Last updated 7 October 2026
Quick answer: this glossary explains, in plain English, the words you will meet on an electrician’s quote, a certificate or an EICR, grouped by where you meet them: the consumer unit, the wiring, the measurements, the paperwork, and the Scottish rules. It uses UK terms, and where Scotland differs from England and Wales (building warrants, the Repairing Standard, Part P) it says so.
For what the codes on a report mean, and which faults usually earn each one, see our companion page: common electrical fault codes and their meanings.
Your consumer unit and the devices in it
| Term | Plain English meaning |
|---|---|
| Consumer unit (fuse box) | The box that splits your supply into circuits and holds the devices that protect each one. The Scottish Government’s landlord guidance notes that it is known by some as a fuse box. |
| Main switch | Turns off everything the consumer unit feeds. It is the first thing to switch off before anyone works on the installation. |
| MCB (miniature circuit breaker) | A resettable switch that turns a circuit off when too much current flows, from an overload or a short circuit. Markings such as B32 give its tripping type (B) and rating in amps (32). |
| RCD (residual current device) | A device that switches off automatically when it detects current leaking to earth. RCDs give a high level of protection against electric shock and reduce the risk of fire from faulty equipment. Scottish landlord guidance requires at least one rated at no more than 30 mA in the main consumer unit of a let home. |
| RCBO | An MCB and an RCD in one device, protecting a single circuit. If one circuit has a fault, only that circuit goes off. |
| Split load board | A consumer unit where one or two RCDs each protect a group of circuits. It remains a compliant arrangement; a single leak simply switches off the whole group. |
| AFDD (arc fault detection device) | Detects dangerous arcing in wiring or flexes and switches off. Under BS 7671 it is required on certain socket circuits in HMOs, high rise residential buildings, purpose built student accommodation and care homes, and recommended rather than required in an ordinary house. |
| SPD (surge protection device) | Diverts voltage spikes, for example from lightning, away from your wiring and electronics. Many have a status window showing whether they still work. In a single home the owner can decline one, and that decision is recorded. |
| Rewireable fuse | The old style fuse carrier with a length of fuse wire. Not a fault in itself if it still protects the circuit properly, but fuse wire of the wrong (oversized) rating is a C2 on an EICR. |
| Plug fuse | The fuse inside a UK plug, usually 3 A or 13 A, which protects the appliance and its flex. Replace it only with one of the same rating. |
| Blank | A cover that fills an empty space in the consumer unit. A missing blank that leaves live parts open to touch is a C1. |
Thinking of changing the board itself? Our page on consumer unit upgrades in Aberdeen covers board types, prices and what the certificate should show.
Supply, earthing and wiring
| Term | Plain English meaning |
|---|---|
| Cutout and meter | The sealed fuse unit where the supply cable enters your home (also called the service head), and the meter beside it. They belong to the network operator or your energy supplier, not to you. Report problems with them by calling 105. |
| Network operator (DNO) | The company that owns the cables and substations bringing electricity to your street. Calling 105 is free and puts you through to your local one, which handles power cuts. |
| Meter tails | The short, thick cables from the meter to the consumer unit. They form part of your installation. |
| PME (TN-C-S) | A common supply earthing arrangement, where the network uses one combined conductor for neutral and earth. It matters most for outdoor EV chargers, which need protection if that conductor breaks. |
| Earthing | A protective path that carries fault current safely to earth, so that a fuse, circuit breaker or RCD switches off the faulty circuit before anyone gets a shock. |
| Main protective bonding | Earth cables connecting incoming metal water, gas and oil pipes to the main earthing terminal. It reduces the voltage that could appear between metal parts during a fault. Missing bonding is a C2. |
| Supplementary bonding | Extra bonding connections, usually in a bathroom, between metal parts that could be touched at the same time. BS 7671 allows it to be left out only where every condition it sets is met. |
