inversely proportional to resistance, reactance or impedance.

Ohmmeter

An instrument for measuring resistance values.

Outlet

A point in a wiring system from which current is taken for supply of fixtures, lamps, heaters, etc.

Overcurrent

Any current in excess of the rated current of the equipment or the ampacity of the conductor.

Overload

Operation of equipment in excess of normal, full load rating, or of a conductor in excess of rated ampacity.

Panelboard

A single or group of panel units designed for assembly in the form of a single panel.

Potential Difference

A potential difference of 1 volt is produced when 1 unit of work is done in separating unit charges through unit distance.

Power

The rate of doing work, or rate of converting energy.

Raceway

A channel for holding wires or cables.

Rated Voltage

The rated voltage of equipment is the voltage to which operating and performance characteristics are referred.

Receptacle

A receptacle is a contact device installed at the outlet for the connection of an attachment plug.

Rectifier

A device that converts alternating current (ac) to direct current (dc).

Resistance

A physical property that opposes current and dissipates real power in the form of heat. Resistance is measured in ohms.

Resistor

A device designed to introduce resistance into an electric circuit.

Series Circuit

A circuit that provides a complete path for current and has its components connected end-to-end.

Service Equipment

The necessary equipment intended to constitute the main control and cutoff of the supply.

Standby Generator

A generator for providing emergency power during power outage; sometimes called Emergency Generator.

Surge Arrester

A protective device for limiting surge voltage on equipment by discharging or bypassing surge current.

Switch

A device for making, breaking, or rearranging the connections of an electric circuit.

Switchboard

A large single panel, frame or assembly of panels on which are mounted switches, over-current and other protective devices.

Transformer

A static alternating current (ac) device used to change voltage by increasing or reducing it.

Uninterruptible Power Supply

An emergency system designed to provide power automatically and instantaneously upon failure of the normal power supply.

Volt

The unit of emf (Electromotive Force); 1 volt produces a current of 1 ampere in a resistance of 1 ohm.

Voltage Drop

The drop in electric pressure in a circuit due to resistance of the conductor.

Watt

The unit of electrical power, equal to the product of 1 volt and 1 ampere in DC values, or in rms AC values.