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