Andrew Neish


Tel: 01428 723 483

Mob: 07779 360 393

Understanding Electricians

Some electrician's terms, acronyms, abbreviations and phrases explained.

Word or PhraseAbbreviationMeaning
Amp or AmpereAThe unit of electrical current flow.
Accessory An electrical device other than an item of current-using equipment. eg switches, sockets, FCUs, etc.
Alternating currentACElectricity which regularly reverses its direction of flow (in the case of UK mains, it reverses direction every 1/100th of a second, ie 50 complete "cycles" per second, or 50Hz).
Bayonet capBCType of lamp base requiring a push-and-turn action to insert into lampholder. (See also ES.)
BS 7671 The British Standard "Requirements for Electrical Installations". This standard is currently (as at January 2012) BS 7671:2008, incorporating Amendment No 1:2011; with the dual title of "IET Wiring Regulations, Seventeenth Edition". Formerly known as the IEE Wiring Regulations. Slang, the "Big Green Book". It is the main document detailing the requirements for electrical installations in the UK.
Cartridge fuse Fuse enclosed in a (usually) ceramic tube with a metal contact cap at each end. Available in various sizes and current ratings. As used in a 13A plug, for example.
Circuit The electrical distribution equipment supplied from a fuse or circuit breaker. Consisting of cable and accessories.
Circuit breakerCBA device for automatically breaking an electrical circuit under fault conditions, eg over-current or short circuit.
Circuit protective conductorCPCUsually the "earth wire" in a cable.
Compact fluorescent lampCFLA type of low energy lamp.
Cooker connection unitCCUThe isolating switch for a cooker, oven or hob, sometimes incorporating a socket outlet.
Conduit Metal or plastic tubing for electrical cables. Usually round in section. usually rigid, unless described as flexible conduit.
Consumer control unitCCUSee consumer unit.
Consumer distribution unitCDUSee consumer unit.
Consumer unitCUThe item of equipment containing a main switch or main RCD and one or more circuit breakers, RCDs or RCBOs. Usually the main point at which the incoming supply is connected to the final circuits. It protects the fixed wiring in the building and provides a point of isolation. A consumer unit is a type of distribution board.
Direct currentDCElectricity which flows in one direction, as from a battery.
Distribution boardDBItem of equipment for connecting circuits to a supply. May contain a main switch, RCDs, circuit breakers, RCBOs, fuses, etc.
Distribution circuit Electrical circuit supplying a secondary distribution board.
Distribution network operatorDNOThe company responsible for distributing electricity to your house. (Not the electricity supply company that sends you your electricity bills.) The DNO is paid by your electricity supply company for carrying the electricity. The local DNOs are Scottish and Southern Electricity (SSE) and UK Power Networks (UKPN).
Double poleDPUsually used in the description of a switch (both line and neutral switched).
Earth leakage circuit breakerELCBForerunner to the RCD. Available in two types: voltage operated (now obsolete) and current operated (now called RCD).
Edison screwESType of lamp base which screws into a lampholder. (See also BC.)
Electrical installation condition reportEICRA document used to report on the condition of an existing electrical installation. Replaced the PIR from January 2012.
Extra low voltage An electrical supply of up to 50V AC. For example, a 12V supply for lighting would be "extra low voltage".
Final circuit Electrical circuit directly supplying socket outlets, lighting, cooker, etc.
Flush When applied to wiring accessories, it means that the backbox for the accessory is sunk into the wall so that just the faceplace protrudes. (Opp. surface)
Fuse A device which protects a circuit by the melting of a short length of wire of specific size and material when an excessive current flows, thus disconnecting the supply.
Fuse box or fuse board See distribution board. Now largely being replaced by consumer units containing MCBs.
Fused connection unitFCUElectrical accessory containing a cartridge fuse, usually the same size as a single socket, sometimes with a switch, neon indicator or flex outlet. Used to connect and protect an item of equipment or a low current spur on a higher current circuit.
Fused spur unitFSUSee FCU.
General lighting serviceGLSThe traditional type of incandescent lamp (light bulb). Has either a BC or ES base. Now being replaced by CFLs and other low energy types.
HertzHzUnit of measure of frequency. One Hz = one cycle per second.
Ingress protectionIPA rating system to describe the degree of protection of an enclosure against solid objects (eg fingers, dust) and liquids (eg rain).
Insulation resistanceIRThe measure of how well an electrical circuit or equipment resists the "leakage" of electricity.
