Glossary
Glossary of terms and phrases used on this
site
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AC - Alternating current
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Bending Radius - The amount that a cable
can be bent, specified as the internal radius of a bend.
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Bonding conductor - Conductors that
are installed to electrically link items of metalwork within a building thereby
ensuring that an earth fault has a minimum return resistance. Further divided
into Equipotential Bonding and Supplementary Bonding.
Adequate bonding ensures fast disconnection times and that the touch voltage
between metalwork does not exceed 50volts.
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Card reader - A device which can read
a magnetic code on a small card (like a credit card). If the code is correct
then a signal is initiated. Such devices are commonly used for door access
systems where only a certain code allows access tot he door.
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Clean earth - this is a specialised form
of CPC that is installed to serve sensitive electronic equipment.
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Clean supply - An electrical supply that
is independently served, separated from other equipment (particularly motors),
and serves dedicated equipment. Commonly used for supplies to electronic
or data equipment.
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Circuit Protective Conductor - A conductor
that is installed in order to provide a guaranteed earth return path for
an individual circuit. Thereby ensuring fast disconnection times
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Coaxial - A type of cable which
has a single central conductor surrounded by special packed insulation. Commonly
used for Video and data
signalling.
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Comfort - A subjective term. Used to
describe the apparent well being and comfort of an individual in given
environmental conditions. The main factors affecting comfort are lighting,
temperature, humidity, noise and air movement.
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Compartmentation - Where the internal structure
of a item of equipment is divided up into
compartments.
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Conductor - A material that is able
to pass an electric current. The central core of a cable is a conductor.
Common conductors in use are copper and aluminium.
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Current Transformer - A special form of
transformer used in protection and instrumentation. A high current is measured
and is stepped down to typically 1A for use with electronic or electromagnetic
relays or related devices.
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DC - Direct
current
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Discharge lamp - Varying forms exist
- the high & low pressure sodium (SON & SOX), high pressure mercury
(MBF) as well as numerous variants using complex gases.
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Disconnection time - The time taken for
a protection device to operate and disconnect the circuit following
a fault
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Discrimination - The process by
which it is ensured that a protective device will trip or blow before any
devices which are nearer the supply or
"upstream"
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Door Contact - A switch that is built
into the frame of latch of a door. If opened then an alarm is activated.
A common form of door contact relies on a magnet opening and closing a reed
switch (small magnetically operated switch) Commonly used in security alarm
systems
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Escape route - A defined path or route
through a building which should be used during an emergency escape situation.
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Fault Current - The current that will flow
in the event of a fault. It is proportional to the fault level.
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Fault level - The amount of available energy
at a point in an installation. Usually expressed in KVA.
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Final Circuit - An electric circuit
that feeds individual equipment or groups of equipment used in the
building. Such circuits normally have ratings up to
45A
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Fire compartmentation - Areas of a building
that are able to contain a fire for a given time without spreading to adjacent
areas. Dictates how a fire alarm system is zoned.
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Fire Fighting Lift - A lift that is designated
for use by the Fire Brigade during a fire condition
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Fixed temperature detector - Part of a
fire alarm system designed to detect fire. Uses a thermocouple or thermistor
to sense the ambient temperature. If a given temperature is exceeded, an
electronic circuit causes an alarm condition.
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Fluorescent lamp - A form of low pressure
mercury discharge lamp, the common fluorescent lamp is used throughout industrial
and commercial installations for both general and specialised lighting
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Flywheel - A mechanical device that
comprises a heavy rotating wheel. It is normally powered by a motor, and
stores kinetic energy. If the motor supply fails, the flywheel keeps spinning.
Commonly linked to a generator for UPS purposes.
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Glare - Term describing the effect of unwanted
light falling on a surface or affecting normal vision. Commonly identified
as a problem where VDUs are used and reflections of luminaires can be seen
in VDU screens.
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GLS lamp - General Lighting Service - A form
of tungsten lamp
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Harmonic - A form of electrical
interference caused commonly by electronic equipment. Various non standard
waveforms are mixed with the standard supply waveform. This causes strange
voltages and currents to appear at certain frequencies.
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Inductive load. - A load that has inductive
properties (inductive reactance). Common forms are motors, transformers,
wound control gear. Inductive loads can caused excessive voltages to appear
when switched. This can damage equipment. The power factor of an installation
is also affected by inductive loads.
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Illumination levels - The amount of
light falling on a surface. Measured in Lumens/m² or "Lux".The required
illumination level is dependent upon the use and type of room.
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Ingress protection - An international rating
system which classifies the ability of an item of equipment to withstand
ingress from either solid particles or liquids. Termed the "IP rating"
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Insulation - A material that will
not pass an electric current except at high voltages (breakdown voltage).
Used to surround a conductor and within equipment and switchgear to avoid
possibility of personal contact with live parts. Common insulators are PVC,
XLPE & Rubber
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Ionisation detector - Part of a fire
alarm system designed to detect fire. Uses mild radioactive isotope which
emits alpha particles within a chamber which, if they hit smoke particles
are deflected onto a sensor which causes an alarm.
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Light Source - The type of lamp that
is used in a luminaire. ie: GLS, SON, SOX MBF
etc.
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Luminaire - Term used in professional
circles to describe a lighting fitting. ie: an item of equipment designed
to emit light.
