Electrical Terminology – Jargon Explained

17th Edition BS7671 : 2008 Requirements for Electrical Installations IEE Wiring Regulations 17th Edition

These regulations apply to the design, erection and verification of electrical installations including additions and changes. Installations done to earlier editions will probably not comply with the 17th in every respect. This does not always mean they are unsafe or require upgrading but there will usually be benefits in doing so.


A general term applied to most of the devices used for connecting and controlling lighting and power, eg sockets and switches.

BS – British Standard (General)

A publication of the British Standards Institution (BSI). Each one is numbered, starting with the letters BS, and defines the standard of a product. The number given to the Requirements for Electrical Installations (IEE Wiring Regulations) is BS7671. Some British Standards are being harmonised with European Standards and carry the

BS 7671

See 17th Edition

Buy With Confidence

This is a scheme run by some County Council Trading Standards Departments including Kent. It provides details of reliable local trades people who have been checked for trust worthiness. Trading Standards Officers visit and vet every applicant and carry out stringent checks including compliance with consumer protection laws. Members are monitored by the Trading Standard Service to ensure that standards are maintained and customers are invited to provide feedback.

Members are required to deal with any complaints in a professional manner if a problem cannot be resolved the Trading Standards Service will attempt to help in reaching a solution.

Roger J Goldfinch is a member of this scheme.


A plastic or steel strip used to protect cables when plastering a flush installation. Capping is marginally cheaper than conduit, but conduit is preferred as alterations are easier.


Document giving details of an electrical installation issued by the installer on completion of the work.


A channel cut into a wall to conceal a cable. We always use a tube (conduit) to protect the cable when it is put in and to make replacing the cable easier. Our policy  is to carry out making good unless otherwise instructed.


A length of cable, plus equipment connected to a single protective device.

Circuit Breaker

An automatic safety switch which will turn off the electrical supply when there is a fault.

Class 1 Equipment

Has exposed metal parts which need to be earthed, eg washing machines & microwaves.

Class 2 Equipment

Either has no exposed metal parts, or those it does have do not need to be earthed because there is extra protection within the equipment, eg televisions & most vacuum cleaners.

Competent Person

A person who possesses the technical knowledge, skill and experience to carry out the work needed safely and effectively.

Completion Certificate

An old term for Electrical Installation Certificate, no longer used.


A plastic or metal tube used to enclose and protect cables. It may be oval or round and installed flush or surface.

CPC – Circuit Protective Conductor

A safety earthing wire run as part of a circuit to connect all parts which need to be earthed to the earth (often loosely known as an earth wire).

CU – Consumer Unit

Still often known as a ‘fusebox‘, the modern consumer unit contains a variety of circuit breakers able to provide a much higher level of protection than fuses. Most properties will have a single CU and this is the point from which electricity is distributed throughout the property.

Cut out

Cut out is the box where incoming the incoming cable from the electricity board is terminated, if your supply is overhead you may have a number of smaller boxes rather than a single large one. It contains electricity boards fuses, should be in good condition and sealed.

Most domestic supplies are now 100amp single phase but if you have an older property your main fuse will probably be less than 100 amp. If you use electricity a lot it is worth getting your load assessed to see how much you use, with a view to upgrading the cut out to 100amp to avoid possible nuisance failure. If you upgrade your cut out you are usually putting in a fuse that will allow you to drawn down 100amp.

Naturally your own equipment should also be able to take the higher load and we would assess that at the same time.

Dado Trunking

A  cable covering run at desk height and large enough to include accessories, eg a socket. It is usually multi compartment so that cabling can be run through it.

Changes to the lay out within an existing run can be made quickly and easily.


There will be a charge for labour and materials used where either a price is not needed, there is not enough time to prepare one or it is not practical to give one due to unknown elements of work. Fault finding is a typical example and the time taken to locate the fault will often be longer than the time to fix it.

Disconnection Time

The wiring regulations specify how quickly a protective device should operate and disconnect the supply when a fault occurs. The time varies in different circumstances but is specified to ensure that neither the installation nor those in contact with it are harmed.

