How to Wire a Garage Consumer Unit: A Practical Guide for UK Electricians

A dedicated garage consumer unit provides local isolation and circuit protection for electrical equipment installed in a garage, workshop, shed or other outbuilding. A typical installation may supply garage lighting, general-purpose socket outlets, power tools and workshop equipment, an electric garage door, heating or ventilation, external lighting, security systems, and future equipment such as an EV charge point.

Although many people search for how to wire a garage consumer unit, this is not normally an appropriate DIY project. Installing a new consumer unit or circuit involves electrical design, safe isolation, earthing arrangements, protective-device selection, inspection, testing and certification, and should be completed by a suitably competent electrician in accordance with the current edition of BS 7671 and any applicable Building Regulations.

Quick answer: how to wire a garage consumer unit

In short: assess the intended load and the existing supply, confirm the correct earthing arrangement for the property, design and route a suitably sized submain cable to the garage, fit a compatible metal consumer unit with the right RCD/RCBO protection and a backup overcurrent device, wire the final circuits (lighting, sockets, and any fixed equipment), then inspect, test, certify and notify the completed work. The full process, including the earthing decision and cable design that most guides skip over, is set out step by step below.

On this page

• What is a garage consumer unit?

• Does every garage need its own consumer unit?

• How to wire a garage consumer unit: the professional process

• Garage consumer unit kits: Wylex and Crabtree

• How much does it cost to replace a garage consumer unit?

• Common mistakes to avoid

• FAQs

What is a garage consumer unit?

A garage consumer unit is a small distribution board that controls and protects the final circuits within a garage or outbuilding. It is normally supplied by a dedicated submain originating from the property's main consumer unit or another suitable distribution point, and divides that incoming supply into separate circuits, for example a lighting circuit, a socket-outlet circuit, a dedicated circuit for fixed machinery, an outdoor lighting circuit, or a garage-door circuit.

The consumer unit usually incorporates a main switch or other suitable incoming device, along with MCBs, RCBOs or other protective devices selected for the installation. Modern consumer units intended for domestic use should be selected and assembled as a complete manufacturer-approved system, mixing protective devices from different product ranges can invalidate the assembly's testing and the manufacturer's instructions. Electrium, for example, specifies that only compatible Wylex or Crabtree devices should be fitted within their respective consumer-unit systems, and Crabtree's own installation instructions state that Starbreaker busbars, MCBs, RCCBs, RCBOs, AFDDs and main switches must be used within Starbreaker units.

Does every garage need its own consumer unit?

Not necessarily. The appropriate arrangement depends on whether the garage is attached or detached, the number of circuits required, anticipated maximum demand, distance from the main building, installation method, environmental conditions, earthing and bonding requirements, and whether future loads are likely to be added.

A small attached garage with one light and one socket may sometimes be served from appropriately designed existing circuits. A detached garage with several socket outlets, lighting, workshop equipment or significant future loads will often benefit from a dedicated submain and local consumer unit, giving better circuit separation, convenient isolation, and scope for future expansion. The decision should be based on an electrical design, not simply the number of accessories being installed.

BS 7671 treats the cable feeding a detached garage as a distribution circuit in its own right, meaning the supply itself, not just the final circuits inside the garage, must meet its own earth fault loop impedance (Zs) and disconnection time requirements under Section 411.

How to wire a garage consumer unit: the professional process

A compliant garage consumer unit installation should begin with design and assessment, not with choosing a cable size or copying a generic wiring diagram.

1. Assess the intended garage loads

Establish how the garage will actually be used. A garage used only for storage and occasional lighting has very different requirements from a workshop containing welders, compressors, bench tools, electric heaters, vehicle lifts, commercial machinery or EV charging equipment. Consider both the present load and any reasonably foreseeable additions, how many socket outlets, whether high-powered tools or continuous loads are expected, whether three-phase equipment is anticipated, and whether an EV charger, battery or solar installation could be added later.

The total of the circuit-breaker ratings does not, by itself, establish maximum demand. Appropriate diversity and the actual operating characteristics of the loads must be considered.

