As a general rule of thumb, a standard 7kW single-phase home EV charger runs on a 32A circuit breaker, and a 22kW three-phase unit typically needs a 32A breaker per phase. But that’s a starting point, not a spec you should work to directly – the actual figure for your installation depends on several things that a qualified electrician needs to calculate properly, not estimate from a rule of thumb.
Why It’s Not Just About the Charger’s Power Rating
The right breaker size, and the cable that goes with it, depends on the charger’s power output, the length and route of the cable run from your consumer unit, the type of earthing arrangement your property has (TN-S, TN-C-S or TT – which affects how the circuit is protected), and how much spare capacity your existing consumer unit and incoming supply actually have once your other household loads are accounted for. Section 722 of BS 7671, the part of the UK wiring regulations specifically covering EV charging installations, sets out how all of this needs to be assessed.
What Happens If It’s Undersized
A breaker that’s too small for the load will trip repeatedly under normal charging, which is a nuisance but not dangerous. A breaker that’s too large for the cable it’s protecting is the genuinely dangerous scenario – it can allow a cable to overheat under fault conditions without tripping in time, which is exactly the kind of thing an EICR is designed to catch afterwards if it’s ever done incorrectly.
Protective Devices Beyond the Breaker
EV circuits also need appropriate residual current protection – usually a Type A or Type B RCD, or protection built into the charger itself – because of the type of DC leakage current an EV charging process can produce, which a standard RCD isn’t always designed to detect. This is one of the more common things an inexperienced installer gets wrong, and it’s a safety-critical detail, not a technicality.
Why This Needs a Proper Assessment, Not a Guess
Because the right answer depends on your specific property – supply capacity, existing loads, cable route and earthing arrangement – this is one of those questions where a confident-sounding number from a forum or a generic guide (this one included) shouldn’t be treated as the final answer for your installation. We’ll assess your consumer unit and incoming supply properly before recommending a circuit design, as part of every EV charger installation we carry out.
What We Check Before Recommending a Circuit
Before quoting for an installation, we’ll look at your existing consumer unit’s spare capacity, the type of earthing your property has, the practical cable route from the consumer unit to where the charger will sit, and what other significant loads are already on your supply. This is a five-minute check for us, but it’s the difference between a circuit that’s sized correctly from day one and one that causes nuisance tripping, or worse, later on.
Get in touch and we’ll take a look at your setup and tell you what’s actually needed.