Starting from the IET Wiring Regulations17th Edition, then adding extras and comments, the aim is to try to produce a glossary of terms, which the ordinary person should be able to understand. However as a result there may be some items where there is some debate as to the precise meaning, and therefore these definitions should only be considered as a guild, and where the precise meaning is required then one should look elsewhere..

Accessory. A device, other than current-using equipment, associated with such equipment or with the wiring of an installation.
Agricultural and horticultural premises. Rooms, locations or areas where:
- livestock are kept, or
- feed, fertilizers, vegetable and animal products are produced, stored, prepared or processed, or
- plants are grown, such as greenhouses.
Ambient temperature. The temperature of the air or other medium where the equipment is to be used.
Amusement device. Ride, stand, textile or membrane building, side stall, side show.. tent, booth or grandstand intended for the entertainment of the public.
Appliance. An item of current-using equipment other than a luminaire or an independent motor.
Arm's reach. A zone of accessibility to touch, extending from any point on a surface where persons usually stand or move about to the limits which a person can reach with a hand in any direction without assistance. (See Figure 417)
Arrangements for livestock keeping. Buildings and rooms (housing for animals), cages, runs or other containers used for continuous accommodation of livestock.
Back-up protection. Protection which is intended to operate when a system fault is not cleared, or abnormal condition not detected, in the required time because of failure or inability of other protection to operate or failure of the appropriate circuit-breaker(s) to trip.
Barrier. A part providing a defined degree of protection against contact with live parts from any usual direction of access
Basic insulation. Insulation applied to live parts to provide basic protection and which does not necessarily include insulation used exclusively for functional purposes.
Basic protection. Protection against electric shock under fault-free conditions.
NOTE: For low voltage installations, systems and equipment, basic protection generally corresponds to protection against direct contact, that is "contact of persons or livestock with live parts".
Basin of fountain. A basin not intended to be occupied by persons and which cannot be accessed (reached by persons) without the use of ladders or similar means. For basins of fountains which may be occupied by persons, the requirements for swimming pools apply.
Bonding conductor. A protective conductor providing equipotential bonding.
Booth. Non-stationary unit, intended to accommodate equipment generally for pleasure or demonstration purposes.
Building void, accessible. A space within the structure or the components of a building accessible only at certain points. Such voids include the space within partitions, suspended floors, ceilings and certain types of window frame, door frame and architrave.
Building void, non-accessible. A space within the structure or the components of a building which has no ready means of access.
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.
Busbar trunking system. A type-tested assembly, in the form of an enclosed conductor system comprising solid conductors separated by insulating material. The assembly may consist of units such as:
- busbar trunking units, with or without tap-off facilities
- tap-off units where applicable
- phase-transposition, expansion, building-movement, flexible, end-feeder and adaptor units.
NOTE: Other system components may include tap-off units.
Cable bracket. A horizontal cable support system, consisting of elements fixed at one end only, spaced at intervals along the length of the cable and on which the cable rests.
Cable channel. An enclosure situated above or in the -round, ventilated or closed, and having dimensions which do not permit the access of persons but allow access to the conduits and/or cables throughout their length during and after installation. A cable channel may or may not form part of the building construction.
Cable cleat. A component of a support system, which consists of elements spaced at intervals along the length of the cable or conduit and which mechanically retains the cable or conduit.
Cable coupler. A means of enabling the connection or disconnection, at will, of two flexible cables. It consists of a connector and a plug.
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 ladder. A cable support consisting of a series of transverse supporting elements rigidly fixed to main longitudinal supporting members.
Cable tray. A cable support consisting of a continuous base with raised edges and no covering. A cable tray may or may not be perforated.
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.
Cable tunnel. A corridor containing supporting structures for cables and joints and/or other elements of wiring systems and whose dimensions allow persons to pass freely throughout the entire length.
Caravan. A trailer leisure accommodation vehicle, used for touring, designed to meet the requirements for the construction and use of road vehicles (see also definitions of Motor caravan and Leisure accommodation vehicle).
Caravan park / camping park. Area of land that contains two or more caravan pitches and/or tents.
Caravan pitch. Plot of ground intended to be occupied by a leisure accommodation vehicle.
Caravan pitch electrical supply equipment. Equipment that provides means of connecting and disconnecting supply cables from leisure accommodation vehicles or tents with a mains electrical supply.