2. Check the existing installation and supply capacity

Before adding a garage supply, assess the condition and capacity of the existing installation: the distributor's service-head rating, meter tails and main switch rating, existing consumer unit capacity, earthing arrangement, main protective bonding, existing demand, available ways in the main consumer unit, prospective fault current, earth fault loop impedance, and the condition of any circuit already feeding the garage.

Where the existing wiring is old, damaged or undocumented, further investigation or an Electrical Installation Condition Report may be advisable before alteration. A garage consumer unit should never simply be connected to an existing circuit without confirming the upstream equipment and conductors are suitable.

3. Determine the earthing arrangement

The earthing arrangement is one of the most important aspects of supplying a detached garage. The designer must establish whether the property uses TN-S, TN-C-S (commonly associated with PME), TT, or another permitted arrangement, and then decide whether the property's earthing will be extended to the garage or whether a separate arrangement is appropriate.

Relevant factors include extraneous-conductive-parts within the garage, metallic water or gas services, structural steelwork, simultaneously accessible conductive parts, the risk associated with a broken PEN conductor, equipment installed outside the garage, EV charging equipment, and the practicality of protective bonding. There is no universal rule that every detached garage must have its own earth electrode, nor should the house earth automatically be exported without assessment, the arrangement must be designed for the specific installation.

For a fuller walk-through of this decision and its bonding implications, see Voltimum's guidance on installing an electrical supply to an outbuilding and on determining an extraneous-conductive-part.

4. Design the garage submain

The cable and protective device should be selected using calculations that consider design current, protective-device rating, cable current-carrying capacity, installation method, grouping, thermal insulation, ambient temperature, voltage drop, earth fault loop impedance, prospective fault current, required disconnection time, mechanical protection, length of run and future demand.

Steel wire armoured (SWA) cable is frequently selected for detached garages because it offers mechanical protection and suits many outdoor or buried installations when correctly specified. It is not automatically the right answer in every case, though, other cable types or wiring systems may suit the route and environmental conditions better. Generic statements such as "use 6mm² cable for a garage" are unsafe; the correct conductor size can only be determined from the actual design conditions.

5. Plan the cable route

Agree the submain route before work begins, buried underground, fixed externally to a building, run through suitable ducting, overhead on a properly designed support system, or routed internally to an attached garage. For buried cables, consider expected ground disturbance, mechanical protection, route identification, suitable depth for the site conditions, drainage and water ingress, duct size and pulling access, separation from other services, and termination arrangements at each end. Document the route so future occupants and contractors can identify where the cable runs.

Regulation 522.8.10 requires buried cables to have adequate mechanical protection or be installed at a depth unlikely to be disturbed, without specifying a figure for this application (the specific 600mm depths named elsewhere in BS 7671 apply to particular special locations, such as agricultural premises or caravan parks, not general domestic garage supplies). In practice, most installers treat 600mm as established good practice for a domestic SWA run, adding conduit or cable-cover tiles where that depth can't be achieved. Where the cable enters the building, terminate the armour properly, strip back the outer sheath, fan out and twist the armour wires into a tail, and fit a proper brass SWA gland rather than relying on the gland alone for earth continuity.

6. Select the garage consumer unit

The board should provide enough usable ways for the initial installation and reasonable future expansion, a small garage may need circuits for lighting, socket outlets, external lighting or a garage door, and a spare or dedicated equipment circuit. A board with spare capacity is usually preferable to the smallest possible enclosure.

Selection considerations include the number of final circuits, main-switch rating, RCBO or RCCB configuration, surge protection, AFDD requirements or recommendations, available spare ways, IP rating, impact resistance, corrosion risk, ambient temperature, indoor or outdoor mounting, and compatibility with the manufacturer's protective devices. Distribution boards intended to be operated by ordinary persons should conform to the applicable BS EN 61439 series requirements, and the IET highlights the need to consider environmental and mechanical-impact protection where consumer units are mounted externally.

7. Choose between MCBs, RCCBs and RCBOs

Main switch with individual RCBOs: an all-RCBO arrangement gives each circuit its own combined residual-current and overcurrent protection: better circuit separation, reduced inconvenience when one circuit develops a fault, easier fault finding, and less risk of a single fault disconnecting all garage circuits. For many garage and workshop installations, this can be preferable to placing several circuits behind one shared RCCB.