DB – Distribution Board

An enclosure (box) containing protective devices (fuses/mcb‘s) for a number of circuits in large premises.


Light fittings recessed into a ceiling – available in many forms using a variety of lamps including the most recent energy saving types.

Earth Rod

A metal rod driven into the ground to provide an independent means of earthing, an installation when the Regional Electricity Company cannot provide an earthing facility.


Metal parts of your electrics or appliances may become electrically charged (live) if there is a fault. The purpose of earthing is to minimise the risk to anyone touching those metal parts when there is a fault.

This is achieved by connecting the metal parts to earth (the ground) providing a path for fault current to flow safely to earth.

The path needs to be of a low enough resistance for the current flow to operate a protective device and disconnect the circuit before the situation becomes dangerous.

Economy 7

The most common variable rate metering tariff which gives a reduced price for 7 hours overnight.

Primarily used to night storage heating it will also provide cheaper energy for all other appliances in use at the same time.

Electrical Installation

A term usually applied to the complete electrical system within a building.

Electrical Installation Certificate

A certificate denoting the responsible person(s) for the design, construction and testing of the electrical installation it refers to. It is not complete without the schedule of inspections and the schedule of tests and results.

ELV – Extra Low Voltage

Voltage not exceeding 50v a.c or 120v ripple free d.c whether between conductors or to earth. Commonly a nominal 12v as used for many downlighters and 3-12v for bells and chimes.


An estimate is an approximate price given either as a range of a percentage variation and constitutes an offer to do the work within the stated limits. It is used where an exact price is not required or there is inadequate information to give one.

Extension Lead

A flexible cord with a plug on one end and one or more sockets on the other.

Note – They are often misused, including overloading. Ideally they should be restricted to short term use and frequently checked for condition. Putting in more fixed sockets is better than long term use of extension leads.

FET – Fixed Equipment Testing

Testing of equipment which cannot be or is not moved in normal use, eg showers and cookers.

It is often forgotten – falling between testing of the main electrical installation and portable appliance testing.

Fire alarm

A system which will produce a loud and distinctive sound to alert all people in the area. It may be triggered manually by a person who sees the fire pressing a call point or automatically by a smoke or heat detector.

To be effective it should be professionally designed, installed and maintained.

Flex – Flexible cord

Flex has fine stranded conductors allowing a lot of movement without damage and is necessary for portable applications – e.g. kettles.

The wiring regulations allow flex to be used for fixed wiring but it can be difficult to connect in terminals not designed for it.

Flush – Flush fitted

Cable and back boxes for accessories (e.g. sockets) are set within the fabric of the building. Unless there are existing conduits or voids for running the cables chasing will be required.


A protective device incorporating a wire of specially designed link which melts (blows) under fault conditions.

A re-wireable (semi-enclosed) fuse may be fitted with a new piece of wire to ‘mend’ it provided the correct size of wire is used and the carrier is in good condition.

Cartridge fuses come in a wide range of types and sizes – the most common being in the 13A plug. They must always be replaced (rather than mended) and always with the same type as the original. Under no circumstances should any attempt be made to ‘mend’ a cartridge fuse.

Where an installation is not under the supervision of skilled staff circuit breakers are now preferred.

Fuse box

See – Consumer Unit.

Fused Connection Unit

An accessory (the same size as a light switch) incorporating a fuse the same size as in a 13A plug. It may be used to feed a wide variety of equipment by flex or cable.

Fused Spur

See – Fused Connection Unit

HMO – House in Multiple Occupation

A property let to three or more tenants who form two or more households.

IEE Wiring Regulations

See 17th Edition.


See – Electrical Installation

Landlords Certificate

There is no specific landlords certificate (such as the one used in the gas industry) because the wiring regulations are the same whether the property is rented or owner occupied.

Please refer to the section on NICEIC Wiring Certificates and to the Electrical Safety Council websites www.esc.org.uk – Landlords guide to Electrical Safety.