Cartridge fuse link. A device comprising a fuse element or two or more fuse elements connected in parallel enclosed in a cartridge usually filled with arc-extinguishing medium and connected to terminations (see fuse link).
Central power supply system. A system supplying the required emergency power to essential safety equipment.
charged: the item has acquired a charge either because it is live or because it has become charged by other means such as by static or induction charging, or has retained or regained a charge due to capacitance effects even though it may be disconnected from the rest of the system (hsg85)
Circuit. An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s). Note the use of a FCU does not seem to be reguarded as forming a circuit under the British Part P building regulations.
Circuit-breaker. A device capable of making, carrying and breaking normal load currents and also making and automatically breaking. under pre-determined conditions, abnormal currents such as short-circuit currents. It is usually required to operate infrequently although some types are suitable for frequent operation.
Circuit-breaker, linked. A circuit-breaker the contacts of which are so arranged as to make or break all poles simultaneously or in a definite sequence.
Circuit protective conductor (cpc). A protective conductor connecting exposed-conductive-parts of equipment to the main earthing terminal.
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 (see BS EN 61140).
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 EN 61140) .
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 EN 61140).
Cold tail. The interface between the fixed installation and a heating unit.
Competent person. A person who possesses sufficient technical knowledge, relevant practical skills and experience for the nature of the electrical work undertaken and is able at all times to prevent danger and, where appropriate, injury to him/herself and others.
Complementary floor heating. Direct heating system integrated into the floor construction, for example. in the border zones close to outer walls, which complements the heat dissipation of a thermal storage floor heating system.
Conducting location with restricted movement. A location comprised mainly of metallic or conductive surrounding parts, within which it is likely that a person will come into contact through a substantial portion of their body with the conductive surrounding parts and where the possibility of preventing this contact is limited.
Conduit. A part of a closed wiring system for cables in electrical installations, allowing them to be drawn in and/or replaced, but not inserted laterally.
Connector. The part of a cable coupler or of an appliance coupler which is provided with female contacts and is intended to be attached to the end of the flexible cable remote from the supply.
Consumer unit (CU) (may also be known as a consumer control unit or electricity control unit). A particular type of distribution board comprising a type-tested 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 proven during the type-test of the assembly as suitable for such use.
Controlgear (see Switchgear)
Conventional impulse withstand voltage. The peak value of an impulse test voltage at which insulation does not show any disruptive discharge when subjected to a specified number of applications of impulses of this value, under specified conditions.
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.
Danger. Risk of injury to persons (and livestock where expected to be present) from:
(i) fire, electric shock, burns, arcing and explosion arising from the use of electrical energy, and
(ii) mechanical movement of electrically controlled equipment, in so far as such danger is intended to be prevented by electrical emergency switching or by electrical switching for mechanical maintenance of non-electrical parts of such equipment.
Dead not electrically 'live' or 'charged'. (hsg85)
designated competent person: a person appointed by the employer, preferably in writing, to undertake certain specific responsibilities and duties, which may include the issue of permits-to-work. The person must be competent by way of training and qualifications and/or experience. (hsg85)
Design current (of a circuit). The magnitude of the current (rms value for ac.) to be carried by the circuit in normal service.
Device for connecting a luminaire (DCL). System comprising an outlet and a connector providing a fixed luminaire with electrical connection to and disconnection from a fixed installation but not providing, mechanical support for a luminaire.
Direct contact Deleted by BS 7671:2008 (see Basic protection).
Direct heating system. Heating system which generates heat from electrical energy and dissipates it to the room to be heated with a response time being as low as possible.
d.c. systems - see Appendix 9. Mainly about grid tie inverters where AC and DC systems are interconnected.
disconnected: equipment (or a part of an electrical system) that is not connected to any source of electrical energy (hsg85)
Disconnector. A mechanical switching device which, in the open position, complies with the requirements specified for the isolating function.
NOTE 1: A disconnector is otherwise known as an isolator.
NOTE 2: A disconnector is capable of opening and closing a circuit when either a negligible current is broken or made, or when no significant change in the voltage across the terminals of each pole of the disconnector occurs. It is also capable of carrying currents under normal circuit conditions and carrying for a specified time current under abnormal conditions such as those of short-circuit.
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 circuit protective conductors. It may also include signalling and other control devices. Means of isolation may be included in the board or may be provided separately.
Distribution circuit. A circuit supplying a distribution board or switchgear. A distribution circuit may also connect the origin of an installation to an outlying building or separate installation, when it is sometimes called a sub-main.
