The short answer
A garage consumer unit is a sub-distribution board — it is fed from the main house consumer unit by a dedicated circuit and then distributes power to the sockets, lighting and other circuits within the garage. Wiring it is notifiable work under Part P of the Building Regulations in England and Wales, so it must be carried out by a registered (competent-person) electrician who self-certifies the work to BS 7671 18th Edition. A garage board has important differences from the main house unit: the feed cable must be sized and protected correctly, and all socket-outlet circuits in a garage require RCD protection under BS 7671 because garages are treated as a higher-risk location.
Garages are treated as special locations in the wiring regulations because they combine electrical equipment with vehicles, fuel and damp conditions. This page explains what is involved in wiring a garage consumer unit and why the rules are specific.
Key facts
- Type of installationsub-distribution board, fed from main house unit
- Regulatory standardBS 7671 18th Edition, special location rules
- Part P statusnotifiable in England and Wales
- Socket RCD protectionrequired in garages under BS 7671
- Who must do itregistered (competent-person) electrician
What a garage consumer unit is and how it is fed
A garage consumer unit (also called a garage sub-board or outbuilding board) is a secondary distribution board that receives its supply from a dedicated circuit in the main house consumer unit. It is not connected directly to the meter or the incoming mains — the main house board is its source. This circuit from the house to the garage is protected at the main board by an MCB (or RCBO) rated to match the cable size, and that cable — usually SWA (steel wire armoured) if buried or running externally, or suitable twin-and-earth if routed internally — must be sized for the expected load and run length.
At the garage end, the sub-board receives the supply into its own main isolating switch and distributes it to the circuits within the garage. The sub-board provides local isolation: you can switch off all power to the garage without going back to the house board.
RCD protection and BS 7671's garage rules
Garages fall within the scope of BS 7671's provisions for locations containing a bath or shower and are also treated as higher-risk locations in their own right because they frequently contain vehicles, petroleum spirit, power tools and damp or wet conditions. The key requirement that differs from ordinary domestic circuits is:
- All socket-outlet circuits in a garage require RCD protection — this is a specific requirement under BS 7671 and applies regardless of whether the socket is a standard 13 A outlet or a dedicated outlet for a specific appliance.
- Lighting circuits in a garage should also have RCD protection as good practice, and this is the typical approach when a new sub-board is fitted.
- EV charger circuits: if a dedicated EV charging point is being installed in the garage, additional requirements apply — in particular, the circuit may need a Type A or Type B RCD depending on the charger type (domestic EVSE often requires at minimum a Type A device). A registered electrician will specify the correct protective device for the charger being installed.
A modern garage sub-board is typically an RCBO board (one RCBO per circuit) or a board with a single RCD covering all circuits. The RCBO arrangement is generally preferred because a fault on one circuit — say a socket tripping due to a damp power tool — isolates only that circuit and leaves the lighting and other circuits live.
| Circuit type | RCD requirement | Notes |
|---|---|---|
| Socket outlets in garage | Required — BS 7671 | Applies to all socket-outlet circuits |
| Lighting in garage | Required as good practice | Typical on a modern sub-board |
| EV charger circuit | Type A or B RCD depending on charger | Confirm with electrician for specific EVSE |
| Feed from house to garage | Protected at main board MCB/RCBO | Cable size must match protection rating |
General guidance based on BS 7671 18th Edition requirements. A registered electrician confirms the specific requirements for your installation.
Earthing arrangements for a detached garage
The earthing arrangement for a garage sub-board depends on whether the garage is attached to or detached from the house, and on the supply method used. The key considerations under BS 7671 are:
- Attached garage: if the garage is physically connected to the house (sharing a wall), the earthing can normally extend from the house installation via the supply cable. The earth conductor in the supply cable bonds the garage sub-board to the house's earthing system.
- Detached garage: a detached building presents a more complex situation. BS 7671 requires that circuits supplying equipment in a separate building must have an earth connection, but simply relying on the earth conductor in a long cable from the house can be inadequate, particularly for TT supplies. An additional earth electrode at the detached building is often required, and a registered electrician will determine the correct earthing system based on the supply type and installation.
- No separate neutral-earth link: a sub-board should never have its own separate neutral-to-earth link (that would create a TN-S / TT hybrid arrangement with serious consequences). The earthing and neutral connections at a sub-board are handled differently from those at the main board.
These earthing details are technical and site-specific. They are among the reasons a garage consumer unit installation is work for a registered electrician rather than a general handyperson.
Why this is notifiable and what certification you receive
Installing a garage consumer unit is notifiable work under Part P of the Building Regulations in England and Wales. Notifiable work must be:
- carried out by a registered electrician under a government-authorised competent-person scheme (NICEIC, NAPIT, ELECSA, STROMA or similar), who self-certifies the work; or
- notified to local-authority building control before work starts, with inspection after completion.
On completion you should receive an Electrical Installation Certificate (EIC) recording the technical details and test results, and a Building Regulations compliance certificate confirming Part P notification. Both are required. If you have an existing EIC for your house installation, the garage installation is a separate notifiable job that requires its own EIC. Keep both with your property documents.
Frequently asked questions
Do I need Part P certification for a garage consumer unit?
Yes. Installing a garage consumer unit is notifiable work under Part P of the Building Regulations in England and Wales. It must be carried out by a registered (competent-person) electrician who self-certifies it, or notified to building control. You should receive an Electrical Installation Certificate and a Building Regulations compliance certificate on completion.
Does a garage need its own consumer unit?
Not always — a small garage with one or two circuits could be served by a dedicated spur from the house board without a separate sub-board. However, once a garage has several circuits (sockets, lighting, EV charger), a dedicated sub-board provides local isolation and is the neater, safer arrangement. A registered electrician will advise based on your garage layout and intended use.
Does a garage consumer unit need to be metal?
Yes. Since the 18th Edition of BS 7671 came into force, consumer units in domestic premises must have a non-combustible (typically metal) enclosure. This applies to garage sub-boards as well as main house boards.
Sources & further reading
- Electrical Safety First — replacing a consumer unit (best practice guide)
- IET — BS 7671 18th Edition wiring regulations overview
- NICEIC — what is Part P and who needs to register?
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.