Measurement of current.


The thin metal or plastic channel sometimes used to contain cables when fixed to a wall before plastering. Capping is used to make it easy to run several cables following the same route with the minimum use of fixings. It does not provide protection against damage from nails or screws.


This involves making a slot to install cables or wiring systems into solid walls. Chasing causes a lot of disruption and once completed will require making good.


An assembly of electrical equipment (e.g. socket outlets, lighting points and switches) supplied from the same origin and protected against overcurrent by protective device(s).

Circuit breaker or MCB (mini circuit breaker):

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

Consumer unit:

Also known as a fusebox. This is a particular type of distribution board comprising a co-ordinated assembly for the control and distribution of electrical energy principally in domestic premises. It incorporates manual means of double-pole isolation on the incoming circuit(s) and an assembly of one or more fuses, MCBs, RCDs and other devices purposely manufactured for such use.


A flow of electric charge or the rate of flow of electric charge.

Distribution board:

An assembly containing switching or protective 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.

Double pole switch:

Isolates two parts of the circuit at the same time.


Earthing minimises the risk of receiving an electric shock if you should touch metal parts when a fault has occurred. It provides a path for the faulty current to flow safely to earth, which causes the protective device (MCB, fuses) to disconnect the circuit and stop the danger. The electrician will check that the earthing and bonding is satisfactory before starting any work.

Earth bonding:

The process for linking together exposed metal parts such as water pipes within a property.

Electrical installation certificate (EIC):

A safety certificate issued by an electrician when they complete any new electrical work, or changes to existing electrics. The certificate confirms that the work has been designed, built, inspected and tested to the UK national standard BS 7671.

Electrical installation condition report (EICR):

A report on the condition of your electrical wiring, containing an overall assessment of the safety of the wiring, observations on its condition, and a number of recommendations (in order of priority) for action (if any is required) to restore the wiring to a satisfactory condition for continued safe use — formerly known as a periodic inspection report (PIR).

Fused connection unit:

Enables electricity to be supplied to an item of equipment or appliance providing its own method of circuit protection (by fuse), and sometimes includes a switch. Fused connection units are sometimes referred to in the electrical trade as fused spurs.

Main bonding:

Connecting metal pipes (gas, water or oil) entering a home or building to the main earthing terminal of the electrical installation via low-resistance conductors.

Miniature circuit breaker (MCB):

Commonly known as a circuit breaker. An automatic protective device fitted in the fusebox that will disconnect a circuit if there is a fault or overload.

Mini trunking:

A plastic enclosure with one removable side that is used to install cables on the surface of walls and ceilings.

Minor works certificate:

A safety certificate (see electrical installation certificate, above) used when an addition or alteration is made to your electrics and no new circuits have been added.


Electrical current (in amps) that exceeds the maximum limit of a circuit. May result in risk of fire or shock from insulation damaged from heat generated by an overcurrent condition.

Part P:

The specific section of the Building Regulations for England and Wales which relates to electrical installations in domestic properties.

PAT (portable appliance testing):

Inspection and testing of electrical equipment including portable appliances, moveable equipment, hand- held appliances, stationary equipment, fixed equipment/appliances, IT equipment and extension leads. But predominately in commercial situations.

Residual current device (RCD):

This is a sensitive switching device that trips a circuit when an earth fault is detected. RCD protection is particularly important for socket circuits that may be used to supply portable equipment for use outdoors.


A full rewire should mean that all parts of the electrics – that is cables, circuits and accessories – are new. A partial rewire is a common situation if it’s not possible or necessary to fully rewire all the electrics, for example, when existing cabling is suitable for continued use (this minimises the degree of damage and disruption), or where only a part of the electrics has suffered damage from a burst water pipe or similar.

Ring or ring main:

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

Separated extra-low voltage (SELV):

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 – 12V (volt) – lighting transformers and shaver points.


An additional electrical connection often taken from a point on the existing electrical circuit, such as a socket. It may provide a supply to a new socket or a fused connection unit.

Supplementary bonding:

Connecting together metal parts of electrical equipment (such as a heated towel rail) and the metal parts of a non-electrical item (such as water pipes) to prevent a dangerous voltage between them, if a fault occurs. May be required in bath and shower rooms.


Transforms one voltage into another.

Voltage and extra-low voltage:

Voltage is the force behind electricity. It can be referred to as electric pressure and compared with the water pressure in a plumbing system. Another term for voltage is EMF (electromotive force). Voltage appears across components and current flows through them.

  • Extra low: means normally not exceeding 50V (AC).
  • Low: exceeding 50V (AC) but not exceeding 1,000V (AC).
  • High: exceeding 1,000V (AC).

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