Distributor. A person who distributes electricity to consumers using electrical lines and equipment that he/she owns or operates.
Double insulation. Insulation comprising both basic insulation and supplementary insulation.
Duct, Ducting (see Cable, ducting).
Earth. The conductive mass of the Earth, whose electric potential at any point is conventionally taken as zero.
Earth electrode. Conductive part, which may be embedded in the soil or in a specific conductive medium, e.g. concrete or coke, in electrical contact with the Earth.
Earth electrode resistance. The resistance of an earth electrode to Earth.
Earth fault current. An overcurrent resulting from a fault of negligible impedance between a line conductor and an exposed-conductive-part or a protective conductor.
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. The earth fault loop comprises the following, starting at the point of fault:
- the circuit protective conductor, and
- the consumer's earthing terminal and earthing conductor. and
- for TN systems, the metallic return path. and
- for TT and IT systems, the Earth return path, and
- the path through the earthed neutral point of the transformer, and
- the transformer winding, and
- the line conductor from the transformer to the point of fault.
Earth leakage current (see Protective conductor current).
Earthed concentric wiring. A wiring system in which one or more insulated conductors are completely surrounded throughout their length by a conductor. for example a metallic sheath. which acts as a PEN conductor.
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 means of earthing.
Electric shock. A dangerous physiological effect resulting From the passing of an electric current through a human body or livestock.
Electrical circuit for safety services. Electrical circuit intended to be used as part of an electrical supply system for safety services.
Electrical source for safety services. Electrical source intended to be used as part of an electrical supply system for safety services.
Electrical supply system for safety services. A supply system intended to maintain the operation of essential parts of an electrical installation and equipment:
(i) for the health and safety of persons and livestock, and
(ii) to avoid damage to the environment and to other equipment.
The supply system includes the source and the circuit(s) up to the terminals of the electrical equipment.
Electrical equipment (abbr: Equipment). Any item for such purposes as generation, conversion, transmission, distribution or utilisation of electrical energy. Such as machines, transformers. apparatus, measuring instruments, protective devices. wiring systems. accessories, appliances and luminaires.
Also defined as ‘electrical equipment’ includes anything used, intended to be used or installed for use, to generate, provide, transmit, transform, rectify, convert, conduct, distribute, control, store, measure or use electrical energy (as defined in the EAW Regulations) (hsg85)
Electrical installation (abbr: installation). An assembly of associated electrical equipment having co-ordinated characteristics to fulfil Specific purposes.
Electrically independent earth electrodes. Earth electrodes located at such a distance from one another that the maximum current likely to flow through one of them does not significantly affect the potential of the other(s).
Electrode boiler (or electrode water heater). Equipment for the electrical heating of water or electrolyte by the passage of an electric current between electrodes immersed in the water or electrolyte.
Electronic convertor (static convertor). A convertor having no moving parts and notably using semiconductor rectifiers.
Emergency stopping. Emergency switching intended to stop an operation.
Emergency switching. An operation intended to remove, as quickly as possible, danger, which may have occurred unexpectedly.
Enclosure. A part providing protection of equipment against certain external influences and in any direction providing basic protection.
Equipment (see Electrical equipment).
Equipotential bonding. Electrical connection maintaining various exposed-conductive-parts and extraneous- conductive-parts at substantially the same potential. (See also Protective equipotential bonding.)
Escape route. Path to follow for access to a safe area in the event of an emergency.
Exhibition. Event intended for the purpose of displaying and/or selling products etc., which can take place in any suitable location, either a room, building or temporary structure.
Exposed-conductive-part. Conductive part of equipment which can be touched and which is not normally live, but which can become live when basic insulation fails.
External influence. Any influence external to an electrical installation which affects the design and safe operation of that installation.
Extra-low voltage (see Voltage, nominal).
Extraneous-conductive-part. A conductive part liable to introduce a potential, generally Earth potential, and not forming part of the electrical installation.
Fairground. Area where one or more stands, amusement devices or booths are erected for leisure use.
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.
Fault protection. Protection against electric shock under single-fault conditions.
NOTE: For low voltage installations, systems and equipment, fault protection generally corresponds to protection against indirect contact, mainly with regard to failure of basic insulation. Indirect contact is "contact of persons or livestock with exposed-conductive-parts which have become live under fault conditions".
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. A cable whose structure and materials make it suitable to be flexed while in service.
