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Electrical Glossary

Common Electrical Terms, Tools & Techniques

Please use our electrical glossary to answer all of your electrical term or lingo questions. If you're in need of electrical services in Farmington Hills or the surrounding areas, we're only a phone call away at (248) 600-5048, or fill out an online contact form to schedule an appointment with an electrician.

Alternating Current (AC): Electric current, which changes direction with a regular frequency. Domestic mains in the UK have a frequency of 50 Hertz.

Ambient Temperature: The surrounding temperature of an area.

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

Ampere: A type of 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. Named after French physicist Andre M. Ampère in 1836.

Annual Fuel Utilization Efficiency (AFUE): An indication of how well a furnace converts energy into usable heat. The rating is expressed as a percentage of the annual output of heat to the annual energy input to the furnace.

Appliance: Utilization equipment—generally other than industrial and normally built in standardized sizes or types—that is installed or connected as a unit to perform one or more functions such as clothes washing, air conditioning, food mixing, deep frying, etc.

Battery: A group of two or more cells connected together to provide electrical current. Sometimes also used to describe a single cell that converts chemical energy to electrical current.


Brownout: A reduction in voltage and/or power when demand for electricity exceeds generating capacity. The term brownout is misleading because customers generally do not notice the reduction except when it affects sensitive electronic equipment.

BTU (British thermal unit): A BTU is the standard unit for measuring the quantity of heat energy such as the heat content of fuel. It is the amount of heat energy necessary to raise the temperature of one pound of water one degree Fahrenheit (3412 BTU's=1 kWh).

Capacitor: A device that stores electrical charge usually by means of conducting plates or foil separated by a thin insulating layer of dielectric material. The effectiveness of the device, or its capacitance, is measured in Farads.

Circuit Breaker: A device designed to open and close a circuit by non-automatic means and to open the circuit automatically on a pre-determined overcurrent without damage to itself when properly applied within its rating.




  • Bare: A conductor having no covering or electrical insulation whatsoever.
  • Covered: A conductor encased within material of composition and thickness that is NOT recognized by this code as electrical insulation.
  • Insulated: A conductor encased within material of composition and thickness that is recognized by this code as electrical insulation.

Current: The flow of electricity commonly measured in amperes.

Decibel: A logarithmic measure of the ratio of two quantities, abbreviated dB. For electrical power, 1 dB = 10 x log10 P1/P2. For electric voltage or current, 1 dB = 20 x log10 E1/E2.

Electric Resistance Heating: A type of heating system that generates heat by passing current through a conductor, causing it to heat up. These systems usually use baseboard heaters, often with individual controls. They are inefficient and are best used as a backup to more efficient options, such as solar heating or a heat pump.

Electronic Ballasts: An electronic device that regulates the voltage of fluorescent lamps. Compared to older magnetic ballasts, electronic ballasts use less electricity and are not prone to the flickering and humming effects sometimes associated with magnetic ballasts.


Energizing: Electrically connected to a source of potential difference.

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

Energy Efficiency Ratio (EER): The ratio of the cooling capacity of the air conditioner, in Btu per hour, to the total electrical input in watts under test conditions specified by the Air-Conditioning and Refrigeration Institute.


Equipment: A general term including materials, fittings, devices, appliances, fixtures, apparatus, and the like used as a part of, or in connection with, an electrical installation.

Fault: A short circuit in an electrical system.

Fluorescent Lamps: Fluorescent lamps produce light by passing electricity through a gas, causing it to glow. The gas produces ultraviolet light; a phosphor coating on the inside of the lamp absorbs the ultraviolet light and produces visible light. Fluorescent lamps produce much less heat than incandescent lamps and are more energy efficient. Linear fluorescent lamps are used in long narrow fixtures designed for such lamps. Compact fluorescent light bulbs have been designed to replace incandescent light bulbs in table lamps, floodlights, and other fixtures.

Generator: A rotating machine that converts mechanical energy into electrical energy. In the automotive industry, traditional terminology uses generator to refer to only those machines designed to produce dc current through brushes and a commutator (as opposed to alternator).

Grid: In an electrical system, a term used to refer to the electrical utility distribution network.

Ground (Wire): A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth.



Horsepower: A unit of power equal to 746 watts.

Impedance: The total effects of a circuit that oppose the flow of an AC current consisting of inductance, capacitance, and resistance. It can be quantified in the units of ohms.

Impulse: A current surge.

Incandescent Light Bulbs: Incandescent light bulbs produce light by passing electricity through a thin filament, which becomes hot and glows brightly. Incandescent light bulbs are less energy-efficient than fluorescent lamps because much of the electrical energy is converted to heat instead of light. The heat produced by these bulbs not only wastes energy but can also make a building's air conditioning system work harder and consume more energy.

Infrared Cameras: Energy contractors use infrared cameras to look at the heat leaking into or out of your house. The infrared camera "sees" the heat and can show "hot spots" where a lot of heat is being lost. This helps to identify the places where your home's energy efficiency can be improved.

Insulation: A material having a high resistance to the flow of electric current; insulation over underground conductor is made of either EPR or XLPE material.

Insulator: Any material that does not allow electrons to flow through it.

Interrupter: An element designed to interrupt specific currents under specified conditions.

Inverter: An electrical device that is designed to convert direct current into alternating current. This was originally done with rotating machines which produced true sine wave ac output. More recently, this conversion has been performed more economically and efficiently using solid state electronics. However, except for the most expensive models, these devices usually do not produce perfect sine wave output. This sometimes can result in electromagnetic interference with other sensitive electronic devices.

