Electrical Glossary

Double insulated symbol, indicates an appliance that does not need to be earthed due to extra precautions against shock. Such appliances are not necessary double insulated, despite the technically inaccurate name that would appear to imply they are.

2-way switching

A method of wiring switches so that a lamp can be turned on or off from more than one switch.

Accessory

Sockets, switches etc. All the visible bits of an electrical installation.

Appliance

An item of current-using equipment other than a lurninaire or an independent motor.

Arc

electrical conduction across insulation breakdown, often through air.

Ashathene

An obsolete plastic cable, a precursor of pvc. It lasts well, and is usually in good condition.

Ballast

Current control device used to run a fluorescent tube or other discharge lamp.

Basic insulation

Insulation applied to live parts to provide basic protection against electric shock and which does not necessarily include insulation used exclusively for functional purposes.

BC

Bayonet Cap, most popular type of lightbulb connection.

Bipin

2 pin connection used on fluorescent tubes & halogen lamps.

Bonding conductor

A protective conductor providing equipotential bonding.

Bunched

Cables are said to be bunched when two or more are contained within a single conduit, duct, ducting, or trunking or, if not enclosed, are not separated from each other by a specified distance.

Cable

CablesElectrical wire not intended for regular flexing. Has solid single core copper conductors. see also flex.

Cable clips

Clips that hold cable in place. Usually a plastic clip fixed in place with a small masonry nail, but other types also exist.

Cable ducting

An enclosure of metal or insulating material, other than conduit or cable trunking, intended for the protection of cables which are drawn in after erection of the ducting.

Cable ties

Self locking plastic strap to secure cables

Cable trunking

A closed enclosure normally of rectangular cross-section, of which one side is removable or hinged, used for the protection of cables and for the accommodation of other electrical equipment.

Cartridge fuse link

A device comprising a fuse element or several fuse elements connected in parallel enclosed in a cartridge usually filled with arc-extinguishing medium and connected to terminations (see fuse link).

CFL

Compact Fluorescent Lamp. Energy saving lamp used in place of filament lamps.

Chocolate block, choc block

screw connector strip for mains cables.

Circuit

An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s).

Circuit-breaker

A device capable of making, carrying and breaking normal load currents and also making and automatically breaking, under pre-determined conditions, abnormal cuiTents such as short-circuit currents. It is usually required to operate infrequently although some types are suitable for frequent operation.

Circuit protective conductor (CPC)

A protective conductor connecting exposed-conductive-parts of equipment to the main earthing terminal. AKA earth conductor, earth wire.

Circline

circular fluorescent tube

Class I equipment

Equipment in which protection against electric shock does not rely on basic insulation only, but which includes means for the connection of exposed-conductive-parts to a protective conductor in the fixed wiring of the installation.

Class II equipment

Equipment in which protection against electric shock does not rely on basic insulation only, but in which additional safety precautions such as supplementary insulation are provided, there being no provision for the connection of exposed metalwork of the equipment to a protective conductor, and no reliance upon precautions to be taken in the fixed wiring of the installation (see BS 2754).

Class III equipment

Equipment in which protection against electric shock relies on supply at SELV and in which voltages higher than those of SELV are not generated (see BS 2754).

Conduit

A part of a closed wiring system for cables in electrical installations, allowing them to be drawn in andlor replaced, but not inserted laterally.

Consumer unit (CU)

(may also be known as a consumer control unit or electricity control unit). A particular type of distribution board comprising a co-ordinated assembly for the control and distribution of electrical energy, principally in domestic premises, incorporating manual means of double-pole isolation on the incoming circuit(s) and an assembly of one or more fuses, circuit-breakers, residual current operated devices or signalling and other devices purposely manufactured for such use.

Contactor

Relay (electrical)

Current-carrying capacity of a conductor

The maximum current which can be carried by a conductor under specified conditions without its steady state temperature exceeding a specified value.

Current-using equipment

Equipment which converts electrical energy into another form of energy, such as light, heat or motive power.

Crossover Switch

Type of switch used only in 3 or more way switching.

Design current (of a circuit)

The magnitude of the current (rms value for a. c. ) to be carried by the circuit in normal service.

Dimmer

device for reducing the efficiency of filament bulbs.

Direct contact

Contact of persons or livestock with live parts.

Distribution board

An assembly containing switching or protective devices (e. g. fuses, circuit-breakers, residual current operated devices) associated with one or more outgoing circuits fed from one or more incoming circuits, together with terminals for the neutral and protective circuit conductors. It may also include signalling and other control devices. Means of isolation may be included in the board or may be provided separately.