LV – Low Voltage

A commonly misused term and often used to refer to a voltage lower than the nominal 230volt supply.

However the normal mains supply of 230volt is officially ‘low voltage’.

MA – Milliamps

A unit of electrical current (flow) which you are most likely to encounter with RCDs their operating parameters are specified in mA.

The most common is 30mA and this is designed to give protection against a potentially lethal shock by switching off so quickly that no harm comes to the individual.

Main Bonding

Connecting all services and structural steel which may form a path to earth to the Main Earthing Terminal of an installation.

Mains – Mains Electricity

The electricity  supplied to the end user at nominal 230volt single phase (see Three Phase)

There are bound to be fluctuations on the supply but the network operator has a duty to keep these within specified limits. At present these are 216.2v and 253v. This variation can have a significant effect on the functioning and the life some equipment.

Making Good

Restoring the fabric of the building similar to that existing prior to the works. This does not usually include re-decoration. See Terms and conditions.

MCB – Miniature Circuit Breaker

An automatic switch which will turn off under specific fault conditions. It may be regarded as the modern equivalent of a fuse but giving simpler and better protection. It can be switched back on when the fault is cleared and, unlike a fuse, it cannot easily be replaced with the wrong wire.

MCCB – Moulded Case Circuit Breaker

Larger versions of Miniature Circuit Boards and only found in industrial or commercial installations.

MET – Main Earth Terminal

The connector at the origin of your installation to which all the earthing cables are connected. In modern installation it is usually inside the CU or DB.

Mini Trunking

A plastic cable enclosure system for surface installation.

It has a clip on lid, is usually square or rectangular (in sections) and used for it neat appearance (especially when two or more cables are run together).

Minor Works Certificate

This should be issued for minor modifications to a circuit or circuits. If a new circuit is added then an Electrical Installation Certificate should be used.

NICEIC – The National Inspection Council for Electrical Installation Contracting.

The NICEIC is an independent consumer safety organisation and has been the industries voluntary regulatory body for electrical safety matters for more than 50 years.

The NICEIC is an impartial body that consumers can trust because it puts safety first. It maintains a register (or roll) of electrical contractors who it has assessed for standards of work, premises, equipment, documentation and key supervisory staff.

All contractors on the roll are reassessed annually to ensure they are still up to standard.

Enrollment is voluntary but contractors who are competent and conscientious about their service consider it important to enrol. In the unlikely event of any dispute over the standard of work the client can seek resolution through the NICEIC.

Roger J. Goldfinch has been on the roll since 1981 and has open approval to carry out all types of work.

Observations & Recommendations

Observations note deviations from current standards when carrying out an inspection and test of an electrical installation.

Each item carries a recommendation number (currently 1-4) indicating its importance and the urgency of an action required.

As part of our customer service we link this directly to a schedule of recommended remedial work and a quotation so that all necessary information is presented together.

Some observations may not relate to deviations from current standards but deviations from good practice and are included for advice.

Off Peak

The lower tariff (often night time) cost of electricity.

Over current – Cable

Current exceeding the rated value.

Note – This is not fixed for a particular cable and will depend upon a number of factors. Outlets selling electrical installation materials will not usually be able to tell you what cable to use for a specific purpose because they do not have the necessary information on your property yo carry out the calculations required, nor are they usually qualified to do so.

Part P

See – Part P & Other Building Requirements Section.

Partial Rewire

Indicates that some wiring is retained while some is replaced. Commonly this is required for properties built in the early sixties with no CPC (Circuit Protective Conductor) in the lighting circuits when use of metal fittings presents a real danger.

PAT – Portable Appliance Testing

PAT is necessary if you need to show you have done all you can to prevent danger to those using the equipment.

If you are an employer or a landlord you will almost certainly have some responsibility in this field. Frequency of testing will depend upon the nature and location of equipment.


Photocell is a light operated switch, usually providing control for lighting to switch on at dusk and off at dawn. Security lights operated by a PIR will incorporate a photocell so that they only work at night.

