Garage Electrics: Wiring, Sockets, and Lighting Guide

Whether it is a detached garage used as a workshop, an integral garage converted to a utility space, or a double garage with an EV charger, the electrical installation must be designed, installed, and certified to comply with BS 7671:2018+A4:2026 and notified under Part P of the Building Regulations.

A garage electrical installation typically involves supplying power from the house via an underground SWA (Steel Wire Armoured) cable, installing a sub-distribution board in the garage, and wiring individual circuits for sockets, lighting, and any specialist equipment. The environment inside a garage — unheated, potentially damp, subject to dust and mechanical damage — places specific requirements on the IP ratings of accessories and the cable installation methods used.

This guide covers everything from SWA cable selection and burial depth through to EV charger preparation and the certification requirements on completion.

The standard method of supplying a detached garage is an SWA (Steel Wire Armoured) cable run underground from the house consumer unit to a sub-distribution board in the garage. SWA cable is designed for direct burial — the steel wire armour provides mechanical protection and also serves as the circuit protective conductor (CPC) for the earth path.

The cable sizing must account for the installation method (direct burial), the soil thermal resistivity, and the voltage drop over the full cable run. For a typical 10 to 15 metre run supplying a light workshop load, 4.0mm 3-core SWA is usually sufficient. For runs exceeding 20 metres or loads including an EV charger, upsize to 6.0mm or 10.0mm.

A sub-distribution board (often called a garage consumer unit) is installed in the garage to distribute power to the individual circuits. This is preferable to running individual cables from the main house board for several reasons:

The sub-distribution board should be a metal enclosure (as required by Amendment 4 of BS 7671 for domestic premises). It should be mounted at a height that is accessible but protected from accidental damage — typically 1.2m to 1.8m above floor level. The incoming SWA cable should enter via a properly fitted SWA gland, and the board should include a main switch or isolator for the incoming supply.

The main switch in the garage board acts as the means of isolation for the garage installation. It must be readily accessible and clearly labelled. If the garage is used by multiple people (for example, a shared workshop), consider a lockable isolator for additional safety.

The IP (Ingress Protection) rating of electrical accessories must match the environmental conditions in the garage. BS 7671 requires the electrician to assess the external influences at the installation location and select accessories with the appropriate protection.

Lighting in a garage should be robust and appropriately rated. LED batten lights with IP65 rating are a popular choice — they provide excellent illumination, are resistant to moisture and dust, and are energy-efficient. For a workshop area, consider higher lumen output fittings positioned to minimise shadows on the workbench.

All socket outlets rated up to 32A and all lighting circuits in a garage must be protected by a 30mA RCD in accordance with BS 7671 Regulation 411.3.3. This requirement applies regardless of whether the garage is integral or detached.

Using RCBOs (combined MCB and RCD in one device) in the garage sub-board is the best practice approach. Each circuit gets its own RCD protection, so a fault on one circuit does not trip the protection on another. This avoids the common complaint of "the garage RCD keeps tripping and I lose all power."

The number and position of sockets and lights depends on how the garage will be used. A basic single garage used for car parking and light storage needs fewer outlets than a double garage workshop. Plan the layout with the homeowner before installation.

Cable routing in a garage is typically surface-mounted in PVC mini-trunking or conduit, clipped directly to the wall surface, or run in the roof void above the ceiling. Surface mounting is practical and allows easy future modification. Ensure cables are routed in safe zones (horizontal and vertical from accessories) or protected by RCD where they are not in safe zones.

Even if the homeowner does not currently own an electric vehicle, preparing the garage electrical installation for a future EV charger is sensible and adds value to the property. The cost of adding a spare way and running a cable during the initial installation is minimal compared to retrofitting later.

For full details on EV charger installation requirements, see the EV Charger Installation Guide. The key point for garage installations is to plan the capacity and cable routes at the design stage, not as an afterthought.

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All new garage electrical work must be tested in accordance with BS 7671 Chapter 6 (Initial Verification) and certified with an Electrical Installation Certificate (EIC). The tests are the same as for any new domestic circuit:

The Electrical Installation Certificate must cover all new circuits including the SWA cable supply. If you are registered with a competent person scheme, the EIC is used to self-certify the work and notify building control. The homeowner should receive a copy of the EIC and the schedule of test results for their records.

Garage electrical installations are bread-and-butter work for domestic electricians. They are relatively straightforward, have good margins (particularly on the SWA cable and trenching), and often lead to follow-on work such as EV charger installation, workshop fit-outs, or additional outbuilding supplies.

The key to profitability is accurate quoting on the first visit and efficient on-site delivery. Here is how Elec-Mate helps:

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