Discharge Lighting

Lighting based on the principle of an arc. This includes fluorescent lights, sodium & mercury lights, and metal halide.

Discrimination

Ensuring that when a protective device clears a fault, as few circuits as possible (ideally only the affected circuit) are disconnected. In the case of cascaded protective devices such as MCBs or Fuses, there must be sufficient difference in their trip rating such that only one one nearest the fault trips. (with cascaded RCDs discrimination is usually achieved by have devices with progressively faster response times as you move further from the circuits origin).

Double insulation

Insulation comprising both basic insulation and supplementary insulation.

Earth

Electrical connection to earth / ground. The conductive mass of the Earth, whose electric potential at any point is conventionally taken as zero.

Earth electrode

A conductor or group of conductors in intimate contact with, and providing an electrical connection to, Earth.

Earth electrode resistance

The resistance of an earth electrode to Earth.

Earth fault current

A fault current which flows to Earth

Earth fault loop impedance

The impedance of the earth fault current loop starting and ending at the point of earth fault. This impedance is denoted by the symbol Zs.

Earth leakage

the flow of mains current to earth, sometimes via a human. Earth current is often fault current, though not always.

Earth wire

electrical wire connected to earth. See CPC.

Earthed equipotential zone

A zone within which exposed-conductive-parts and extraneous-conductive-parts are maintained at substantially the sam potential by bonding, such that, under fault conditions, the differences in potential between simultaneously accessible exposed- and extraneous-conductive-parts will not cause electric shock.

Earthing

Connection of the exposed-conductive-parts of an installation to the main earthing terminal of that installation.

Earthing conductor

A protective conductor connecting the main earthing terminal of an installation to an earth electrode or to other mews of earthing.

ELCB

Device to cut electrical power in the event of certain earth leakage faults. There are 2 different types of ELCB, current operated (aka RCD) and voltage operated. Now superceded by RCDs, the designation 'ELCB' indicates an old device.

Electric shock

A dangerous physiological effect resulting from the passing of an electric current through a human body or livestock.

Electrocution

Death by electric shock.

Enclosure

A part providing protection of equipment against certain external influences and in any direction protection against direct contact.

Equipotential bonding

Electrical connection maintaining various exposed-conductive-parts and extraneousconductive-parts at substantially the same potential.

ES

Edison Screw. The most common size of screw-in lightbulb base. See also SES, MES

Exposed-conductive-part

A conductive part of equipment which can be touched and which is not a live part but which may become live under fault conditions.

Extraneous-conductive-part

A conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation.

Fault

A circuit condition in which current flows through an abnormal or unintended path. This may result from an insulation failure or a bridging of insulation. Conventionally the impedance between live conductors or between live conductors and exposed- or extraneous-conductive-parts at the fault position is considered negligible.

Fault current

A current resulting from a fault.

Filament lamp

Traditional light bulb containing a white hot filament. See also GLS.

Final circuit

A circuit connected directly to current-using equipment, or to a socket-outlet or socket-outlets or other outlet points for the connection of such equipment.

Fixed equipment

Equipment designed to be fastened to a support or otherwise secured in a specific location.

Flexible cable (Flex)

A cable whose structure and materials make it suitable to be flexed while in service. The flexibility results from using stranded conductors.

Flexible cord

A flexible cable in which the cross-sectional area of each conductor does not exceed 4 mm2.

Fluorescent lamp

A highly energy efficient type of lighting.

Functional earthing

Connection to Earth necessary for proper functioning of electrical equipment.

Functional switching

An operation intended to switch 'on' or 'off' or vary the supply of electrical energy to all or part of an installation for normal operating purposes.

Fuse

A device which by the melting of one or more of its specially designed and proportioned components, opens the circuit in which it is inserted by breaking the current when this exceeds a given value for a sufficient time. The fuse comprises all the parts that form the complete device.

Fusebox

Box with switch & fuses. see also CU. See House Wiring for Beginners

Fuse carrier

The movable part of a fuse designed to carry a fuse link.

Fuse element

A part of a fuse designed to melt when the fuse operates.

Fuse link

A part of a fuse, including the fuse elerment(s), which requires replacement by a new or renewable fuse link after the fuse has operated and before the fuse is put back into service.

Gang

Specifies the number of duplicated components that are found on an accessory. Hence a fual gang socket or switch has two sockets or switches, a single gang, only one.

Grommet

rubber ring-shaped item that protects cables etc from the sharp edges of a hole. Also see blind grommet

Halogen lamp

a high temperature filament lamp. Popularly used as downlighters.

Harmonized Standard

A standard which has been drawn up by common agreement between national standards bodies notified to the European Commission by all member states and published under national procedures.