Flexible cord. A flexible cable in which the cross-sectional area of each conductor does not exceed 4 mm.
Flexible sheet heating element. Heating element consisting of sheets of electrical insulation laminated with electrical resistance material, or a base material on which electrically insulated heating wires are fixed.
Flexible wiring system. A wiring system designed to provide mechanical flexibility in use without degradation of the electrical components.
Functional earth. Earthing of a point or points in a system or in an installation or in equipment, for purposes other than electrical safety, such as for proper functioning of electrical equipment.
Functional extra-low voltage (FELV). An extra-low voltage system in which not all of the protective measures required for SELV or PELV have been applied.
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.
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 element(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.
Fused connection unit. (FCU) A device associated with the fixed wiring of an installation by which appliances may be connected, and having provision for a replaceable cartridge fuse link.
Gas installation pipe. Any pipe, not being a service pipe (other than any part of a service pipe comprised in a primary meter installation) or a pipe comprised in a gas appliance. for conveying gas for a particular consumer and including any associated valve or other gas fitting.
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.
Hazardous-live-part. A live part which can Give, under certain conditions of external influence, an electric shock.
Heating cable. Cable with or without a shield or a metallic sheath, intended to give off heat for heating purposes.
Heating-free area. Unheated floor or ceiling area which is completely covered when placing pieces of furniture or kept free for built-in furniture.
Heating unit. Heating cable or flexible sheet heating element with rigidly fixed cold tails or terminal fittings which are connected to the terminals of the electrical installation.
High-density livestock rearing. Breeding and rearing of livestock for which the use of automatic systems for life support is necessary.
NOTE: Examples of automatic life support systems are those for \ ventilation. feeding and air-conditioning.
High voltage (see Voltage, nominal). this is defined in national and international standards as being in excess of 1000 V ac or 1500 V dc. However, historically, certain precautions have been applied in the UK to systems energised at more than 650 V ac. To maintain the same degree of safety this guidance uses the term ‘high voltage’ where the voltage exceeds 650 V ac (hsg85)
Highway. A highway means any way (other than a waterway) over which there is public passage and includes the highway verge and any bridge over which. or tunnel through which, the highway passes.
Highway distribution board. A fixed structure or underground chamber, located on a highway, used as a distribution point. for connecting more than one highway distribution circuit to a common origin. Street furniture which supplies more than one circuit is defined as a highway distribution board. The connection of a single temporary load to an item of street furniture shall not in itself make that item of street furniture into a highway distribution board.
Highway distribution circuit. A Band II circuit connecting the origin of the installation to a remote highway distribution board or items of street furniture. It may also connect a highway distribution board to street furniture.
Highway power supply. An electrical installation comprising an assembly of associated highway distribution circuits, highway distribution boards and street furniture, supplied from a common origin.
Hot air sauna. A room or location in which air is heated, in service, to high temperatures where the relative humidity is normally low-. rising only for a short period of time when water is poured over the heater.
Houseboat. Floating decked structure which is designed or adapted for use as a place of permanent residence often kept in one place on inland water.
Indirect contact Deleted by BS 7671:2008 (see Fault protection).
Inspection. Examination of an electrical installation using all the senses as appropriate.
Installation (see Electrical installation).
Instructed person. A person adequately advised or supervised by skilled persons to enable him/her to avoid dangers which electricity may create.
isolated: equipment (or part of an electrical system) which is disconnected and separated by a safe distance (the isolating gap) from all sources of electrical energy in such a way that the disconnection is secure, ie it cannot be re-energised accidentally or inadvertently (hsg85)
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 the isolating function. An isolator is otherwise known as a disconnector.
Ladder (see Cable ladder).
Leakage current. Electric current in an unwanted conductive path under normal operating conditions.
Leisure accommodation vehicle. Unit of living accommodation for temporary or seasonal occupation which may meet requirements for construction and use of road vehicles.
Line 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.
Live: equipment that is at a voltage by being connected to a source of electricity. This implies that, unless otherwise stated, the live parts are exposed so that they can be touched either directly or indirectly by means of some conducting object and that they are either live at a dangerous energy level or dangerous potential, ie over 50 V ac or 120 V dc in dry conditions - see BSI publication PD 6519; (hsg85)
Live conductor (see live part).
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 voltage (see Voltage, nominal).