PIR – Passive Infra-Red

A PIR is a sensor and a switch. The sensor detects a moving heat source and operates the switch, usually for a set period of time.

PIR’s are used for alarm systems and internal lighting control but also for security lighting. In that application they will incorporate a photocell to avoid day time operation.

Care needs to be taken in selection, sighting and installation to achieve the desired result.

PIR – Periodic Inspection Report

A Periodic Inspection Report is a certificate detailing the schedule of circuits, tests, limitations and observations made by a qualified electrician. It is usually used when there is

(1) A change of use of the building

(2) a fire/flood/other damage has occurred and the extent of the damage to the wiring is required

(3) regular maintained records of the installation’s condition are required

(4) to assess the general condition of a property’s electrical installation prior to e.g sale or rental.

See also – Certificates

PME – Protective Multiple Earthing

An earthing arrangement commonly employed by the Regional Electricity Company on their distribution network to be able to provide the consumer with a terminal for earthing their installation.

If not available earth rod required.



Protective Device

Usually a fuse or circuit breaker installed to protect life and/or property in the event of a fault by disconnecting the power supply.

Provisional Sum

A provisional sum is an allowance made for a specific part of the work when there is inadequate information to include a fixed price for it. The sum is chosen with care but the final cost may vary considerably. An estimate or a quotation should be obtained when more information is available.


A quotation is an offer to do the work specified at the fixed price given.

QS – Qualified Supervisor

Every contractor on the NICEIC roll must have at least one QS who has been assessed and approved to supervise the work of other staff.

They are subject to review on every annual inspection to ensure standards are maintained.


A radial circuit is a circuit with one point source of power and one or more accessories attached in a daisy chain. All circuits in the UK are radials except for some socket circuits which are often in the form of a ‘ring’.


A document issued following the inspection and test of an electrical installation and may be compared with the MOT on a car. To maintain an installation in good order it is important to carry out regular inspections. Recommended intervals vary depending on the type of installation.

RCBO – Residual Current Breaker with Over-current (Protection)

A single device incorporating the features of both MCB (Miniature Circuit Breaker) and RCD (Residual Current Device). RCBO’s are used to give the best possible protection to individual circuits and avoid the nuisance caused when an earth fault trips an RCD protecting a bank of MCBs.


See – RCD

RCD – Residual Current Device

Residual Current Device is a blanket term covering many applications. It monitors the feed and return currents at a given point – they should be equal. The RCD will switch off if they are not equal or very nearly so. Any imbalance is the result of the current leaking to earth.

One form  has often been fitted as the main switch for an installation (RCCB – Residual Current Circuit Breaker without Over current Protection) but this is now considered bad practice because of the inconvenience when it trips under fault and power is lost to everything at once.

At the other end of the scale an RCD may be incorporated into a socket (SRCD) or it may be portable (PRCD) either a as a plug or an adaptor.

See also – RCBO & MA

Rewire – Full Rewire

Complete replacement of an installation which may be required for three reasons.

1)    The existing is all in poor condition

2)    The majority of the existing is in poor condition and it is in poor condition and it is uneconomic to retain parts of the existing which may in themselves be satisfactory.

3)    Clients requirements for alterations and additions cannot be carried out economically.

A rewire enable the layout and provision to be improved and provides a 10 Year Electrical Installation Certificate.

Note – Our 10 Year Guarantee for Peace of Mind.

Ring – Ring Final Circuit

Circuit arranged in the form of a complete ring fed with the final two ends connected to a single protective device. Spurs may be fed from the ring within strictly specified limits.

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.


Three different types of shower are electrically different too. Power showers are fed from the hot and cold water systems and the electrical part is usually a spur to feed the electrical pump which adds water pressure.

1)    Electric shower – takes cold water at the mains pressure and use an element within the shower to instantaneously provide the user with hot water.

2)    Power shower – takes hot water from an external source plus cold water at the same pressure and uses a small electrical pump as a boost.

