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Basic Electrical Terms

Basic Electrical Terms

Volt - the unit of electromotive force, the measure of electrical pressure, is abbreviated v or V, and voltage is represented by I. The voltage (of a circuit) is the effective (greatest root-mean-square) difference of potential between any two conductors of the circuit concerned. Some systems, such as 3-phase 4-wire and single-phase 3-wire may have multiple circuits of differing voltages. The Nominal Voltage is the value assigned to a circuit to conveniently designate its voltage class (e.g. 120 volts, 240 volts, 480 volts). The actual voltage of the circuit can vary.

Amp - or Ampere, the unit of intensity of electrical current (the measure of electrical flow), is abbreviated a or A.

Watt - the unit of power or rate of work represented by a current of one ampere under a pressure of one volt (abbreviated w or W). The English horsepower is approximately equal to 846 watts. Wattage ratings of lamps actually measure the power consumption not the illuminating capability.

Service - the conductors and equipment for delivering electrical energy from the supply system (e.g. the electric power utility) to the wiring system of the premises served.

Ohm - the unit of electrical resistance and impedance, abbreviated with the symbol omega, W. Resistance is the opposition offered by a substance to the passage of electrical current. Impedance is the apparent resistance in a circuit to the flow of alternating current.Kilowatt-hour - Work done at the steady rate equivalent to 1000 watts in one hour. Power utility companies base their billing upon the number of kilowatt-hours (KWH) consumed.

Ohm's Law - A statement of the relationship, discovered by the German scientist G. S. Ohm, between the voltage, amperage and resistance of a circuit. It states the voltage of a circuit in volts is equal to the product of the amperage in amperes and the resistance in ohms.


Transformer - An apparatus for converting an alternating electrical current from a high to a low potential (voltage) or vice versa. Uses of transformers include but are not limited to the conversion of utility transmission voltage to the voltage of the premises wiring system and conversion of of voltage for use with chimes, alarm systems and low-voltage lighting. Transformers can also be used to compensate for minor variations equipment voltage requirements. Transformers only change voltage and amperage.

GFCI (Ground Fault Circuit Interrupter) - A device intended for the protection of personnel that de-energizes a circuit or portion of a circuit when the current to ground exceeds a preset value. "Ground Fault" is the name applied to this undesired circuit condition. In dwelling units (e.g. houses, apartments), GFCI protection is currently required in bathrooms, garages, outdoors, unfinished basements, kitchens and wet bar sinks. Other specific installations and/or areas may also necessitate the need for protection

Single Phase - a system of alternating current power where the phase relationship between ungrounded conductors is either 0 or 10 degrees.

Three Phase - a system of alternating current power where the phase relationship between ungrounded conductors is either 0 or 120 degrees.

NEC (National Electrical Code) - a document produced by the National Fire Protection Association for the purpose of the practical safeguarding of persons and property from hazards arising from the use of electricity. Authorities having legal jurisdiction over electrical installations adopt the code for mandatory application ( i.e. incorporate the code into law).

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 damaging itself when operated according to its rating.

Fuse - An over current protective device with a circuit opening part that is heated and broken by the passage of an over current through it.

Listed - Equipment and/or materials included in a list published by an organization concerned with product evaluation and production of listed items. The listing states whether the item meets designated standards or is suitable for use in a specified manner. Listing organizations acceptable to jurisdiction authorities include Underwriters' Laboratories (UL) and CSA.

Accessible - Three common uses of accessible:

  • (wiring methods) - Capable of being removed or exposed without damaging the building structure of finish, or not permanently enclosed by such. Wires in concealed raceways are not considered accessible.

  • (equipment) -Admitting close approach; not guarded by locked doors or other effective means. See readily accessible below.

  • Readily Accessible - Capable of being reached quickly for operation, renewal, or inspections without the requirement of climbing over or removing obstacles or use of portable ladders, chairs, etc.

Labeled - Equipment or materials that a label or other identifying mark of a listing organization has been attached.

Overload - Operation in excess of normal full-load rating or rated ampacity which could cause damage or dangerous overheating if continued for a sufficient time. A fault, such as a short circuit or ground fault, is not an overload. See "Over Current".

Over current - Any current in excess of the rated current or ampacity. It may result from overload, short circuit or ground fault.

Raceway - An enclosed channel of metallic or nonmetallic materials designed expressly for holding wires, cables, or bussbars. Examples are electrical metallic tubing (EMT), flexible metallic tubing and nonmetallic rigid conduit.

Ground - A conducting connection, intentional or accidental, between an electrical circuit or equipment and the earth, or some conducting body that serves in place of the earth. Other associated terms are:

  • Grounded conductor - A system or circuit conductor that is intentionally connected to ground. This conductor has also been referred to as the neutral or common conductor.

  • Grounding conductor - a conductor used to connect equipment or the grounded circuit of a wiring system to the grounding electrode (s).

  • Ungrounded conductor - A current carrying conductor not connected to ground.

Device - A unit of an electrical system that is intended to carry but not utilize electricity.

  • Receptacle - a device installed for the connection of a single contact device. Receptacles provide a means of connecting apparatus that utilize electricity to the wiring system.

Box - An enclosure designed to provide access to the electrical wiring system. Uses include but are not limited to provide device and lighting outlets and wiring system junction points. Specially designed boxes are required for the support of listed ceiling fans weighing less than 35 lb (15. kg). Fans exceeding this weight limit must be supported independently of the outlet box.

Circuit - A complete path from the energy source through conducting bodies and back to the energy source. For example:

Conductor - a substance or body capable of transmitting electricity.

  • Bare - A conductor having no covering or electrical insulation whatsoever.

  • Covered - A conductor encased within material of composition or thickness that is not recognized by the NEC as electrical insulation.

  • Insulated - A conductor encased within material of composition or thickness that is recognized by the NEC as electrical insulation.

Equipment - A general term including material, fittings, devices, alliances, fixtures, apparatus , and similar items used as a part of, or in connection with, an electrical installation.

Lamp - A general term for various devices for artificially producing light including commonly called items such as light bulbs and fluorescent tubes.

AC and DC - Abbreviations for alternating current and direct current respectively.

  • Current - a movement of electricity analogous to the flow of a stream of water.

  • Direct Current - An electric current flowing in one direction only (i.e. current produced using a battery).

  • Alternating Current - a periodic electric current that reverses its direction at regular intervals.

  • Phase

    • the point or stage in the period to which the rotation, oscillation, or variation has advanced relative to a standard position or starting point.

    • electrically, one of the voltage sources of an alternating current electrical system whose voltage state is measured relative to a standard point.


Many of the definitions used are based on information contained in the National Electrical Code published by the National Fire Protection Association and Webster's New World Dictionary.


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