Live work: work on or near conductors that are accessible and ‘live’ or ‘charge. (hsg85)
Luminaire. Equipment which distributes. Inters or transforms the light transmitted from one or more lamps and which includes all the 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.
NOTE: Lamps includes devices such as light emitting diodes.
Luminaire supporting coupler (LSC). A means, comprising an LSC outlet and an LSC connector. providing mechanical support for a luminaire and the electrical connection to and disconnection from a fixed wiring installation.
LV switchgear and controlgear assembly. A combination of one or more low voltage switching devices together with associated control measuring, signalling, protective, regulating equipment, etc., completely assembled under the responsibility of the manufacturer with all the internal electrical and mechanical interconnection and structural parts. The components of the assembly may be electromechanical or electronic. The assembly may be either type-tested or partially type-tested (see BS EN 60439-1 ).
Main earthing terminal. The terminal or bar provided for the connection of' protective e conductors, including protective bonding conductors, and conductors for functional earthing, if any. to the means of earthing.
Maintenance. Combination of all technical and administrative actions, including supervision actions, intended to retain an item in, or restore it to, a state in which it can perform a required function.
Marina. Facility for mooring and servicing of pleasure craft with fixed wharves. Jetties. piers or pontoon arrangements capable of berthing one or more pleasure craft.
Mechanical maintenance. The replacement, refurbishment or cleaning of lamps and non-electrical parts of equipment, plant and machinery.
Mobile and offshore installations. Installations used for the exploration or development of liquid or gaseous hydrocarbon resources.
Mobile equipment (portable equipment (deprecated)). Electrical equipment which is moved while in operation or which can easily be moved from one place to another while connected to the supply.
Mobile home. A transportable leisure accommodation vehicle which includes means for mobility but does not meet the requirements for construction and use of road vehicles.
Monitoring. Observation of the operation of a system or part of a system to verify correct functioning or detect incorrect functioning by measuring system variables and comparing the measured values with specified values.
Motor caravan. Self-propelled leisure accommodation vehicle, used for touring, that meets the requirements for the construction and use of road vehicles.
NOTE: It is either adapted from a series production vehicle, or designed and built on an existing chassis. with or without the driving cab.. the accommodation being either fixed or dismountable.
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.
Nominal voltage (see Voltage, nominal).
Obstacle. A part preventing unintentional contact with live parts but not preventing deliberate contact.
Open-circuit voltage under standard test conditions Uoc STC. Voltage under standard test conditions across an unloaded (open) generator or on the d.c. side of the convertor.
Ordinary person. A person who is neither a skilled person nor an instructed person.
Origin of an installation. The position at which electrical energy is delivered to an electrical installation.
Origin of the temporary electrical installation. Point on the permanent installation or other source of supply from which electrical energy is delivered to the temporary 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.
PELV (protective extra-low voltage). An extra-low voltage system which is not electrically separated from Earth, but which otherwise satisfies all the requirements for SELV.
PEN conductor. A conductor combining the functions of both protective conductor and neutral conductor.
Phase conductor (see Line conductor).
Pleasure craft. Any boat, vessel, yacht, motor launch, houseboat or other floating craft used exclusively for sport or leisure.
Plug. Accessory having pins designed to engage with the contacts of a socket-outlet, and incorporating means for the electrical connection and mechanical retention of a flexible cable or cord.
Point (in wiring). A termination of the fixed wiring intended for the connection of current-using equipment.
Portable equipment (see Mobile equipment).
Powertrack. A system component, which is a generally a linear assembly of spaced and supported busbars, providing electrical connection of accessories.
Powertrack system (PT system). An assembly of system components including a powertrack by which accessories may be connected to an electrical supply at one or more points (pre-determined or otherwise) along the powertrack.
NOTE: The maximum current rating of a powertrack system is 63A.
Protective bonding conductor. Protective conductor provided for protective equipotential bonding
Protective conductor (PE). 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.
Protective conductor current. Electric current appearing in a protective conductor, such as leakage current or electric current resulting from an insulation fault.
Protective earthing. Earthing of a point or points in a system or in an installation or in equipment for the
Protective equipotential bonding. Equipotential bonding for the purposes of safety.
Prospective fault current (Ipt). 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 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 2.4).
Protective separation. Separation of one electric circuit from another by means of:
(i) double insulation, or
(ii) basic insulation and electrically protective screening (shielding), or
(iii) reinforced insulation.
PV. Solar photovoltaic.
