UL / ULC - Underwriters™ Laboratories is an independent, not-for-profit, nongovernmental product safety organization responsible for product safety standards development, testing, and certification.
Underwriters' Laboratories USA / Underwriters' Laboratories of Canada

Underfloor Raceway - A raceway suitable for use in the floor.

Universal Taps - A combination of six primary voltage taps consisting of four 2-1/2% FCBN and two 2-1/2: FCAN, covering 15% voltage range (also see definition for Tap).

USASSI - United States of America Standards Institute (previously ASA; now ANSI).

Utilization Equipment - Equipment which utilizes electrical energy for mechanical, chemical, heating, lighting, or similar useful purposes.

Varistor - A two-electrode semiconductor device with a voltage dependent on nonlinear resistance that drops markedly as the applied voltage is increased.

Varying Duty - see definition for Duty.

Vault (transformer vault or electrical equipment vault) - An isolated enclosure, either above or below ground, with fire-resisting walls, ceilings, and floors for the purpose of housing transformers and other electrical equipment.

Vent - An intentional opening for the escape of gasses to the outside.

Ventilated Cable Tray - see definition for Cable Tray.

Vessel - Any ship or boat or any other description of vessel used or designed to be used in navigation

Volt (V) - The unit of measure for voltage.

Volt-Amperes (VA) - The current flowing in a circuit multiplied by the voltage of that circuit. An expression of the output rating of a transformer.

Voltage - Electric pressure; the force which causes current to flow through an electrical conductor.

High Voltage - Any voltage above 750 V.

Low Voltage - Any voltage from 31 to 750 V inclusive.

Extra-Low-Voltage - Any voltage up to and including 30 V.

Step Voltage - the potential difference between two points on the earth’s surface separated by a distance of one pace, assumed to be 1 m in the direction of maximum voltage gradient.

Touch Voltage - the potential difference between a grounded metal structure and a point on the earth’s surface separated by a distance equal to normal maximum horizontal reach.

Voltage of a Circuit - The greatest root-mean-square (effective) voltage between any two conductors of the circuit concerned.

Voltage-to-Ground - The voltage between any given live ungrounded part and any grounded part in the case of grounded circuits, or the greatest voltage existing in the circuit in the case of ungrounded circuits.

Voltage Regulation - For a transformer, the change in secondary voltage which occurs when the load is reduced from rated value to zero, with the values of all other quantities remaining unchanged. The regulation may be expressed in percent (or per unit) on the basis of the rated secondary voltage at full load.

Voltage Regulator - An electrical device on an electric system that keeps voltage which is supplied to customers at a constant level, usually around 120 volts, regardless of load fluctuations.

Washroom - A room containing a wash basin(s) and may contain a water closet(s) but without bathing or showering facilities.

Waveshape Designation - The wave shape of an impluse (other than rectangular) of a current or voltage is designated by a combination of two numbers. The first, an index of the wave front, is the virtual duration of the wave front in microseconds. The second, an index of the wave tail, is the time in microseconds from the virtual zero to the instant at which one-half of the crest value is reached on the wave tail. Examples are 1.2/50 and 8/20 microsecond wave' the wave shape of a rectangular impulse of current or voltage is designated by two numbers. The first designates the minimum value of the current of voltage that is sustained for the time in microseconds designated by the second number. An example is 75 A, 2000 microsecond wave.

Weatherproof - A device constructed so that exposure to weather will not interfere with successful operation.

Wet Location - see definition for Location.

Withstand Voltage - The highest value of applied voltage at which equipment will not flash over.

Wire Connector - see definition for Connector.

Wireway - A raceway consisting of a completely enclosing arrangement of metal troughing, and fittings therefore, so formed and constructed that insulated conductors may be readily drawn in and withdrawn, or laid in and removed, after the wireway has been completely installed, without injury either to conductors or their covering.

Wye Connection - A three-phase connection in which similar ends of each phase winding are connected together at a common point which forms the electrical neutral and is often grounded.