RCCB with MCBs: a smaller garage board may use a single RCCB to provide residual-current protection across several MCB-protected circuits. This can be cost-effective, but a residual-current fault on one circuit will disconnect every circuit sharing that RCCB, in a garage, that could mean losing lighting and socket power at the same time. Weigh the consequences of unwanted tripping before choosing this route.

RCD type: the RCD type must be selected according to the connected equipment and the possible presence of DC components or non-sinusoidal residual currents. The IET notes that Type AC RCDs should only serve fixed equipment where it is known that the load current contains no DC components. Modern garage loads, electronic power supplies, variable-speed tools, LED drivers, chargers and control equipment, increasingly do introduce these, so assess whether Type A or another RCD type is genuinely required rather than defaulting to whatever the cheapest board ships with.

8. Consider surge protection

A surge protective device (SPD) can reduce the risk of damage from transient overvoltages. Since Amendment 2 to the 18th Edition (September 2022), new consumer unit installations generally require Type 2 SPD protection. The designer should determine where the SPD is best located and ensure it is correctly coordinated with the rest of the installation, at the origin of the main installation, within the garage consumer unit, or at multiple coordinated points. Simply adding a second SPD without considering coordination, cable lengths and existing protection is not sufficient. For a full breakdown of SPD types, connection type, the 0.5m lead-length rule and backup protection, see Voltimum's guide: What is an SPD in electrical installations?

9. Consider arc fault protection

Arc Fault Detection Devices (AFDDs) are designed to detect certain hazardous arc faults that conventional circuit breakers and RCDs may not pick up. The need for AFDD protection should be assessed against the current requirements of BS 7671, the type of premises, the circuit, and the fire risk, the IET advises that the designer or installer is best placed to make this judgement, taking account of the relevant risks and installation conditions. Garages containing combustible materials, timber construction, valuable vehicles or equipment may warrant particular consideration here, and it's a factor worth raising with the client even where it isn't strictly mandated for the installation type.

10. Position, install and terminate the board

The consumer unit should be readily accessible, securely mounted, protected against impact, clear of water ingress and condensation, and away from flammable materials. A standard indoor unit shouldn't be installed outdoors or in a persistently damp position unless housed in an appropriate enclosure, Crabtree's indoor consumer-unit instructions, for example, rate certain products IP2XC for that reason. Even without direct rainwater ingress, condensation can still be an issue in an unheated garage.

Once safely isolated, mount the enclosure, install the approved devices and terminate conductors per the manufacturer's instructions, correct cable-entry protection, glands, segregation, conductor identification, blanking plates in unused ways, and no swarf or debris inside. Tighten terminals to the manufacturer's stated torque using calibrated equipment: too loose risks overheating or arcing, too tight can damage the conductor. Never assume factory connections are correctly torqued without checking.

11. Divide the garage into appropriate final circuits

A straightforward garage might contain one lighting circuit, one radial socket-outlet circuit, one dedicated circuit for a fixed appliance, and one external-lighting circuit. A more demanding workshop might need multiple socket circuits, dedicated machinery circuits, three-phase distribution, control circuits, emergency lighting, heating circuits, a dedicated EV charging supply, and future generation or battery connections. Arrange lighting and sockets so that a single fault does not leave the user in complete darkness beside rotating tools, machinery or other hazards.

12. Inspect and test the completed installation

The installation is not complete when the last conductor is connected, it must be inspected and tested to verify the design and installation meet the required safety standards. Depending on the work, testing is likely to include continuity of protective conductors, continuity of ring final circuit conductors where applicable, insulation resistance, polarity, automatic disconnection verification, earth fault loop impedance, prospective fault current, RCD testing, functional testing, verification of protective-device operation, phase sequence where relevant, and confirmation of labels and circuit schedules. Electrium's consumer-unit instructions, for example, state that the installation must be tested after completion in accordance with BS 7671, including verification of RCD/RCBO test functions and satisfactory earth loop impedance.

13. Certify and notify the work

A new garage submain and consumer unit will generally require an Electrical Installation Certificate rather than a Minor Electrical Installation Works Certificate. Where the work falls within the scope of Part P in England, applicable notification requirements must also be considered, Approved Document P covers electrical work associated with dwellings and sets out requirements for design, installation, inspection, testing and the provision of information. Notification arrangements differ across England, Wales, Scotland and Northern Ireland, so follow the rules applicable to where the work is carried out.

