How to wire a garage consumer unit

Helpful video reference. We use the Learn Electrics tutorial "Wiring a Garage Consumer Unit - How To - A simple step by step guide" as the video reference here. Learn Electrics is a UK electrical education channel that covers the connections stage inside the consumer unit clearly, using step-by-step diagrams that make it easy to follow the wiring sequence. Good for understanding how circuits connect to the RCD and main switch before anyone lifts a screwdriver.

1. Plan what circuits the garage needs

Start with a list. Most garages need a socket circuit (one or two 13A sockets on a radial) and a lighting circuit. If you want an electric heater, that needs its own circuit. An EV charger needs a dedicated RCBO-protected circuit, and the charger manufacturer will specify exactly what it requires.

Keep it simple. A 6-way consumer unit handles most domestic garages without difficulty. You do not need to fill every way - leaving spare capacity is not a problem.

2. Choose a compliant metal consumer unit

Plastic consumer units are no longer compliant for new or replacement work in domestic premises. The unit must be a metal BS EN 61439-3 enclosure. In practice this means a steel consumer unit from manufacturers such as Wylex, Hager, Crabtree or similar.

For RCD protection you have two main options: a dual-RCD split board (two banks of MCBs, each covered by one 63A RCD), or a full-RCBO board where every way has its own combined MCB and RCD. The RCBO option costs more but means a fault on one circuit does not take out half the board.

Since September 2022, all new consumer unit installations require a Type 2 surge protection device (SPD) under BS 7671 18th edition Amendment 2. Check whether the board you buy includes a built-in SPD or whether you need to add one separately.

3. Terminate the armoured cable and earth

If the supply from the house comes via SWA (steel wire armoured) cable, the armour must be properly terminated. Strip back the outer sheath, fan out the steel wires, and twist them into a braid before fitting a brass SWA gland. The armour connects to the earth bar in the consumer unit as a protective conductor.

For TN-C-S (PME) earthed supplies, the garage earth and neutral are tied together at the origin, so the earthing system carries through correctly. For TT earthing systems (common in rural areas), the garage will need its own earth electrode - typically a 1.2m copper earth rod driven into the ground - and all circuits need RCD protection, which they get from the consumer unit anyway.

Bring the phase (brown), neutral (blue) and earth (green and yellow) through the gland into the enclosure. The phase and neutral feed the main switch input; the earth connects to the earth bar.

4. Connect the main switch

The main switch is typically a 63A two-pole isolator (or the main switch on a dual-RCD board). The incoming phase goes to the line input terminal and the neutral to the neutral input. Torque to the manufacturer's specification - this is where the torque screwdriver earns its place.

The output of the main switch feeds the busbar on the consumer unit. On a dual-RCD board, the busbar is split into two banks, each feeding one RCD.

5. Fit and wire the MCBs

Clip the MCBs into the busbar slots. Common ratings for a garage:

• 6A Type B - lighting circuit
• 20A Type B - socket radial (up to four sockets on 2.5mm² cable)
• 32A Type B - socket radial on 4mm² cable, or a larger load
• 16A or 32A Type B - EV charger (check charger documentation)

Connect each circuit cable to its MCB. Strip the insulation to the correct length for the terminal (usually shown on the MCB body or in the data sheet). Use the torque screwdriver and tighten to the specified value. A loose terminal is a fire hazard.

All cables running to the MCBs must be rated for 70°C or above. Standard grey PVC cable (flat twin and earth or singles) is fine. Do not use 60°C-rated cable in a consumer unit.

6. Apply 30mA RCD protection to every circuit

BS 7671 Regulation 411.3.3 requires 30mA additional RCD protection for all socket circuits. In a garage, this effectively applies to everything - sockets, lighting and any fixed appliance circuits. A dual-RCD consumer unit provides this automatically if all ways are assigned to one of the two RCDs. A full-RCBO board provides individual protection per circuit.

Do not leave any circuits unprotected. An EICR will code this as C2 (potentially dangerous).

7. Label every way on the board

Before you energise anything, every MCB or RCBO must be labelled. Use the plastic label strip that comes with the board, or write clearly with a permanent marker on card behind the cover. "Sockets," "Lights," "Heater" - plain English is fine. The cover goes on last, after you have done the checks.

8. Test before energising

At minimum, carry out a visual inspection: no bare conductors, no insulation trapped under a terminal, no conductor touching another it should not. Check that all terminals are tight.

If you have test equipment (an installation tester), carry out continuity of the circuit protective conductor and insulation resistance tests on each circuit before energising. A healthy 2.5mm² socket circuit should give you an insulation resistance of well above 1 MΩ from L to E and from N to E with all switches off and appliances disconnected.

With the garage supply still isolated at the house, reconnect the SWA tails. Then go back to the house, switch on the supply to the garage, and return to check the main switch at the garage board. Switch the main switch on. MCBs should all hold. RCDs should hold. Test the RCDs using the test button on the board. Then energise each circuit one at a time.

When to call us

Garage consumer unit work is Part P notifiable in England. Richard can install and certify a compliant garage board - correct metal enclosure, SPD, RCD protection on every circuit, continuity and insulation resistance testing, and an Electrical Installation Certificate at the end. If you are getting a new supply run from the house as well, that is all done in one visit.