The short answer
A consumer unit is the distribution board that receives the incoming electricity supply to your home and divides it into separate circuits — lighting, sockets, cooker, shower, and so on — each with its own protective device. The term is defined in BS 7671 (the IET Wiring Regulations, 18th Edition) as a particular type of distribution board that contains a main switch and protective devices for each circuit. Inside a modern consumer unit you will typically find MCBs (miniature circuit breakers), one or more RCDs (residual current devices) or RCBOs (combined devices), and increasingly a surge protection device (SPD). The older everyday term for the same panel is 'fuse box' or 'fuse board', although those names originally referred to boards fitted with rewireable fuses rather than resettable breakers.
Most UK homes have exactly one consumer unit. It is the central point of the electrical installation — the place where power comes in, is divided up, and is protected. Understanding what is inside it helps you make sense of why it trips, what it protects against, and when it might need replacing.
Key facts
- Technical termBS 7671 / IET Wiring Regulations
- Also calledfuse box, fuse board, fuseboard
- Main switchisolates the whole installation
- Protective devicesMCBs, RCDs, RCBOs
- Current standard18th Edition BS 7671 (2018, amd. 2022)
What a consumer unit contains
Strip away the plastic or metal enclosure and a modern consumer unit typically holds three types of component:
- Main isolator switch: a double-pole switch that disconnects both the live and neutral conductors and cuts power to the whole board. On a modern unit it is usually rated at 100 A. Turning it off makes the board safe to work on — though the incoming tails from the meter remain live.
- RCD or RCBOs: a residual current device monitors a group of circuits (or, in the case of an RCBO, a single circuit) for any imbalance between the live and neutral currents — the signature of current leaking to earth, typically through a person or a fault. It disconnects within milliseconds, which is fast enough to prevent a lethal shock in most circumstances. BS 7671 18th Edition requires RCD protection for most circuits in a domestic installation.
- MCBs (miniature circuit breakers): one per circuit, rated for the current that circuit is designed to carry (commonly 6 A for lighting, 32 A for a ring final, 40 A or 45 A for a cooker). An MCB trips automatically on overload or short circuit and can be reset by hand once the fault is cleared.
Some boards also contain a surge protection device (SPD), which is required on new or replacement boards in most domestic installations under the 18th Edition (Amendment 2). An SPD clamps transient voltage spikes — from lightning or switching on the supply network — before they can damage sensitive electronics.
| Component | What it does | Typical rating |
|---|---|---|
| Main switch / isolator | Disconnects whole board | 100 A (typical domestic) |
| MCB | Trips on overload / short circuit | 6 A, 16 A, 20 A, 32 A, 40 A, 45 A, 50 A |
| RCD | Disconnects on earth leakage | 63 A / 80 A, 30 mA sensitivity |
| RCBO | MCB + RCD in one device | Per circuit, 30 mA sensitivity |
| SPD | Clamps voltage spikes | Required on new boards (18th Ed amd 2) |
Typical components in a domestic consumer unit. Ratings are indicative; actual values depend on the installation design. Source: BS 7671:2018+A2:2022.
Consumer unit versus old fuse box: what changed
The phrase 'fuse box' dates from the era of rewireable fuses — ceramic carriers with a strand of fuse wire that would melt if the circuit was overloaded. Those boards protected wiring from fire but offered no residual-current protection: they could not detect a slow current leaking to earth through a person or a damaged cable.
The modern consumer unit replaced rewireable fuses with resettable MCBs and added RCDs, transforming the protection level. The change from plastic enclosures to non-combustible metal enclosures came with an amendment to the 18th Edition of BS 7671 in 2016 (Regulation 421.1.201), which requires that domestic consumer units be enclosed in non-combustible material — the reason virtually all boards sold since then have a metal case. Older plastic-cased boards did not break any rule in force when they were installed, but they cannot be used for new or replacement work.
Where the consumer unit sits in your electrical installation
Electricity arrives at your home via the service cable, goes through the DNO (distribution network operator) sealed cut-out fuse, then through your meter, and finally reaches the consumer unit via the meter tails. Those tails are the only conductors in the installation you cannot isolate yourself — they remain live even with the consumer unit's main switch off, because they sit on the supplier's side of the metering.
From the consumer unit, each circuit runs out through its own final circuit cables to sockets, light fittings, fixed appliances and so on. The number of circuits, and therefore the number of 'ways' or slots in the board, depends on the size and age of the property. A typical modern home might have a 10-way or 12-way unit; a larger property or one with many separate circuits may need 16 or more ways.
Frequently asked questions
Is a consumer unit the same as a fuse box?
Yes, in everyday use the terms are interchangeable. 'Consumer unit' is the technical term used in BS 7671 and by electricians; 'fuse box' and 'fuse board' are older everyday names for the same panel. The main practical difference is what is inside: a modern consumer unit uses resettable circuit breakers and RCDs, while an old fuse box may use rewireable fuse wire with no residual-current protection.
Why does my consumer unit need to be metal?
A regulation in BS 7671 18th Edition (Regulation 421.1.201) requires that domestic consumer units be enclosed in non-combustible material — typically steel. The change followed concern that the arc energy from a fault inside a plastic-cased board could ignite the enclosure. All consumer units sold for new or replacement work since around 2016 must meet this requirement.
How many circuits does a consumer unit have?
It depends on the size of the property and how the installation is laid out. A typical modest home might have 8–12 circuits; a larger house with separate lighting and socket circuits for each floor, plus circuits for a cooker, shower, EV charger and outbuilding, could need 16 or more. The number of slots in the board is described as its 'ways'.
Sources & further reading
- IET — BS 7671:2018+A2:2022 (18th Edition Wiring Regulations)
- Electrical Safety First — replacing a consumer unit best practice guide
- NICEIC — consumer unit guidance
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property and installation. They are guidance, not a quotation.