The customer should receive appropriate documentation: an Electrical Installation Certificate, schedule of inspections, schedule of test results, Building Regulations compliance certificate where applicable, manufacturer instructions, updated circuit charts and labels, and details of any departures or design assumptions.

Example garage consumer unit arrangement

A typical small-garage design might look like this. This is an example only, protective-device ratings and conductor sizes must be established through design calculations and manufacturer requirements, not copied from a generic table.

Garage consumer unit kits: Wylex and Crabtree

Both brands offer consumer-unit and circuit-protection systems suitable for garages, from small pre-populated "garage kits" for a straightforward two-circuit job, up to larger high-integrity boards for a workshop needing more circuits or future EV/solar provision.

Wylex

For a simple domestic garage needing lighting and one socket circuit, Wylex sells a 2-Way Metal Garage Kit (NMRS206/63GWU, or NMRS206/63GWUA for the Type A RCD version), a compact all-metal enclosure with a 63A 30mA RCD main switch and two pre-installed MCBs, built to BS EN 61439-3. The metal case meets the non-combustible enclosure requirement out of the box. Check the Type A variant where the garage might later feed anything with electronic control circuitry.

Where a garage needs more circuits or individual RCBO protection, Wylex's wider NM range extends to high-integrity boards, the NMRS7SSLMHIA, for example, is a 7-way board with a full metal enclosure, a 100A main switch and two 80A 30mA Type A RCDs (BS EN 61439-3, IP2XC), giving flexible circuit separation, or split-RCD protection so a fault on one side doesn't affect critical circuits like a smoke alarm feed. Choose by actual circuit count, supply rating and RCD strategy, not by whichever board is in stock.

Crabtree

For a small indoor garage installation, Crabtree's Starbreaker range includes a compact 4-Module 2-Way Populated Garage Consumer Unit (502/363GU), a full metal enclosure with a 63A 30mA Type A RCD and two MCBs (6A and 32A), designed for Starbreaker final-circuit devices only. The 32A way gives useful headroom for a socket ring or a smaller EV-adjacent circuit compared with the 16A way found on some equivalent kits.

Worth being upfront about: both of these pre-populated kits use a single shared 30mA RCD feeding two MCB ways, the "lighting and sockets behind one shared RCD" mistake flagged earlier, since a fault on either circuit takes out the whole garage. That's the trade-off for being quick and cheap: fine for a simple garage, but not where the client needs guaranteed independent lighting if the sockets trip. Spec independent RCBOs per circuit instead where that matters.

Larger Starbreaker enclosures add RCBOs, surge protection and AFDD options for workshops needing more circuits, but Crabtree specifies a maximum 63A incomer for its smaller enclosures, so check available ways before assuming a compact board will stretch to cover future circuits.

Choosing between them, and the one rule that matters most

The choice between Wylex and Crabtree should come down to existing equipment, circuit count, incomer rating, RCBO/SPD/AFDD availability, enclosure size and installer familiarity, not brand preference alone.

Whichever system is chosen, use only the devices approved by that manufacturer for the selected consumer unit. A Wylex RCBO in a Crabtree unit, or vice versa, may fit mechanically but can invalidate the assembly's certification and the manufacturer's instructions.

How much does it cost to replace a garage consumer unit?

A straightforward garage consumer unit replacement will commonly cost less than replacing a full domestic consumer unit, because it normally contains fewer circuits. As an indicative UK framework:

Real trade quotes tend to sit consistent with this: a like-for-like board swap with no cabling issues is commonly quoted around £220–£475 installed, and some published 2026 UK pricing guides cite a similar figure, approximately £330–£440, for a small four-circuit garage board replacement including installation, testing, certification and notification. Treat any single figure as an indicative national range rather than a fixed price, and confirm the specific source before quoting it to a client.

Where there's no existing supply and a new sub-main has to be run from the house, real-world quotes commonly land between £1,000 and £1,500+ for a full detached-garage wiring job (board, cable, sockets, lighting) even without major trenching, rising toward the £2,000+ mark on longer cable runs or where a driveway needs cutting.

What affects the cost of a garage consumer unit replacement?

