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Electrical Terms & Definitions

Electrical Terms & Definitions


Alternating Current ( AC ) : an electrical current which reverses direction repeatedly due to a change in voltage which occurs at the same frequency.

American National Standards Institute ( ANSI ) : a private organization that coordinates and/or approves some US standards, particularly those related to the electrical industry.

American Wire Gauge ( AWG ) : a standard measure which represents the size of wire. The larger the number, the smaller the wire .

Ampere : electric current produced by one volt applied across a resistance of one ohm. It is also equal to the flow of one coulomb per second.

Apparent Power: The product of the voltage (in volts) and the current (in amperes). It comprises both active and reactive power. It is measured in “volt-amperes” and often expressed in “kilovolt-amperes” (kVA) or “megavolt-amperes” (MVA).


Baseload Capacity: The generating equipment normally operated to serve loads on an around-the-clock basis.


Branch Circuit : the conductors between the last overcurrent protective device and the outlets or loads.

Btu (British Thermal Unit): A standard unit for measuring the quantity of heat energy equal to the quantity of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit.

Circuit Breaker : a device designed to open a circuit either by manual action or by automatic action when current exceeds a value longer than permitted. A circuit breaker can provide overcurrent protection.

Conductor : usually a metallic substance capable of transmitting electricity with little resistance . The best conductor at normal temperature ranges is silver

Continuous Load : a sustained electrical load current for three hours or more.

Current : the flow of electricity commonly measured in amperes.

Direct Current ( DC ) : electrical current that normally flows in one direction only.

Energy : the capacity for, or the ability to do, mechanical work. Electrical energy is measured in kilowatt-hours for billing purposes.

Energy Efficiency: Refers to programs that are aimed at reducing the energy used by specific end-use devices and systems, typically without affecting the services provided. These programs reduce overall electricity consumption (reported in megawatthours). Such savings are generally achieved by substituting technically more advanced equipment to produce the same level of end-use services.

Fault : a short circuit.

Grid : a term used to refer to the electrical utility distribution network.

Ground : a conducting connection between an electrical circuit or device and the earth.

Inverter : an electrical device which is designed to convert direct current into alternating current. This was originally done with rotating machines which produced true sine wave ac output.

Kilovar : unit of ac reactive power equal to 1000 vars. Abbreviated KVAR.

Kilovolt : unit of electrical potential equal to 1000 volts. Abbreviated KV.

Kilowatt : unit of power equal to 1000 watts. Abbreviated KW.

Listed : an electrical device or material that has been tested by a recognized organization and shown to meet appropriate standards. Many local governmental authorities require that installed electrical products be listed.

Load : a device which consumes electrical power and is connected to a source of electricity.

MCA : Minimum circuit amperes. This is the minimum current rating allowed for the wiring and circuit breaker or fuse protection for the equipment.

National Electrical Code ( NEC ) : a code for the safeguarding of people and property from hazards related to the use of electricity. The NEC was first developed in 1897 as a result of the efforts of various insurance, electrical, architectural, and allied interests. It is sponsored and regularly updated by the National Fire Protection Association.

Neutral : a conductor of an electrical system which usually operates with minimal voltage to ground. Depending on the type of system, it may carry little current or only unbalance current. Systems that have one conductor grounded use the neutral for this purpose.

Open Circuit Voltage : the maximum voltage produced by a power source with no load connected.

Overcurrent : any current beyond the continuous rated current of the conductor or equipment. This may be value slightly above the rating as in the case of an overload, or may be far above the rating as in the case of a short circuit.

Overload : operation of electrical equipment above its normal full-load rating or of a conductor above its rated ampacity. An overload condition will eventually cause dangerous overheating and damage.

Power : the rate at which work is performed or that energy is transferred. Electric power is commonly measured in watts or kilowatts.

Separately Derived System : an electrical system whose power is provided by a stand-alone generator, transformer, or converter and which has no direct electrical connection or ground connection to another source . The NEC contains special grounding and bonding requirements for such systems.

Short Circuit : a low resistance connection unintentionally made between points of an electrical circuit which may result in current flow far above normal levels.

Single-Phase : an ac electric system or load consisting of at least one pair of conductors energized by a single alternating voltage.

Three-Phase : an ac electric system or load consisting of three conductors energized by alternating voltages that are out of phase by one third of a cycle.

Transformer : a device that converts one ac voltage and current to a different voltage and current. Constructed using two or more coils of wire around a common magnetic core. The energy is transferred from one coil, usually considered the primary winding, to the other coil, the secondary winding by means of mutual induction in the magnetic core

Underwriters Laboratories (UL ) : a non-profit organization that was established by the insurance industry to test electrical devices for safety.

Uninterruptible Power Supply ( UPS ) : a device that provides a constant regulated voltage output in spite of interruptions of the normal power supply. It includes filtering circuits and is usually used to feed computers or related equipment which would otherwise shutdown on brief power interruptions.

Volt : The electrical potential difference or pressure across a one ohm resistance carrying a current of one ampere.

Volt Ampere : a unit of apparent power equal to the mathematical product of a circuit voltage and amperes.

Watt : a unit of power equal to the rate of work represented by a current of one ampere under a pressure of one volt.

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