This jargon buster or glossary of electrical terms contains some examples of the definitions commonly used in electrical engineering and technology. It is not a complete list of all the words you might encounter and is intended to act as a quick reference guide and aide memoire.
AC [Alternating Current]
Electrical current which is alternating backwards and forwards, like mains electricity which alternates at 50Hz.
Ampere [A or Amps]
The base SI unit (international standard) for the measurement of electrical current, equivalent to one coulomb per second.
Bonding (Main & Supplementary)
Main Bonding connects services containing extraneous conductive parts like water and gas to the installations MET. Supplementary Bonding connects metalwork & electrical equipment together.
Breaker (Circuit) *See: MCB
BS [British Standard]
Standards set out by the British Standard Institute (BSI), most equipment and regulations have a unique BS number and therefore a standard, these standards should be met/used by all installers and companies alike.
BS EN [British Standard European Harmonised]
BS EN is a British standard that has been harmonised with European standards, they must not differ from one another.
BS7671:2008 * aka The Regulations & 17th Edition
A British standard you will come into contact with frequently within the electrical industry. It details all the standards that should be met in current electrical installations and is currently on its 17th revision and 3rd amendment; IEE Wiring Regulations (BS 7671:2015).
CCU [Consumer Control Unit] * aka Distribution Board * Fuse Board
This is usually found at the origin of electrical supply in a residential installation, it contains all the circuit breakers, main isolation and usually the MET.
Simply, a circuit is a path between two or more points along which an electrical current can be carried. A circuit must be complete loop or electricity cannot flow.
Circuit Breaker *See: MCB
A device which is used for the protection of the circuit’s conductors and under single fault conditions disconnects the circuit’s electrical supply at the origin. NB: it’s not there to primarily protect people but protect the circuit!
City & Guilds
A qualification awarding body, all electrical professionals should be qualified and educated to proper and recognised qualification bodies.
Consumer Unit *See: CCU & Distribution (board)
Usually refers to industrial types of containment for electrical cables such as; trunking, Conduit, Cable Tray and cable basket, generally containment is metallic, however it can also be plastic.
A test performed between two points to ensure continuous electrical conductivity, and that conductivity is of a sufficiently low level.
The SI unit for a measure of electrical charge and is approximately equal to the charge of 6.24151 × 1018 electrons.
CPC [Circuit Protective Conductor]
The name of an earth wire when contained in a final circuit.
The flow of electric charge measured in Amperes.
DC [Direct Current]
Electrical current which is constant and flows in one direction, like from a battery.
Distribution Board *aka CCU in residential
Typically a wooden board or electrical cabinet consisting of an installation’s circuit breakers, MET and incoming supply. In very large installations it would be common to have large distribution board connected to smaller distribution boards.
A wiring system connecting two distribution boards.
A qualification awarding body.
A fault where electricity is no longer flowing through the circuit as intended but is flowing to earth via potentially fatal paths e.g. water pipes, or metallic casing of electrical equipment.
The conductor which connects all protective conductors for an entire installation to the general mass of earth or a distributor’s earth.
Earth Loop Impedance (test)
A test performed to measure the entire earth fault loop path for a circuit, it is important these values are low enough for circuit protection to adequately operate.
ECA [Electrical Contractors Association]
UK’s largest and leading trade association representing electrical, electronic, installation engineering and building services companies.
ECS [Electrical Certification Scheme?]
Safety exam and qualification to prove basic competence with electrical and site safety, the electrical equivalent of the CSCS exam.
EIC [Electrical Installation Certificate]
A certificate presented to the customer upon completion of new electrical work.
emf [Electromotive Force] *See: Voltage
A source of emf can be thought of as a kind of charge pump that acts to move charge from a point of low potential through its interior to a point of high potential, it is measured in volts.
Exposed Conductive Part
Any metallic part of an electrical installation which under normal conditions is not live, but under fault conditions can become live i.e. Metal accessories such as light switches and, metallic casing of electrical equipment.
Extraneous Conductive Part
Any metallic part NOT part of an electrical installation that could conduct electricity under fault conditions i.e. Copper water pipes.
Fault of Negligible Impedance *See: Short Circuit
A circuit which comprises of at the very least; a circuit protective device, Conductors and an electrical load or socket for a load.
In electronics and electrical engineering a fuse is a type of sacrificial overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows; it is a type of circuit breaking device.
GN3 [Guidance Note 3]
A guidance note prepared by the IET giving further guidance on Inspecting & Testing than is covered in BS7671.
HRC Fuse [High Rupturing Capacity] aka HBC [High Breaking Capacity Fuse]
A heavy duty fuse used in industry, it can interrupt safely very high fault currents.
IEE [Institute of Electrical Engineers] *NB: Obsolete (Now IET)
British professional organisation of electronics, electrical, manufacturing, and Information Technology professionals, especially electrical engineers. It has no become the IET as further bodies merge with it. They write most of the British standards regarding electrical installations… etc.
IET [Institution of Engineering and Technology]
The newer British professional organisation of Engineering and Technology.
Electrical impedance, or simply impedance, describes a measure of opposition to alternating current (AC). Basically it can be thought of as resistance in AC circuits.
All fixed electrical components in a building which are used to transmit, generate or use electricity. Generally electrical equipment which is required to be plugged in, does not constitute part of an electrical installation.