Number of circuits: a two-circuit board needs fewer devices and less testing than one serving lighting, sockets, external equipment, machinery and heating.

RCBO, RCCB or AFDD protection: individual RCBOs normally cost more than a shared RCCB-and-MCB arrangement; AFDD protection adds further equipment cost.

Submain condition: if the existing garage supply is undersized, damaged or incorrectly installed, replacing the consumer unit alone won't resolve the underlying problem.

Cable route: excavation, paving, duct installation, long cable runs and difficult access add substantially to labour and material cost.

Earthing and bonding work: additional earth electrodes, bonding conductors or changes to the earthing arrangement may be required following assessment.

Existing defects: testing may reveal low insulation resistance, incorrect polarity, damaged accessories, unsatisfactory loop impedance or water ingress, none of which should be hidden by simply fitting a new board.

Regional labour rates: London and other high-cost regions typically charge more.

Certification and notification: a professional quotation should state clearly whether inspection, testing, certification and any required notification are included.

How long does it take to replace a garage consumer unit?

A straightforward replacement on an existing compliant supply may be completed within half a day. A more involved installation may take one or more days if it includes a new submain, excavation, new socket and lighting circuits, earthing alterations, fault finding, remedial work, external equipment or workshop machinery. Always allow time for inspection, testing, certification and labelling, these are essential parts of the job, not optional extras.

When should a garage consumer unit be replaced?

Replacement may be advisable where the existing board shows visible burning or overheating, broken covers or exposed live parts, significant water ingress, rewirable fuses, no suitable RCD protection, obsolete protective devices, insufficient capacity, serious mechanical damage, poor-quality alterations, incompatible components, no reliable circuit identification, repeated unexplained tripping, or unsatisfactory test results.

An older plastic enclosure does not automatically mean the entire consumer unit must be replaced, its condition, location and the results of a competent inspection should be considered. The IET advises that consumer-unit safety and replacement decisions should be based on the installation's condition and compliance, rather than age alone.

Can an existing garage fuse box be upgraded without rewiring?

Sometimes. If the existing submain and final circuits are in satisfactory condition and suitable for the new protective devices, the consumer unit may be replaced without a complete garage rewire. However, testing can reveal issues that weren't apparent while the old fuse box was in service, modern RCDs and RCBOs may expose neutral-to-earth faults, insulation deterioration, shared neutrals or leakage from old equipment. A reputable electrician should explain upfront that remedial work may be necessary before all circuits can be safely energised from the new board.

Can a garage consumer unit supply an EV charger?

Potentially, but an EV charger should not simply be added to a garage board because there happens to be a spare way. The designer must assess available supply capacity, maximum demand, load management, submain rating, voltage drop, earthing arrangement, open-PEN protection, RCD requirements, surge protection, circuit selectivity, manufacturer instructions and Building Regulations requirements.

On a PME (TN-C-S) supply in particular, open-PEN fault protection needs specific consideration for EV charge points, an existing garage cable installed years ago for lights and sockets may be entirely unsuitable for a 7kW charger without this being assessed. Future EV charging is worth discussing when the garage supply is first designed, even where the charger won't be fitted immediately.

Can solar panels or a battery connect through the garage consumer unit?

Potentially, but generation and storage introduce additional design requirements: the rating of the consumer unit, the direction and magnitude of current flow, coordination with upstream protection, isolation, labelling, export limitation, earthing, manufacturer requirements, and the effect of multiple supply sources. Where generation operates in parallel with the public supply, the IET notes that the rating of the protective device and generator output must be considered against the rating of the distribution assembly. A standard garage consumer unit should not be assumed suitable for generation or battery equipment without a full assessment.

Common mistakes to avoid

Choosing the cable size by habit. Cable size should be calculated, distance, installation method, load, voltage drop and fault protection all matter.

Installing the smallest available board. A board with no spare capacity makes future additions unnecessarily difficult.

Mixing protective-device brands. Devices must be approved for the consumer-unit system in which they're fitted.

Exporting an earth without assessment. The earthing arrangement must be evaluated, especially in detached buildings with metallic services or outdoor equipment.

Using an indoor board in a damp location. The enclosure must suit the expected environmental conditions.

