Glossary

Glossary of terms and phrases used on this site

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• AC - Alternating current
• Bending Radius - The amount that a cable can be bent, specified as the internal radius of a bend. 
• 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.
• 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.
• Clean earth - this is a specialised form of CPC that is installed to serve sensitive electronic equipment.
• 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.

• 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
• Coaxial - A type of cable which has a single central conductor surrounded by special packed insulation. Commonly used for Video and data signalling.
• 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.
• Compartmentation - Where the internal structure of a item of equipment is divided up into compartments.
• 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.
• 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 
• Discharge lamp - Varying forms exist - the high & low pressure sodium (SON & SOX), high pressure mercury (MBF) as well as numerous variants using complex gases.
• Disconnection time - The time taken for a protection device to operate and disconnect the circuit  following a fault
• 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"
• 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
• Escape route - A defined path or route through a building which should be used during an emergency escape situation.
• Fault Current - The current that will flow in the event of a fault. It is proportional to the fault level.
• Fault level - The amount of available energy at a point in an installation. Usually expressed in KVA.
• 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
• 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. 
• Fire Fighting Lift - A lift that is designated for use by the Fire Brigade during a fire condition
• 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.
• 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
• 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.
• GLS lamp - General Lighting Service - A form of tungsten lamp
• 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.
• 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.
• 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. 
• 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"
• 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
• 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.   
• Light Source - The type of lamp that is used in a luminaire. ie: GLS, SON, SOX MBF etc.
• Luminaire - Term used in professional circles to describe a lighting fitting. ie: an item of equipment designed to emit light.
• 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.
• 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 
• 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)
• Multiplex - Where more than one electrical signal is passed along a single cable.
• 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.
• 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. 
• 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.
• Portable Equipment - Electrical Equipment that is able to be plugged in and out of socket outlets. Hence is transportable
• 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.
• Poly Vinyl Chloride (PVC) - Type of plastic based insulation material. Derived from oil.
• 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.
• Prime Mover - A machine or energy source that provides initial kinetic energy for rotating machinery such as generators.
• 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.
• Regulations, The IEE Wiring - An all encompassing set of documents relating to the standard by which electrical installations should be installed.
• 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.  
• Renewable energy - Energy that is derived from sources such as wind, solar, hydroelectric or geothermal resources. Environmentally friendly.
• 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.
• 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.
• SCR - Silicon Controlled Rectifier. A semiconductor device used to convert AC to DC. Commonly used in motor drive applications and UPS 
• 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.
• Star Point - Point of connection on the centre of a transformer that is wound in a star format (usually the secondary)
• Sub Circuit - A term used to describe a circuit which branches from sub-main circuits but does not directly feed a final circuit. 
• Sub Main - Term describing the main cabling running from mains intake to serve distribution equipment throughout the building
• 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.
• Touch Voltage - The voltage present between an item of exposed metalwork and the general mass of earth.
• Tungsten Lamp - A lamp relying on a tungsten wire that is heated until it glows white hot. Heat is caused by its own resistance.
• 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. 
• Visual Display Unit (VDU) - A computer screen, monitor or other form of display. Use of VDUs can have implications for electrical services design
• 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. 
• XLPE - Cross Linked Polyethylene A modern thermosetting plastic used as an electrical insulator.