Half Cycle of Current - A half loop of current
having a duration of 0.00833 seconds.
Half Loop of current - The amount of time it
takes the current to go from one zero reference to another.
Harmonic - Sinusoidal component of an arc voltage
that is a multiple of the fundamental wave frequency.
Harmonic Distortion - The presence of harmonics
that change an ac voltage waveform from sinusoidal to complex.
Hazardous Location - Means premises, buildings,
or parts thereof in which there exists the hazard of fire or explosion
due to the fact that:
- Highly flammable gases, flammable volatile liquid
mixtures, or other highly flammable substances are manufactured
or are stored in other than original
- Combustible dust or flyings are likely to be present in quantities
sufficient to produce an explosive or combustible mixture,
or it is impracticable to prevent
such dust or flyings from collecting in or upon motors or other electrical
equipment in such quantities as to produce overheating through normal
radiation being prevented,
or from being deposited upon incandescent lamps.
- Easily ignitible fibres
or materials producing combustible flyings are manufactured,
handled, or used in a free open state.
- Easily ignitible fibres
or materials producing combustible flyings are stored in
bales or containers but are not manufactured
or handled in a free
Hazardous location special terminology:
Cable Gland - a
device or combination of devices intended to provide a means of
entry of a cable or flexible
cord into an enclosure situated in a hazardous location and that
also provides strain relief and shall be permitted
to provide sealing characteristics where required, either by an
integral means or when combined with a separate
Cable Seal - a seal that is installed at a cable termination
to prevent the release of an explosion from an
explosion-proof enclosure and that minimizes the passage of gases
or vapours at atmospheric pressure.
Conduit Seal - a seal that is installed in a conduit to prevent
the passage of an explosion from one portion of
the conduit system to another and that minimizes the passages of
gases or vapours at atmospheric pressure.
Degree of Protection - the measures applied to the enclosures
of electrical apparatus to ensure
(a) the protection of persons against contact with live or moving
parts inside the enclosure and protection of
apparatus against the ingress of solid foreign bodies; and
(b) the protection of apparatus against ingress of liquids.
Explosive Gas Atmosphere - a mixture with air,
under atmospheric conditions, of flammable substances in
the form of gas, vapour, or mist in which, after ignition, combustion
spreads throughout the unconsumed mixture.
Explosive Limits - the lower and upper percentage
by volume of concentration of gas in a gas-air mixture that
will form an ignitable mixture.
LEL - lower explosive limit.
UEL - upper explosive limit.
Methods of Protection - defined methods to
reduce the risk of ignition of explosive gas atmospheres.
Non-incendive Circuit - a circuit in which any spark
or thermal effect that may occur under normal operating
conditions or due to opening, shorting, or grounding of field
wiring is incapable of causing an ignition of the
prescribed flammable gas or vapour.
Normal Operation - the situation when the plant or equipment
is operating within its design parameters.
Primary Seal - a seal that isolates process fluids from an
electrical system and that has one side of the seal in
contact with the process fluid.
Secondary Seal - a seal that is designed to prevent the passage
of process fluids at the pressure it will be
subjected to upon failure of the primary seal.
Protective Gas - the gas used to maintain pressurization
or to dilute a flammable gas or vapour.
Header - A raceway for electrical conductors,
associated with an underfloor raceway or cellular floor system,
which provides access to predetermined raceways or cells.
Heating Systems - fixed electric space-heating
systems for heating rooms and similar areas; or fixed surface
heating systems for pipe heating, melting of snow or ice on roofs
or concrete or asphalt
surfaces, soil heating, and similar applications other than space
Special terminology and components:
Central unit - any heating unit (or group of units assembled
to form a complete unit) permanently installed
in such a way that it can convey heat to rooms or areas using air,
liquid, or vapour flowing through pipes or ducts;
and including duct heaters.
Fixture - any heating unit (or group of units assembled
so as to form a complete unit) permanently installed
in such a manner that it can be removed or replaced without removing
or damaging any part of the building structure.
Heating Device - any form of electrical heating
device, including cable, fixture, panel, and strip system.
Heating Device Set - a heating device assembled
with the associated parts necessary to connect it to a source
of electrical supply.
Heating Panel - a rigid or non-rigid laminated
plane section in which the heating element consisting of a
continuously parallel resistive material, a series resistive
material, or a parallel-series resistive material is embedded
between or in sheets of electrical insulating material.
Heating Panel Set - a heating panel together
with cold leads or a non-heating portion.
Parallel Heating Cable - a cable incorporating
heating elements connected in parallel either continuously or
intermittently such that the watt density along the length of
cable is not altered by changes in the cable length.
Parallel Heating Cable Set - the combination
of a parallel heating cable and associated parts necessary to
connect it to a source of electrical supply.
Sauna Heater - a device that is designed for
heating air and that is installed permanently in a special room
produce a hot atmosphere with generally a relatively low humidity,
although brief excursions to relatively high
humidity may take place.
Series Heating Cable - a cable using a series
Series Heating Cable Set - the combination
of a series heating cable and a means of connecting it to a source
of electrical supply where the combination is assembled by the
Heat Run Test - A test used to determine the
temperature rise of a device under rated load.
Heavy Duty - A lightning impulse classifying
current category for distribution class arresters defined by ANSI/IEEE
C62.11. A heavy duty rated arrester has a 10,000 amperage impulse
value crest (refer to normal duty).
Hertz (Hz) - Expression of ac frequency in cycles
per second, e.g., 60 Hz.
High-voltage - see definition for Voltage.
High Voltage and Low Voltage Windings - Terms
used to distinguish the winding having the greater voltage rating
from that having the lesser in two-winding transformers. The terminations
on the high voltage windings are identified by H1, H2,
etc., and on the low voltage by X1, X2, etc.
Hoistway - Any shaftway, hatchway, well hole,
or other vertical opening or space in which an elevator, escalator,
or dumbwaiter operates or is intended to operate.
Hot Tubs - see definition for Pools, Tubs, and Spas
HV - High voltage, see definition for Voltage.