PV a.c. module. Integrated module/invertor assembly where the electrical interface terminals are a.c. only. No access is provided to the d.c. side.
PV array. Mechanically and electrically integrated assembly of PV modules, and other necessary components. to form a d.c. power supply unit.
PV array cable. Output cable of a PV array.
PV array junction box. Enclosure where PV strings of any PV array are electrically connected and where devices can be located.
PV cell. Basic PV device which can generate electricity when exposed to light such as solar radiation.
PV d.c. main cable. Cable connecting the PV generator junction box to the d.c. terminals of the PV invertor.
PV generator. Assembly of PV arrays.
PV generator junction box. Enclosure where PV arrays are electrically connected and where devices can be located.
PV installation. Erected equipment of a PV power supply system.
PV invertor. Device which converts d.c. voltage and d.c. Current into a.c. voltage and a.c. current.
PV module. Smallest completely environmentally protected assembly of interconnected PV cells.
PV string. Circuit in which PV modules are connected in series, in order for a PV array to generate the required output voltage.
PV string cable. Cable connecting PV modules to form a PV string.
PV supply cable. Cable connecting the a.c. terminals of the PV invertor to a distribution circuit of the electrical installation.
Rated current. Value of current used for specification purposes, established for a specified set of operating conditions of a component, device, equipment or system.
Reduced low voltage system. A system in which the nominal line to line voltage does not exceed 110 volts and the nominal line to Earth voltage does not exceed 63.5 volts.
Reinforced insulation. Single insulation applied to live parts, which provides a degree of protection against electric shock equivalent to double insulation under the conditions specified in the relevant standard. The term `single insulation' does not imply that the insulation must be one homogeneous piece. It may comprise two or more layers which cannot be tested singly as supplementary or basic insulation.
Reporting. Communicating the results of periodic inspection and testing of an electrical installation to the person ordering the work.
Residences and other locations belonging to agricultural and horticultural premises. Residences and other locations which have a conductive connection to the agricultural and horticultural premises by either protective conductors of the same installation or by extraneous-conductive-parts.
NOTE: Examples of other locations include offices, social rooms, machine-halls, workrooms, garages and shops.
Residential park home. A factory produced relocatable dwelling designed for permanent residence which may be used for leisure purposes.
Residual current. Algebraic sum of the currents in the live conductors of a circuit at a point in the electrical installation.
Residual current device (RCD). 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 current operated circuit-breaker with integral overcurrent protection (RCBO). A residual current operated switching device designed to perform the functions of protection against overload and/or short-circuit.
Residual current operated circuit-breaker without integral overcurrent protection (RCCB). A residual current operated switching device not designed to perform the functions of protection against overload and/or short-circuit.
Residual operating current. Residual current which causes the RCD to operate under specified conditions.
Resistance area (for an earth electrode only). The surface area of ground (around an earth electrode) on which a significant voltage gradient may exist.
Response time The time that elapses between the failure of the normal power supply and the ability of the auxiliary power supply to energize the equipment.
Restrictive conductive location (see Conducting location with restricted movement).
Ring final circuit. A final circuit arranged in the form of a ring and connected to a single point of supply.
Safety service. An electrical system for electrical equipment provided to protect or warn persons in the event of a hazard, or essential to their evacuation from a location.
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 (see 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.
Short-circuit current under standard test conditions 1sc STC. Short-circuit Current of a PV module, PV string, PV array or PV generator under standard test conditions.
Show. Display or presentation in any suitable location, either a room, building or temporary structure.
Simple separation. Separation between circuits or between a circuit and Earth by means of basic insulation.
Simultaneously accessible parts. Conductors or conductive parts which can be touched simultaneously by a person or, in locations specifically intended for them. by livestock.
NOTE: Simultaneously accessible parts may be: live parts. exposed-conductive-parts, extraneous-conductive-parts, protective conductors or earth electrodes.
Skilled person. A person with technical knowledge or sufficient experience to enable him/her to avoid dangers which electricity may create.
Socket-outlet. A device. provided with female contacts, which is intended to be installed with the fixed wiring, and intended to receive a plug. A luminaire track system is not regarded as a socket-outlet system.
Spur. A branch from a ring or radial final circuit.
Stand. Area or temporary structure used for display, marketing or sales.
Standard test conditions (STC). Test conditions specified in BS EN 60904-3 for PV cells and PV modules.
Standby electrical source. Electrical source intended to maintain, for reasons other than safety, the supply to an electrical installation or parts or a part thereof; in case of interruption of the normal supply.
