EV Charging Installation Guide for Electricians
Electric vehicle charging is now routine electrical work, but it has traps that catch installers who treat a charger like any other fixed appliance: sustained high loads for hours, DC leakage currents that blind ordinary protection, and vehicles that negotiate power with the charger. This guide walks through the decisions in order — charger type, supply capacity, protection, installation and commissioning — for domestic and small commercial installations. Always work to the applicable wiring regulations and the charger's manufacturer instructions, which govern over any general guide.
Charger levels: what the options mean
Slow AC charging from an ordinary socket outlet is the fallback, not the plan: it is slow, it ties up a general-purpose circuit for hours, and it is not designed for sustained load. A dedicated AC charge point is the standard domestic and workplace solution, typically delivering around 7 kW on a single-phase supply and up to around 22 kW on three-phase, charging most cars overnight. DC fast charging bypasses the car's onboard charger and feeds the battery directly at much higher power — tens to hundreds of kilowatts — and belongs to public and fleet sites, not homes: it needs a large supply, specialist equipment and a very different commercial case. The choice for a given site follows from two questions: how much energy does the vehicle need per day, and how many hours is it parked? A car that covers a daily commute and parks overnight is served perfectly by a 7 kW AC point; a fleet vehicle with a short turnaround is not.
Supply capacity and load management
A charger is a large, sustained load, and the first job is checking whether the supply can carry it alongside everything else. Assess the existing maximum demand, the supply fuse rating, and the diversity of the rest of the installation — a 7 kW charger on a 60 A single-phase supply alongside electric heating and cooking needs careful thought. Where the supply is tight, load management is the answer rather than an expensive upgrade: a charger with load balancing monitors the total site demand and throttles charging to stay within the supply limit, and multiple chargers can share a capped total between vehicles. Record the assessment and the settings; the next electrician to visit the site needs to know the charger is deliberately limited and why.
Protection: earthing and DC leakage
EV charging has two protection issues that ordinary circuits do not. First, earthing: a fault in the vehicle or charger can raise the vehicle's body and the charger enclosure to a dangerous voltage relative to true earth, and the usual protective measures for a domestic supply do not always cover the case where the supply earth itself is lost. The charger's manufacturer instructions and the wiring regulations set out the accepted arrangements — which may include a dedicated earth electrode, a device that monitors the supply earth and disconnects on failure, or connection to a suitable earthing system — and the chosen arrangement must be recorded and tested. Second, DC leakage: a fault in a vehicle can leak smooth DC current that blinds an ordinary AC residual current device, so EV circuits need DC-tolerant protection, either built into the charger or provided as a suitable RCD type. Never assume the protection inside the charger covers the whole circuit; check what the manufacturer provides and what the circuit still needs.
Site survey and installation practice
Survey before you quote, not after you arrive. Cable route and length decide voltage drop and cost; the charger location decides weather exposure, vehicle access, cable trip hazards and vandalism risk; the consumer unit's spare ways, condition and age decide whether the new circuit is straightforward or a board change. Install the charger on a dedicated circuit, sized for continuous load — a charger runs at full current for hours, so the usual assumptions about intermittent loads do not apply — with the cable installed to suit its environment and protected against mechanical damage where vehicles move. Label the circuit clearly at the board, and leave the user instructions where the user will find them, not in the box.
Commissioning tests and handover
Commissioning proves the installation works and is safe. Test insulation resistance, earth fault loop impedance and RCD operation including the DC protection, verify the charger communicates with the vehicle (or a test load) and delivers the expected current, and confirm load management behaves as designed by applying a competing load and watching the charger throttle. Record all results on the installation certificate, demonstrate the charger to the user — how to start and stop a charge, what the indicator lights mean, what to do if it faults — and explain the load-management limit if one is set, so the user is not surprised by a slower-than-expected charge on a busy evening. A charger that the user understands is a charger that stays in use; one that baffles them gets bypassed or abandoned.