Reference
Electrical glossary
Plain-English definitions of the terms you will find on an EICR, a certificate or a quote, from BS 7671 to Zs.
- AFDD
- Arc fault detection device. Detects dangerous arcing in cables and disconnects the circuit.
- BS 7671
- The UK Wiring Regulations, published by the IET and BSI. The current edition is BS 7671:2018 with amendments, known as the 18th Edition.
- C1
- Classification code meaning danger present. Immediate action is required.
- C2
- Classification code meaning potentially dangerous. Urgent remedial action is required.
- C3
- Classification code meaning improvement recommended. Does not make a report unsatisfactory on its own.
- Circuit breaker (MCB)
- A device that disconnects a circuit automatically on overload or short circuit.
- Competent person scheme
- A government-authorised scheme whose members can self-certify notifiable electrical work.
- Consumer unit
- The board containing the main switch and protective devices for each circuit. Often called a fuse box or fuse board.
- Distribution board
- A board that distributes supply to circuits. In commercial premises there are often several.
- EIC
- Electrical Installation Certificate. Issued for new installations, new circuits and consumer unit changes.
- EICR
- Electrical Installation Condition Report. Reports on the condition of an existing installation.
- FI
- Further investigation required without delay. Makes a report unsatisfactory until resolved.
- Insulation resistance
- A test of the insulation between conductors, measured in megohms. Higher values are better.
- IP rating
- Ingress protection rating. Shows how well equipment resists dust and water, for example IPX4.
- Limitation
- Something the inspector could not inspect or test, recorded on the report with the reason.
- Main protective bonding
- Conductors connecting incoming metal gas and water pipes to the main earthing terminal.
- MEIWC
- Minor Electrical Installation Works Certificate. Issued for small alterations without a new circuit.
- Part P
- The part of the Building Regulations in England and Wales covering electrical safety in homes.
- PAT
- Portable appliance testing. Inspection and testing of plug-in electrical equipment.
- PFC
- Prospective fault current. The maximum current that could flow in a fault, which protective devices must be able to interrupt.
- Polarity
- Correct connection of line, neutral and earth, so switches and fuses break the line conductor.
- R1+R2
- The combined resistance of the line and protective conductors of a circuit, confirming earth continuity.
- Radial circuit
- A circuit that runs out from the consumer unit and ends at the last point.
- RCBO
- A single device combining an RCD and a circuit breaker, protecting one circuit.
- RCD
- Residual current device. Disconnects the supply if current leaks to earth, protecting against electric shock.
- Ring final circuit
- A socket circuit that starts and finishes at the consumer unit, forming a loop.
- Selective licensing
- A council scheme requiring landlords in a designated area to license all privately rented homes.
- SELV
- Separated extra-low voltage. A safe low-voltage supply used in high-risk locations such as zone 0 of a bathroom.
- SPD
- Surge protective device. Limits transient overvoltages, for example from lightning.
- Supplementary bonding
- Extra bonding between metal parts in locations such as bathrooms.
- TN-C-S (PME)
- An earthing arrangement where the supplier's neutral is also used as earth. The most common in UK homes.
- TN-S
- An earthing arrangement with a separate earth conductor from the supplier, often the cable sheath.
- TT
- An earthing arrangement where the property provides its own earth electrode, common in rural areas.
- Ze
- External earth fault loop impedance, measured at the origin of the installation.
- Zs
- Earth fault loop impedance. Must be low enough for the protective device to disconnect in time during a fault.