Standby electrical supply system. Supply system intended to maintain, for reasons other than safety, the functioning of an electrical installation or parts or a part thereof, in case of interruption of the normal supply.
Static convertor. A convertor having no moving parts and notably using semiconductor rectifiers.
Stationary equipment. Electrical equipment which is either fixed, or equipment having a mass exceeding 18 kg and not provided with a carrying handle.
Street furniture. Fixed equipment located on a highway.
NOTE: Street furniture includes street located equipment.
Street located equipment. Fixed equipment located on a highway, the purpose of which is not directly associated with the use of the highway.
Supplementary insulation. Independent insulation applied in addition to basic insulation for fault protection.
Supplier (see Distributor).
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.
Switch-disconnector. A switch which, in the open position, satisfies the isolating requirements specified for a disconnector.
NOTE: A switch-disconnector is otherwise known as an isolating switch.
Switchboard. An assembly of switchgear with or without instruments. but the term does not apply to groups of local switches in final circuits.
Switchgear. An assembly of main and auxiliary switching equipment for operation, regulation, protection or other control of an electrical installation.
System. An electrical system consisting of a single source or multiple sources running in parallel of electrical energy and an installation. For certain purposes of the Regulations. types of system are identified as follows, depending upon the relationship of the source, and of exposed-conductive-parts of the installation, to Earth:
TN system. A system having one or more points of the source of energy directly earthed, the exposed- conductive-parts of the installation being connected to that point by protective conductors.
TN-C system. A system in which neutral and protective functions are combined in a single conductor throughout the system (see Figure 2?).
TN-S system. A system having separate neutral and protective conductors throughout the system (see Figure 2.3).
TN-C-S system. A system in which neutral and protective functions are combined in a single conductor in part of the system (see Figure ?.4).
TT system. A system having, one point of the source of energy directly earthed, the exposed-conductive- parts of the installation being connected to earth electrodes electrically independent of the earth electrodes of the source (see Figure 2.5).
IT system. A system having no direct connection between live parts and Earth, the exposed-conductive- parts of the electrical installation being earthed (see Figure 2.6).
Multiple source and d.c. systems - see Appendix 9.
Temporary electrical installation. Electrical installation erected for a particular purpose and dismantled when no longer required for that purpose.
Temporary structure. A unit or part of a unit, including mobile portable units, situated indoors or outdoors, designed and intended to be assembled and dismantled.
Temporary supply unit. An enclosure containing equipment for the purpose of taking a temporary electrical supply safely from an item of street furniture.
Testing. Implementation of measures to assess an electrical installation by means of which its effectiveness is proved. This includes ascertaining values by means of appropriate measuring instruments, where measured values are not detectable by inspection.
Thermal storage floor heating system. Heating system in which, due to a limited charging period, a restricted availability of electrical energy is converted into heat and dissipated mainly through the surface of the floor to the room to be heated with an intended time delay.
Trunking (see Cable: trunking).
Verification. All measures by means of which compliance of the electrical installation with the relevant requirements of BS 7671 are checked, comprising of inspection, testing and certification.
Voltage bands
Band I
Band I covers:
- installations where protection against electric shock is provided under certain conditions by the value of voltage:
- installations where the voltage is limited for operational reasons (e.g. telecommunications, signalling, bell, control and alarm installations).
Extra-low voltage (ELV) Will normally fall within voltage Band I.
Band II
Band II contains the voltages for supplies to household and most commercial and industrial installations.
Low voltage (LV) will normally fall within voltage Band II.
NOTE: Band II voltages do not exceed 1000 V a.c. rms or 1500 V d.c.
Voltage, nominal. Voltage by which an installation (or part of an installation) is designated. The following ranges of nominal voltage (rms values for a.c.) are defined:
- Extra-low. Not exceeding 50 V a.c. or 120 V ripple-free d.c., whether between conductors or to Earth.
- Low. Exceeding extra-low voltage but not exceeding 1000 V a.c. or 1500 V d.c. between conductors, or 600 V a.c. or 900 V d.c. between conductors and Earth.
- High. Normally exceeding low - voltage.
NOTE: The actual voltage of the installation may differ from the nominal value by a quantity within normal tolerances.
Voltage, reduced (see Reduced low voltage system).
Wiring system. An assembly made up of cable or busbars and parts which secure and, if necessary, enclose the cable or busbars.