The short answer
A garage consumer unit (or outbuilding consumer unit) is a small distribution board installed in a detached garage, garden building, or workshop to provide safely protected electrical circuits for that outbuilding. Rather than running individual circuits directly from the main house board, the outbuilding is fed by a submain cable from the house, which connects to its own consumer unit in the garage. That board then supplies the garage's circuits — lighting, sockets, EV charger — through its own MCBs and RCDs or RCBOs. A separate board is needed because BS 7671 requires protection against earth faults and fault currents at the outbuilding, and because a separate isolation point in the garage is both a safety and a practical requirement. The installation of a garage consumer unit is notifiable Part P work in England and Wales and requires a registered electrician or building control notification.
Supplying a garage with electricity is not as simple as running a cable from the house. The wiring regulations require the outbuilding to have its own protective devices, an isolation point, and — critically — RCD protection that accounts for the longer cable runs and outdoor environment. A garage consumer unit fulfils all of these requirements.
Garage consumer unit facts
- Also calledOutbuilding consumer unit, sub-board
- Fed fromSubmain cable from main house consumer unit
- Typical contentMain isolator, RCDs/RCBOs, MCBs per circuit
- EnclosureMust be non-combustible metal (BS 7671)
- Part P statusNotifiable work — registered electrician required
- Earth protectionTN-S or TT earthing arrangement, 30 mA RCDs
Why a garage needs its own consumer unit
You might wonder why a garage with just a couple of lights and sockets needs its own board rather than having those circuits run individually from the house. There are several reasons:
- Isolation: BS 7671 requires that every installation or part of an installation has a means of isolation that can be accessed and operated safely. A garage consumer unit provides a clearly identifiable main switch in the outbuilding itself — you do not need to go back to the house to isolate the garage supply.
- Protection: any new outbuilding circuits must be fully RCD protected and have overcurrent protection appropriate to the cable. A small board in the garage allows each circuit to be individually protected.
- Earthing: garages and outbuildings present specific earthing considerations. A detached garage cannot necessarily share the house's earthing system reliably over a long cable run. An outbuilding may need its own earthing arrangement (a TT earth via a ground rod), and a garage consumer unit is the point where that earth is connected and RCD protection is provided.
- Future circuits: once a board is in place, adding an EV charger, a workshop circuit or external sockets is straightforward.
What a typical garage consumer unit contains
A garage consumer unit is usually much smaller than the main house board — a 4-way or 6-way unit is often sufficient for a domestic garage or workshop. Typical contents:
- Main switch / isolator: a double-pole switch rated for the submain supply, giving a clear isolation point in the outbuilding.
- RCDs or RCBOs: 30 mA residual-current protection on all circuits, as required by BS 7671. In a small board, a single RCD covering all circuits is often used; a larger or more complex setup may use RCBOs per circuit.
- MCBs: one per circuit, rated for the cable and load — typically a 6 A MCB for lighting, 20 A or 32 A for socket circuits, 32–50 A for an EV charger circuit.
Some garage boards also include space for a Type 2 SPD (surge protection device), which BS 7671 Amendment 2 requires for new boards in most domestic situations.
| Circuit | Typical MCB rating | Notes |
|---|---|---|
| Garage lighting | 6 A | Standard B6 MCB |
| Power sockets | 20 A or 32 A | Depending on cable and socket type |
| EV charger supply | 32 A or 40 A | Depends on charger spec; may need 7 kW = 32 A |
| Workshop equipment | 20 A–40 A | Depends on equipment; may need 3-phase |
Typical circuit ratings in a domestic garage consumer unit. Actual ratings depend on cable sizing and the installed design. Source: BS 7671:2018+A2:2022.
Regulatory and Part P requirements
In England and Wales, the installation of a new consumer unit or a new electrical circuit in an outbuilding is notifiable work under Part P of the Building Regulations. This means it must be carried out by a registered competent person (such as an NICEIC or NAPIT registered electrician) who self-certifies the work, or the work must be notified to and inspected by the local authority building control department.
On completion, you should receive an Electrical Installation Certificate (EIC) and a Building Regulations compliance certificate. The EIC confirms the installation was inspected and tested to the relevant standards at the time of installation. Keep these documents; they will be needed if you sell the property.
In Scotland and Northern Ireland, different but broadly equivalent notification and certification requirements apply under local building regulations.
Frequently asked questions
Do I need a separate consumer unit for my garage?
If you are installing new electrical circuits in a detached outbuilding, yes — you need a separate consumer unit (or at minimum a separate enclosure with the appropriate isolation and protection) rather than running circuits directly from the house board. This is a BS 7671 requirement and is also Part P notifiable work.
Can I wire my garage from the house consumer unit without a garage board?
Not for new work to current standards. BS 7671 requires isolation and RCD protection at the outbuilding for any new installation. An existing single-circuit cable run from an older house board (pre-RCD era) may still be in use in many homes, but it would not comply with current standards for new work and would not be installed that way today.
Does a garage consumer unit need an earth rod?
It depends on the earthing arrangement of the installation. If the submain cable includes a protective conductor (earth) that provides a reliable low-impedance earth path, the outbuilding may share the house's earthing system. If not — for example, with an older twin-and-earth cable that does not provide a reliable earth path over distance — an earth rod (TT earthing) at the outbuilding may be required. A registered electrician will assess and design the correct arrangement.
Sources & further reading
- IET — BS 7671:2018+A2:2022 (18th Edition Wiring Regulations)
- Electrical Safety First — outbuilding wiring guidance
- Planning Portal — Part P Building Regulations (England)
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.