Insulation Resistance (test)
A test performed to prove the integrity of the insulation of electrical conductors.
IP Code [Index of Protection]
Most equipment meant to be used in hazardous environments or outside will require an IP rating. It consists of two digits the first a measure of protection from solid objects the second a measure of protection from liquids. The higher the number the higher the degree of protection.
The removal of all sources of electricity from a circuit.
JIB [Joint Industry Board]
The JIB is the collective term for the partnership between the ECA and Unite as distinct from the administrative organisation which was created to carry out their joint decisions.
Lamp *NB: Not “Light Bulb” *See: Load
A conductor supplying electricity to a load.
Any conductor which under normal running conditions carries electricity i.e. Line & Neutral conductors.
Any piece of equipment which utilises electricity to function.
MCB [Miniature Circuit Breaker]
A miniature circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit.
MET [Main Earthing Terminal]
Usually contained within a CCU but can be housed externally, it connects all CPCs, Main Bonding and the Earthing Conductor together.
MFT [Multi-Function Tester]
An electrical testing device which can perform the majority of tests required when completing an electrical installation.
MICC aka MIMS [Mineral Insulated Metal Sheathed] (cable)
Mineral-insulated copper-clad (MICC) cable is a variety of electrical cable made from copper conductors inside a copper sheath, insulated by inorganic magnesium oxide powder. Mainly used as fire protected cabling. Also known as Pyro!
Minor Work Certificate
Electrical work which does not involve; new circuits, changing/alteration of any protective device, or work in any special location must be certificated by a Minor Works Certificate.
Any conductor carrying electricity back from a load to the distribution board.
NICEIC [National Inspection Council for Electrical Installation Contracting]
The National Inspection Council for Electrical Installation Contracting or NICEIC is an organisation which regulates the training and work of electricians in the UK, it is run as a charitable organisation.
Notifiable Work & Part P
Residential electrical work which can only be completed by a competent person registered on a Part P scheme. This is the electrical equivalent of the Gas Safe scheme.
The SI unit of electrical resistance and impedance.
OSG [On-Site Guide]
A more useful interpretation of BS7671 and quick reference guide for working installation electricians.
A fault that occurs on a generally healthy circuit, which is created by using too much equipment.
Part P (document)
It is an approved Document of the Building Regulations regarding electrical installation work in domestic dwellings, which is statutory and legally binding.
Part P (scheme)
A competent person’s scheme for electricians. Think of electrical equivalent of plumbers Corgi/Gas Safe. For electricians to do certain types of work (see: Notifiable work) they have to legally be registered with a Part P scheme.
A circuit where loads and conductors are in parallel with each other, voltage & Current behave differently depending if the circuit is parallel or in series. All mains power in the world is delivered via Parallel Circuits, this is why all circuits contain a Line and Neutral Conductor.
Phase *NB: Obsolete, See: Line (conductor)
Potential Difference *See: Voltage
Technical term for solar panel technology.
R1, R2 & Rn (circuits)
R refers to the resistance. In a circuit R1 is the resistance of the Line conductor, R2 is the resistance of the CPC, and Rn is the resistance of the Neutral conductor.
Radial (final circuit)
A final circuit which starts at the CCU and ends at the load.
RCBO [Residual Current Breaker with Overload protection]
In laymen’s terms it is the combination device of an RCD & MCB into one single module.
RCD [Residual Current Device]
A device which breaks an electrical circuit if there is any imbalance between the line conductor current and the neutral conductor current. RCDs are used for additional protection and are great at reducing risk of harm to people.
The electrical resistance of an object is a measure of its opposition to the passage of a steady electric current. It is measured in Ohms.
Ring (final circuit)
A ring final circuit starts and ends in the CCU i.e. a ring! Typically only sockets are wired in a ring final circuit.
RMS [Root Mean Square] (Current)
Is the DC equivalent of an AC current.
A circuit where loads and conductors are in a loop connection, voltage & Current behave differently depending if the circuit is parallel or in series. Series circuits are rarely found outside electronics.
Short Circuit (fault) *aka Fault of Negligible Impedance
A short circuit in an electrical circuit is one that allows a current to travel along a path where essentially no (or a very low) electrical impedance is encountered therefore allowing a huge current to flow.
A standard unit for measurement recognised as an international standard i.e. Metre, Second…etc.
SWA [Steel Wired Armour] (cable)
Steel Wire Armoured Cable, commonly abbreviated as SWA, is a hard-wearing cable. It is found in underground systems, power networks, external wiring and cable ducting.
A device which converts the voltage of AC system to either a higher value or lower value, known as step up or step down transformers.
Twin & Earth [T&E] (cable)
Twin and earth is a name for a type electrical cable. It comprises two insulated current carrying conductors and an uninsulated CPC with an overall flat sheathing, usually grey. Line and neutral are individually insulated, the CPC is bare. Typically used in domestic installations.
Voltage [v or Volts] *NB: aka Potential Difference
The voltage between two points is a short name for the electrical force that would drive an electric current between those points. Think of it like electrical pressure.
Ze [External Earth loop Impedance]
The measure of the earth fault path external of an installation.
Zs [Final Circuit or “System” Earth Loop Impedance]
The measure of an entire circuit’s (system) earth fault path. It is the combined figure of (Ze+R1+R2).