| Line, neutral and earth | The three conductors in most circuits. Line (often called live) carries the supply, neutral completes the circuit, and earth is the safety path. In modern UK wiring they are brown, blue, and green and yellow. Older installations used red and black, which is not a fault on its own. |
| Circuit | One cable route fed from its own protective device: for example the upstairs lights, the kitchen sockets or the cooker. |
| Ring final circuit | The usual UK socket circuit: a cable loop that leaves the consumer unit, passes every socket and comes back. A break in the loop is a C2 on an EICR. |
| Radial circuit | A circuit that runs out from the consumer unit and ends at the last point, used for lighting, cookers, showers, EV chargers and many socket circuits. |
| Borrowed neutral | Two circuits sharing one neutral, often found between upstairs and downstairs lighting. It means switching off one breaker may not make a circuit safe, and it is a C2. |
| Three phase | A supply with three line conductors, common in commercial premises and needed for 22 kW EV charging. Most homes have a single phase supply. See our three phase electrical work page. |
| IP rating | Two digits showing how well a fitting keeps out solids (first digit) and water (second digit). Outdoor and bathroom fittings need a rating suited to where they are. |
Measurements you will see on quotes and reports
| Term | Plain English meaning |
|---|---|
| Volt (V) | Electrical pressure. UK homes are supplied at a nominal 230 V. |
| Amp (A) | How much current flows. Breakers, fuses and cables are rated in amps. |
| Watt (W) and kilowatt (kW) | The rate at which an appliance uses power. Watts divided by volts gives amps: a 2,300 W kettle on 230 V draws about 10 A. |
| Kilowatt hour (kWh) | The unit on your bill: 1 kW used for one hour. A 3 kW heater on for two hours uses 6 kWh. |
| mA (milliamp) | A thousandth of an amp. An RCD’s 30 mA rating is the leakage at which it trips. |
| Insulation resistance | A test of how well the insulation keeps current where it should be. A reading below 1 MΩ (one megohm) fails the BS 7671 limit. |
| Earth fault loop impedance (Zs) | A test result showing whether a fault would draw enough current to trip the protective device quickly enough. Too high a value, with no RCD on the circuit, is a C2. |
| Polarity | Whether line and neutral are connected the right way round. Wrong polarity at the origin of the installation is a C1. |
Inspections, certificates and codes
| Term | Plain English meaning |
|---|---|
| BS 7671 | The UK wiring regulations, also called the IET Wiring Regulations or the 18th Edition. The current version is BS 7671:2018+A4:2026, published on 15 April 2026; the previous edition was withdrawn on 15 October 2026. |
| EICR (Electrical Installation Condition Report) | An inspection and test of an existing installation, ending with an overall result of satisfactory or unsatisfactory. Older documents call it a Periodic Inspection Report (PIR). |
| C1, C2, C3 and FI | The classification codes on an EICR. Only C1 (danger present) and C2 (potentially dangerous) make a report unsatisfactory. C3 (improvement recommended) and FI (further investigation is advised) are advisory. |
| Limitations | Parts of the installation the inspector agreed not to inspect or could not reach, recorded in the report with the reason. |
| EIC (Electrical Installation Certificate) | The certificate for new work: a new installation, a rewire, a new circuit or a new consumer unit. |
| Minor Works Certificate | The certificate for an addition or alteration that does not include a new circuit, such as an extra socket on an existing circuit. Scottish landlord guidance recommends recording EICR remedial work on one. |
| PAT (in service inspection and testing of electrical equipment) | Checks on portable appliances such as kettles, fridges and heaters. Scottish landlords must have it done on appliances they provide, alongside the EICR. |
| Skilled person (electrically) | BS 7671’s term for someone with the education, training and practical skills to see and avoid the risks electricity creates. In Scotland an EICR on a let home must be completed by one. |
| NICEIC and NAPIT | Certification bodies that assess electrical businesses against BS 7671 and their own rules, and publish registers you can search. A NICEIC Approved Contractor is a business, not an individual. |
| Approved Electrician | In Scotland, the senior grade of individual electrician set by the Scottish Joint Industry Board, shown on the person’s ECS card. |
For which certificate you should get after which job, see the UK electrical certificate types explained.