Placing lighting and sockets behind one shared RCD. A single fault could leave the garage in darkness, consider circuit division and the consequences of unwanted tripping.

Assuming an RCD compensates for poor design. RCD protection doesn't remove the need for appropriate overcurrent protection, earthing, cable sizing and automatic disconnection.

Failing to test the existing circuits. A new consumer unit cannot make defective wiring safe.

Omitting certification. Testing results, an Electrical Installation Certificate and any required notification should form part of the completed job.

Garage consumer unit installation checklist

Before quoting or starting work, confirm:

• Intended garage use and maximum demand

• Existing supply capacity

• Earthing arrangement

• Bonding requirements

• Submain route and installation method

• Cable-size calculations

• Voltage-drop limits

• Fault-current and loop-impedance values

• Consumer unit environmental rating

• Number of circuits and spare ways

• RCD or RCBO type

• SPD requirements

• AFDD assessment

• Circuit division

• Isolation arrangements

• Manufacturer compatibility

• Inspection and testing requirements

• Certification and notification

• Potential future EV, solar or workshop loads

FAQs

How do I wire a garage consumer unit?

Assess the intended load and existing supply capacity, determine the correct earthing arrangement, design and route the submain cable, select a compatible consumer unit with the right RCD/RCBO and SPD protection, wire the final circuits, then inspect, test, certify and notify the completed work.

What size consumer unit do I need for a garage?

It depends on the number of circuits, not the garage's physical size, a simple installation might need two or three circuits, while a workshop may need several dedicated circuits plus spare capacity.

What size cable is needed for a garage consumer unit?

There is no single standard size. It depends on load, run length, installation method, voltage drop, protective device, fault-current conditions, grouping, temperature and future demand, and must be calculated by the designer.

Does a garage consumer unit need an RCD?

Many garage circuits, particularly socket outlets, require 30mA RCD protection under Regulation 411.3.3, the exact arrangement and RCD type depend on the circuit, wiring system and connected equipment.

Does a garage consumer unit need a surge protection device (SPD)?

Since Amendment 2 (September 2022), new consumer unit installations generally require Type 2 SPD protection, check the location and coordination have been properly assessed.

Can I fit a garage consumer unit myself?

No, it requires specialist competence, safe-isolation procedures, test equipment and certification from a qualified electrician who can design, install, inspect, test and certify the work.

Does a detached garage need a separate earth rod?

Not always, the earthing arrangement depends on the supply system, garage construction, conductive services and connected equipment. A separate electrode may suit some installations, but it isn't a universal rule.

Can I run a garage consumer unit from a socket circuit?

No, a garage supply should be designed for the expected load and protected at its origin, not extended from an existing socket circuit.

Can I use a plastic consumer unit in a garage?

Generally not for domestic installations, BS 7671 favours a non-combustible enclosure, and environmental and impact risk must also be assessed for the location.

How much does it cost to replace a garage consumer unit?

Roughly £300–£500 for a like-for-like board swap on an existing compliant supply; £600–£1,000+ for a new board and short submain; and £1,000–£2,500 or more where excavation or a long SWA run is needed.

Can a garage consumer unit supply an EV charger?

Potentially, but it needs a full assessment of supply capacity, cable rating, voltage drop, earthing and open-PEN protection, a cable installed for lights and sockets may not suit a 7kW charger without upgrading.

Will replacing the garage consumer unit stop nuisance tripping?

Only if a defective or poorly configured consumer unit is actually the cause, faulty wiring, moisture ingress, excessive leakage or an overloaded circuit are equally likely, so test and find the fault before replacing.

The bottom line

Understanding how to wire a garage consumer unit begins with proper electrical design. The installer must assess the expected load, existing supply, cable route, earthing arrangement, protective devices, enclosure conditions and future requirements before any equipment is selected.

For many modern garage installations, a metal consumer unit with compatible Type A RCBOs, appropriate surge protection and spare capacity provides effective circuit separation and flexibility. Wylex and Crabtree both offer product systems worth considering, from compact pre-populated garage kits for a simple two-circuit job, up to high-integrity boards for a workshop, provided the complete assembly is selected and installed strictly in accordance with the manufacturer's instructions.

The final installation should always be inspected, tested, labelled, certified and notified where required.