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Low Smoke & Fume (LSF) - Type of insulation
that when it burns emits only small amounts or toxic fumes and smoke. Desirable
in many buildings.
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Main Earthing Terminal (MET) - The main
connection point for all main binding conductors within an installation.
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Microwave detectors - Electronic monitoring
device which sends high frequency radio pulses into a room and "listens"
to the echos caused. If the pattern of echos changes (such as a person walking
across detection area) then an alarm is
activated
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Monitoring station - A remote site,
often commercially run, which constantly receives a signal from an alarm
system. An alarm will initiate an automatic alarm at the monitoring station,
appropriate action is then taken (ie: calling police or fire brigade)
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Multiplex - Where more than one electrical
signal is passed along a single cable.
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Optical detector - Part of a fire alarm
system designed to detect fire. Uses a tiny beam of light which shines across
a small chamber to a receiver. If the beam is broken or disrupted, then an
alarm is activated.
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Passive Infra Red (PIR) detectors - Electronic
monitoring device that registers a "heat image" of an area. If the image
changes (such as a person walking across detection area) then an electronic
signal is registered. Commonly used in security alarm systems also for local
presence switching applications.
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Photocell - A form of switch that is operated
by light. Mostly used for automatic switching of external lighting to coincide
with setting of the sun.
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Portable Equipment - Electrical Equipment
that is able to be plugged in and out of socket outlets. Hence is transportable
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Protection device - A device that
is installed in order to protect life and equipment. Common forms or protection
are short circuit protection, overload protection and earth leakage protection.
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Poly Vinyl Chloride (PVC) - Type of plastic
based insulation material. Derived from oil.
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Power Factor - A measure of the angular
displacement between the voltage and the current in a supply system. ranges
in vale from 0-1 (Cosine of the angle between V & I). Greatly affects
the performance of the installation, unnecessary current may be drawn if
a poor power factor is present. Most supply authorities charge users high
penalty charges if the installation power factor is below 0.9. A low power
factor is caused by the presence of inductive loads in the installation.
Can be corrected using power factor
correction.
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Prime Mover - A machine or energy
source that provides initial kinetic energy for rotating machinery such as
generators.
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Private Generation - The use of generator
sets in a private capacity ie:- electricity not derived from public supply
systems.
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Rate of rise detector. - Part of a fire alarm
system designed to detect fire. Uses a thermocouple or thermistor to sense
the ambient temperature. If the temperature rises at more than a preset rate,
then an electronic circuit causes an alarm condition.
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Regulations, The IEE
Wiring - An all encompassing set of documents relating to the
standard by which electrical installations should be installed.
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Residual Current Device (RCD) - A safety
device (a modified circuit breaker), usually installed within a distribution
board which monitors the circuit that is is serving. In the event of a earth
fault or "earth leakage" contacts will open and the supply will be
isolated. Used to enhance protection where the adequacy of the earth return
path may be suspect.
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Renewable energy - Energy that is derived
from sources such as wind, solar, hydroelectric or geothermal resources.
Environmentally friendly.
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Repeater panel - A indication panel
which mimics the displays and other features of a main control panel. The
panel can be functional (where controls are also included) or non-functional
(where indicators only are included). Commonly used on fire alarm systems.
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Ring Main - A form of final circuit wiring
which is wired in a circular or "ring fashion" Current passes around the
ring both ways and hence a smaller cable can be used.
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SCR - Silicon Controlled Rectifier. A
semiconductor device used to convert AC to DC. Commonly used in motor drive
applications and UPS
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Segregation - Where equipment is
divided up into parts or compartments, and different services are installed
in different compartments. Commonly applied to trunking systems and switchgear.
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Star Point - Point of connection on the
centre of a transformer that is wound in a star format (usually the secondary)
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Sub Circuit - A term used to describe
a circuit which branches from sub-main circuits but does not directly feed
a final circuit.
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Sub Main - Term describing the main cabling
running from mains intake to serve distribution equipment throughout the
building
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Timeclock - A colloquial term. A form
of switch that is linked to a clock mechanism. Various forms enable various
switching patterns to be applied at different times of the day.
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Touch Voltage - The voltage present
between an item of exposed metalwork and the general mass of earth.
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Tungsten Lamp - A lamp relying on a
tungsten wire that is heated until it glows white hot. Heat is caused by
its own resistance.
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Tungsten Halogen Lamp - A form of tungsten
lamp in which the filament is surrounded by a halogen gas mixture. In crease
light output is possible to the the filament operating at a higher
temperature.
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Ultrasonic detectors - Electronic
monitoring device which sends high frequency pulses of sound into a room
and "listens" to the echos caused. If the pattern of echos changes (such
as a person walking across detection area) then an alarm is activated.
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Visual Display Unit (VDU) - A computer screen,
monitor or other form of display. Use of VDUs can have implications for
electrical services design
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VESDA - Very Early Smoke Detection and
Alarm. A sensitive item of equipment connected to a fire alarm system. Uses
a small fan and a network of small ducts to bring air from the space into
a sampling chamber. Very sensitive devices are then used to sample for the
first signs of a fire (even a few particles will initiate an alarm). Commonly
used for sensitive electronic equipment.
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XLPE - Cross Linked Polyethylene A modern
thermosetting plastic used as an electrical insulator.