Scottish rules and terms
| Term | Plain English meaning |
|---|---|
| Repairing Standard | The legal standard every private let home in Scotland must meet, set by section 13 of the Housing (Scotland) Act 2006. It includes electrical installations, including RCDs, being in a reasonable state of repair and in proper working order. |
| Annex D3 | The part of the Scottish Government’s statutory guidance for private landlords that covers electrical safety: an EICR and appliance testing before a first let and at least every five years, at least one 30 mA RCD in the main consumer unit, and C1 and C2 items put right. |
| Tolerable Standard | The basic standard every Scottish home must meet, whether owned or rented. Under section 86 of the Housing (Scotland) Act 1987, a home with an electricity supply must have an electrical installation that is adequate and safe to use. |
| Building warrant | Permission from the local council’s building standards service, needed before some work starts. Rewiring a house of up to two storeys does not need one; rewiring a flat or maisonette does. The owner who orders the work holds the duty to get it. Aberdeen City Council covers the city; Aberdeenshire Council covers towns such as Peterhead, Ellon and Westhill. |
| Certificate of Construction | A certificate issued by an approved certifier of construction to confirm that work covered by a warrant meets the building regulations. NICEIC says contractors on its Certifier of Construction scheme can speed up the warrant process. |
| Part P | Part of the building regulations for England and Wales. It has never applied in Scotland, so a quote for a Scottish home that mentions Part P sign off was written for the wrong country. |
| Building Control | The English and Welsh term. Scotland has building standards and building warrants instead. |
EV charging and newer technology
| Term | Plain English meaning |
|---|---|
| Smart charger | An EV charger that can schedule charging, defaults to off peak charging and adds a randomised start delay. Every new home charger in Great Britain has had to be smart since 30 June 2022. |
| RDC-DD | A device that detects 6 mA of DC fault current on an EV charging circuit. If the charger has one built in, a Type A RCD on its supply is acceptable; otherwise a Type B RCD is needed. |
| Open PEN protection | Protection for an outdoor charger on a PME supply in case the combined neutral and earth conductor breaks. |
| Load management | A charger feature that reduces charging current when the rest of the house is using a lot of power, so the main fuse is not overloaded. |
| Rewire | Replacing all of the fixed wiring, usually with a new consumer unit, ending with an EIC. See rewiring in Aberdeen for what a rewire involves and costs. |
Frequently asked questions
Is a fuse box the same as a consumer unit?
Yes, in everyday use. “Consumer unit” is the proper name; “fuse box” comes from older boards that used fuses rather than circuit breakers.
What is the difference between an RCD and an RCBO?
An RCD detects current leaking to earth and often protects a group of circuits. An RCBO combines that with overcurrent protection for one circuit, so a fault switches off only that circuit.
What is the difference between an EIC and an EICR?
An EIC certifies new work, such as a new circuit, consumer unit or rewire. An EICR reports on the condition of an existing installation.
Does Part P apply in Scotland?
No. Part P belongs to the building regulations for England and Wales. In Scotland some electrical work needs a building warrant from the local council instead.
What does the Repairing Standard mean for the electrics in a rented home?
The installation, including RCD protection, must be in a reasonable state of repair and proper working order. In practice that means an EICR and appliance testing at least every five years, and any C1 or C2 put right.
What does “skilled person” mean on an EICR?
A person with the education, training and practical skills to recognise and avoid electrical risks. Scottish landlord guidance accepts members of recognised registration schemes, or someone who can meet its competence checklist.
Seen a term on a quote or report that is not here? Call 07304 027013 (Monday to Friday 8am to 6pm, Saturday 9am to 1pm) or send us your question and we will explain it.