3)    Mixer shower – takes hot and cold water and simply mixes them with no electrical components.

Skirting Trunking

Similar to dado trunking but at floor level.

Smoke Alarm

A single unit incorporating a sensor unit to detect smoke and a sounder to alert occupants. It may be powered from a mains supply, a battery or both.

A heat alarm is used where a smoke alarm would be prone to false alarms and is commonly included under the heading of smoke alarm.

There are too many variations of smoke alarm to detail here but call us and we can talk to you.

Smoke Alarm System

A number of alarms linked so that when one is triggered they all sound at once so that you can hear it where ever you are (and have the best chance of escape).


A broad term covering any light which is directional from a relatively small source. They may be recessed or surface mounted (including on a track) and use a wide variety of light sources to suit the application.

Ref. To energy efficient lamps.


Part of a ring final cut which is not a section of the main ring. Often used as an economical way to make additions to a ring, avoiding the need to break into and modify the ring itself.

Spurs from the ring may be fused or un-fused. An un-fused spur may only feed one point.


See – RCD

Sub Main

A Sub Main is a distribution cable used to supply a consumer unit or distribution board remote from the intake position. Usually only found in larger premises where it becomes impractical and expensive to run every circuit all the way to the intake.  It may be used to feed the new part when a building is extended.

Supplementary Equipotential Bonding

Connections made between items of exposed metal work within a specific area to ensure that it is not possible to get a shock from them because of a voltage difference between them.

Surface (as opposed to Flush)

Is a term used to describe an installation carried out on (the faces of) the structure where cables are enclosed in mini trunking or fixed using clips.  The back boxes for the accessories are also visible.

Switched Fused Spur

A fused connection unit but with a switch on it.

Three Phase

All public power generation is three phase because it is cheaper to transmit and this carries through most of the distribution system. When the supply to consumers is on poles overhead it can be identified by four wires on the poles. Three of these are the phase (live) wires and the fourth is the common return (neutral) wire.

Most domestic properties only use one of the three phases plus the neutral to give what is known as a single phase supply. You can see that in the event of a supply network fault it would be possible for some properties in a road to have electricity while others did not because they take supply from different phases and the fault does not necessarily affect all three.

From the point of view of generation and distribution it is desirable for the load on the three phases to be as equal as practicable. For larger consumers a three phase supply is always provided and the load balanced between them.

Some equipment is specifically designed to work on three phase (three phase motors are more efficient than single phase ones and there is a limit on the use of single phase machines available). Single phase equipment can always be used on a three phase supply – it just uses one of them!

If you have a three phase motor but only a single phases supply you may be tempted by a complex box of tricks designed to make your motor believe it has a three phase supply. Our advice is don’t be tempted because it doesn’t always work well – if at all. It is far better to use all equipment on a supply it was designed for.


A cable enclosure system with removable lid. It is available in steel and plastic in various profiles for all kinds of applications from domestic to heavy industrial.

Trust Mark

Trust Mark is a Government Endorsed Scheme to help you find a reliable trades person. When you see the Trust Mark logo you know that:

The approved scheme operators have checked the firm’s technical skills, trading record and financial position;
The firm has signed up to a code of practice that includes insurance, good health and safety practices, and customer care;
Our approved scheme operators have checked and will continue to monitor the quality of work, trading practices and customer satisfaction;
The firm will tell you about any building regulations you must meet, and may be able to give you the certificates you need;
If you have a problem or disagreement with the firm, there will be a clear and user friendly complaints procedure to help sort out the problem; and
If the firm doesn’t automatically provide insurance cover, you will have the option to buy a warranty in case it goes out of business.

In return you are expected to deal fairly with the firm, agree a fair price for good work and pay quickly when the job is finished.

Roger J. Goldfinch is registered on the Trust Mark Scheme through the NICEIC.

U/S – Unserviceable

Unserviceable means that the item is broken, damaged or in some other way does not fulfil the function it was intended to when it was manufactured.

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