Joule’s Law: Defines the relationship between current in a wire and the thermal energy produced. In 1841, an English physicist James P. Joule experimentally showed that W = I2 x R x t where I is the current in the wire in amperes, R is the resistance of the wire in Ohms, t is the length of time that the current flows in seconds, and W is the energy produced in Joules.

Kilovolt: A unit of electrical potential equal to 1,000 volts; abbreviated kV or KV.

Kilowatt (kW): Real power delivered to a load (W x 1,000 VA).

Kilowatt-Hour: A unit of energy or work equal to one kilowatt for one hour; abbreviated as kWh or KWH. This is the normal quantity used for metering and billing electricity customers. The price for a kWh varies from approximately 4 cents to 15 cents. At a 100% conversion efficiency, one kWh is equivalent to about 4 fluid ounces of gasoline, 3/16 pound LP, 3 cubic feet natural gas, or 1/4 pound coal.

Limit Switch: A switch that is operated by some part or motion of a power-driven machine or equipment to alter the electric circuit associated with the machine or equipment.

Liquid-Filled Transformer: A transformer in which the core and coil are immersed in a liquid, which acts as both a cooling and insulating medium.

Live Parts: Electric conductors, buses, terminals, or components that are uninsulated or exposed and an electric shock hazard exists.

Load: The load of a transformer is the power, in kVA or volt-amperes, supplied by the transformer.

Load Center: Source for all power to the home; all circuits originate from the "Load Center" or "Service Panel." Circuit breakers are located within this panel.

Load Switching: Transferring the load from one source to another.



National Electrical Code (NEC): A code/guideline used for the safeguarding of people and property from hazards related to the use of electricity. Compliance with this code along with proper maintenance will result in an installation essentially free from hazard; abbreviated NEC. 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: The junction point of the legs in a Wye circuit.

Ohm: The unit of measure for resistance.

Outlet: A point on the wiring system at which current is taken to supply utilization equipment.


Overvoltage: A voltage above the normal rated voltage or the maximum operating voltage of a device or circuit. A direct test overvoltage is a voltage above the peak of the line alternating voltage.

Phase: Classification of an AC circuit usually single-phase, two wire or three wire; two-phase, three wire or four wire; or three-phase, three wire or four wire.

Power: The rate at which work is performed or that energy is transferred. Electric power is commonly measured in watts or kilowatts. A power of 746 watts is equivalent to one horsepower.

Power Outage: An interruption of power.

Power Outlet: An enclosed assembly that may include receptacles, circuit breakers, fuse holders, fused switches, buses, and watt-hour meter mounting means; intended to supply and control power to mobile homes, recreational vehicles, park trailers, or boats; or to serve as a means for distributing power required to operate mobile or temporarily installed equipment.

Qualified Person: One familiar with the construction and operation of the equipment and the hazards involved.

Rainproof: Constructed, protected, or treated so as to prevent rain from interfering with the successful operation of the apparatus under specified test conditions.


Service: The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.

Service Cable: Service conductors made up in the form of a cable.

Smoke and Carbon Dioxide Detectors: Wall and ceiling mounted sensors located throughout the home used to alert occupants of deadly gasses and smoke inside the home.



Systems Capacity: Represents the ability of a system to meet its customers' needs, or meet the electrical demand of its customers. System capacity is provided by generators, transmission lines, distribution networks and load management.

Tap: A connection brought out of the winding at some point between its extremities, usually to permit changing the voltage or current ratio.

Thermostat: A low-voltage electronic switching device that monitors temperatures inside the home and turns on and off the heating or cooling system in the home.

Track and Accent Lighting: Condition-specific lighting that meets special lighting requirements, providing variable lighting degrees of light and may distribute light in multiple directions.


Transformer: A static electrical device, which by electromagnetic induction transfers electrical energy from one circuit to another circuit, usually with changed values of voltage and current in the process.

Transient: A high amplitude, short duration pulse superimposed on the normal voltage.

Vapor Barrier: Also called a vapor retarder, this is a material that retards the movement of water vapor through a building element (such as walls, floors, and ceilings) and prevents metals from corroding and insulation and structural wood from becoming damp.

Ventilated: Provided with a means to permit circulation of air sufficient to remove an excess of heat, fumes, or vapors.

Volt: The electrical potential difference or pressure across a one-ohm resistance carrying a current of one ampere. Named after Italian physicist Count Alessandro Volta in 1745-1827.

Volt Ampere: A unit of apparent power equal to the mathematical product of a circuit voltage and amperes. Here, apparent power is in contrast to real power. On AC systems, the voltage and current will not be in phase if reactive power is being transmitted; usually abbreviated VA.

Watertight: Constructed so that moisture will not enter the enclosure under specified test conditions.

Waterproof: Constructed or protected so that exposure to the weather will not interfere with successful operation.

Watt: A unit of power equal to the rate of work represented by a current of one ampere under a pressure of one volt. Named after the Scottish engineer James Watt, 1819.

Wiring: A distribution network of wire that conducts electricity to receptacles, switches, and appliances throughout a building/home to provide electricity where needed.

Whole-House Fan: A large fan used to ventilate your entire house. This is usually located in the highest ceiling in the house, and vents to the attic or the outside. Although whole-house fans are a good way to draw hot air from the house, you must be careful to cover and insulate them during the winter, when they often continue to draw hot air from people's houses.

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