Humidistat

Device that switches electrical power according to humidity level. Usually switches power on when RH goes above its threshold value.

Intumescent Hood

Indirect contact

Contact of persons or livestock with exposed-conductive-parts which have become live under fault conditions.

Insulation

Suitable non-conductive material enclosing, surrounding or supporting a conductor.

Isolation

A function intended to cut off for reasons of safety the supply from all, or a discrete section, of the installation by separating the installation or section from every source of electrical energy.

Isolator

A mechanical switching device which, in the open position, complies with the requirements specified for isolation. An isolator is otherwise known as a disconnector.

Junction box

Box containing connection points for cables. Fire resistant.

LED

Miniature solid state light emitter. Very low powered devices available in white and assorted monochromatic colours.

Leakage current

Electric current in an unwanted conductive path under normal operating conditions.

Line

Live wire

Live part

A conductor or conductive part intended to be energised in normal use, including a neutral conductor but, by convention, not a PEN conductor.

Low noise earth

An earth connection in which the level of conducted or induced interference from external sources does not produce an unacceptable incidence of malfunction in the data processing or similar equipment to which it is connected. The susceptibility in terms of ainplitudelfrequency characteristics varies depending on the type of equipment.

Luminaire

Equipment which distributes, filters or transforms the light from one or more lamps, and which includes any parts necessary for supporting, fixing and protecting the lamps, but not the lamps themselves, and, where necessary, circuit auxiliaries together with the means for connecting them to the supply. For the purposes of the Regulations a lampholder, however supported, is deemed to be a luminaire.

M3.5

the size & thread of screws used with standard UK electrical accessory faceplates.

Main earthing terminal

The terminal or bar provided for the connection of protective conductors, including equipotential bonding conductors, and conductors for functional earthing, if any, to the means of earthing.

MCB

Miniature Circuit Breaker, a pushbutton overcurrent cutout that replaces a fuse

Mercury Lamp

A high efficiency white discharge lamp with poor light quality. Sometimes used as white streetlights. Not as popular as they were 20-30 years ago.

MES

Miniature Edison Screw: screw-in bulb base widely used on torch bulbs.

Metal Halide Lamp

High efficacy white discharge light available in various versions of white.

MICC

Mineral insulated copper cable. A very high temperature rated rigid cable. Widely used for fire critical circuits. Known as pyro. Hygroscopic.

Multimeter

electrical meter that measures voltage, current (amps) and resistance. A worthwhile purchase for almost any DIYer.

Neon screwdriver

Simple voltage indicator. It is unsafe to rely on these when dealing with mains, as they give both false positive and false negative results.

Neutral conductor

A conductor connected to the neutral point of a system and contributing to the transmission of electrical energy. The term also means the equivalent conductor of an IT or d. c. system unless otherwise specified in the Regulations and also identifies either the mid-wire of a three-wire d. c. circuit or the earthed conductor of a two-wire earthed d,c. circuit.

Origin of an installation

The position at which electrical energy is delivered to an electrical installation.

Overcurrent

A current exceeding the rated value . For conductors the rated value is the current-carrying capacity.

Overcurrent detection

A method of establishing that the value of current in a circuit exceeds a predetermined value for a specified length of time.

Overload current

An overcurrent occurring in a circuit which is electrically sound.

PAR38 & other numbers

Spotlight bulbs.

* PAR number gives bulb diameter in 1/8ths of an inch

PAT

Portable Appliance Test, electrical goods safety test.

Pattress

Backbox for electrical accessories (light switches, sockets, etc)

PEN conductor

A conductor combining the functions of both protective conductor and neutral conductor.

Phase conductor

A conductor of an a. c. system for the transmission of electrical energy other than a neutral conductor, a protective conductor or a PEN conductor. The term also means the equivalent conductor of a d. c. system unless otherwise specified in the Regulations.

Plug

A device, provided with contact pins, which is intended to be attached to a flexible cable, and which can be engaged with a socket-outlet or with a connector.

Portable equipment

Electrical equipment which is moved while in operation or which can easily be moved from one place to another while connected to the supply.

Protective conductor

A conductor used for some measures of protection against electric shock and intended for connecting together any of the following parts: (i) exposed-conductive-parts (ii) extraneous-conductive-parts (iii) the main earthing terminal (iv) earth electrode(s) (v) the earthed point of the source, or an artificial neutral.

Prospective fault current

The value of overcurrent at a given point in a circuit resulting from a fault of negligible impedance between live conductors having a difference of potential under normal operating conditions, or between a live conductor and an exposed-conductive-part.

Protective conductor current

Electric current which flows in a protective conductor under normal operating conditions.