Lamp A light source. Electrician's word for a light bulb. (Bulbs grow in gardens!)
Light-emitting diodeLEDA semiconductor device which emits light when supplied with electricity. For many years these were available in a limited range of colours and had low output. Used for indicators and displays on equipment. Now developing rapidly into a viable light source for general illumination. More energy efficient than most traditional lamp types. Still fairly high initial cost.
LineLUsed to describe one of the terminals or cable cores in a typical mains supply. This conductor will normally be at a raised voltage compared to earth. Formerly "live" or "phase".
Live The term for all the conductors which carry the normal operating current. These are the line and neutral conductors.
Local authority building controlLABCThe local authority department which controls building standards, including electrical installation.
Low voltage An electrical supply of more than 50V AC and up to 1000V AC. The domestic UK mains supply is "low voltage".
Luminaire Electrician's word for a light fitting.
Megger One make of electrical test equipment. "To Megger" is sometimes used to mean "to perform an insulation resistance test on".
Miniature circuit breakerMCBA small circuit breaker, usually fitted in a consumer unit or distribution board.
Multi-function testerMFTAn electrical installation tester. Usually capable of measuring continuity, insulation resistance, loop impedance, RCD disconnection times, etc.
Multimeter Meter for electrical testing but not, in itself, sufficient for installation testing.
NeutralNUsed to describe one of the terminals or cable cores in a typical mains supply. This conductor will normally be at about the same voltage as "earth".
Passive infra redPIRUsed to describe a sensor which will detect movement of objects at a different temperature to the surroundings, eg. people or animals. Used to turn on lighting or as part of an intruder alarm system.
Pendant A light which hangs down from the ceiling.
Periodic inspection reportPIRA document used to report on the condition of an existing electrical installation. Now replaced by the EICR.
Radial circuit A circuit arranged so that the cable runs from the origin (CU or fusebox) to one or more accesories or loads. The cable does not return to the origin, unlike a ring circuit.
Residual current circuit breakerRCCBSee RCD.
Residual current deviceRCDA circuit protection device which detects the current difference between the live conductors of a circuit and disconnects the circuit from the supply if the differential current exceeds a set value. It provides a higher level of protection against injury or death from an electric shock than a fuse or circuit breaker, although these are still necessary on any circuit.
Residual current circuit breaker with overcurrent protectionRCBOA circuit protection device combining the functions of a circuit breaker and an RCD.
Ring final circuitRFCA final circuit arranged so that the cable runs from the origin (CU or fusebox) via several accessories and returns to the origin. Typically used for socket outlets. Incorrectly called a "ring main".
Scottish and Southern ElectricitySSEOne of the local DNOs, responsible for distributing electricity to your house. Covering what was the Southern Electricity Board area. This is the whole of central southern England, from around Chobham, Aldershot, Godalming, Liphook and Chichester westwards.
Small bayonet capSBCType of lamp base requiring a push-and-turn action to insert into lampholder. (See also BC and ES.)
Small Edison screwSESType of lamp base which screws into a lampholder. (See also ES and BC.)
Spur A cable supplying a socket or other accessory, which branches off a circuit, usually from a RFC. A spur may be "fused" (by means of a FCU) or "unfused". There are well defined rules for spurs on a RFC.
Steel wire armouredSWAA type of cable with a layer of steel wire strands around the centre conductors, providing mechanical protection. Suitable for outdoor and underground supplies; eg, to sheds and detached garages.
Surface When applied to wiring accessories, it means that the accessory backbox is fixed to the face of the wall and not sunk in (as opposed to "flush").
When applied to cabling, it means that the cable, or the conduit or trunking enclosing it, is visible on the surface of the wall.
Trunking Long metal or plastic enclosure with removable lid for enclosing cables. Usually rectangular in section.
UK Power NetworksUKPNOne of the local DNOs, responsible for distributing electricity to your house. Covering what was the South Eastern Electricity Board area. This is the whole of south east England, from around Woking, Guildford, Cranleigh and Pulborough eastwards.
VoltVUnit of electrical "pressure". The UK mains is now (2012) nominally 230V with a tolerance of +10% and -6%, which is 216.2V to 253V.
Wiring Regs See BS 7671.