Protective multiple earthing (PME)

An earthing arrangement, found in TN-C-S systems, in which the supply neutral conductor is used to connect the earthing conductor of an installation with Earth, in accordance with the Electricity Safety, Quality and Continuity Regulations 2002 (see also figure 5).

PV

Solar PhotoVoltaic, an electricity producing solar panel.

R50

50mm diameter spotlight bulb.

R63

63mm diameter spotlight bulb.

R80

80mm diameter spotlight bulb.

RCBO

an MCB & RCD in one device. See Electricity Basics & Rewiring Tips

RCD

device that cuts the power if it detects earth leakage. See also Rewiring Tips. Compare ELCB.

Relay

Electrically controlled switch. The first electrical computers were made from thousands of relays.

Residual current

Algebraic sum of the currents in the live conductors of a circuit at a point in the electrical installation.

Residual current device

A mechanical switching device or association of devices intended to cause the opening of the contacts when the residual current attains a given value under specified conditions.

Residual operating current

Residual current which causes the residual current device to operate under specified conditions.

Ring final circuit (Ring circuit)

A final circuit arranged in the form of a ring and connected to a single point of supply.

SBC

Small Bayonet Cap. Miniature version of the more popular bayonet cap used on mains light bulbs.

SES

Small Edison Screw. The 2nd most common size of screw-in lightbulb base, smaller than ES.

SELV (separated extra-low voltage)

An extra-low voltage system which is electrically separated from Earth and from other systems in such a way that a single fault cannot give rise to the risk of electric shock.

Shock current

A current passing through the body of a person or livestock such as to cause electric shock and having characteristics likely to cause dangerous effects.

Short-circuit current

An overcurrent resulting from a fault of negligible impedance between live conductors having a difference in potential under normal operating conditions.

Simultaneously accessible parts

Conductors or conductive parts which can be touched simultaneously by a person or, in locations specifically intended for them, by livestock.

Simultaneously accessible parts

may be: live parts, exposed-conductive-parts, extraneous-conductive-parts, protective conductors or earth electrodes.

Singles

Cable with a single conductor. Used inside conduit & trunking

Socket

electrical outlet into which a plug can be inserted.

Socket-outlet

See socket. A device, provided with female contacts, which is intended to be installed with the fixed wiring, and intended to receive a plug.

Spur

A branch from a ring final circuit.

Sodium Lamp

2 different types of very high efficacy yellow and pink lighting. Much used for road lighting. Low pressure sodium lighting has the best energy efficiency of all lighting types.

Solder

Metal alloy used to join pipes and sometimes wiring. Lead & tin solder has long been used, but is no longer permitted for potable water piping.

Striplight

Linear lamp, either fluorescent or filament

Supplementary insulation

Independent insulation applied in addition to basic insulation in order to provide protection against electric shock in the event of a failure of basic insulation.

Switch

A mechanical device capable of making, carrying and breaking current under normal circuit conditions, which may include specified operating overload conditions, and also of carrying for a specified time currents under specified abnormal circuit conditions such as those of short-circuit. It may also be capable of making, but not breaking, short-circuit currents.

Switch, linked

A switch the contacts of which are so arranged as to make or break all poles simultaneously or in a definite sequence.

Switchbank

Bank of 2 or more switches. Permits much greater control over lighting etc than just a single switch. Compare 'dimmer.'

Switchboard

An assembly of switcligear with or without instruments, but the term does not apply to groups of local switches in final circuits.

Switchfuse

Switch & fuse. Historic forerunner of the fusebox

Switchgear

An assembly of main and auxiliary switching apparatus for operation, regulation, protection or other control of an electrical installation.

T4, T5, T8, T12

Diameters of fluorescent tubes, in 1/8ths of an inch. Thus T12 is 1.5" diameter.

T&E

Twin & Earth, 3 core PVC cable used for most house wiring.

Trip

Any button or switch operated electrical cut-out, such as MCB, RCD, RCBO. A colloquial term.

TT

Earthing system using a local earth, usually a rod but may sometimes be a pipe or grid.

Ufer

A method of creating a very low resistance local earth connection, and eliminating potential differences between concrete floors and CPC during fault conditions, all at no significant cost.

VA

Volts multiplied by amps gives VA. This equals power for some loads, but is not equal to power for non-resistive loads.

Whole House RCD

A deprecated way of installing an RCD such that a single low trip threshold device (typically 30mA) protects all the circuits in a property. While counter to the advice given in the present wiring regulations. installations of this type are still commonly found.

VIR

Indian rubber electrical wiring. Common half a century ago.

See Also

Glossary

Category:Electrical

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