Sizing the circuit and cable run for an EV charger
The dedicated EV charger circuit is sized for the charger's load and the length of the run. A 7.4kW single-phase charger draws about 32A, so it's protected by a suitably rated device (commonly a 32A) and wired in cable sized to carry that current safely by the installation method and then checked for voltage drop over the run, because a long cable run to a charge point at the end of a drive can force a larger cable than the current alone would need. It needs RCD protection of the correct type (Type A with 6mA DC detection, or Type B) and the open-PEN protection Irish PME supplies require. The exact cable size comes from the design to IS 10101 by the electrician, factoring load, method, grouping and run length.
The EV charger's own circuit is a small piece of the installation, but it has to be sized correctly and the length of the run to the charge point often matters as much as the load. This is about the dedicated EV circuit specifically, and how the cable and protection are chosen for it, as supplied by Waveform Electrical Wholesale. (The wider consumer unit and RCD principles are a separate topic.)
Sizing for the charger
The circuit is designed around the charger's demand. A 7.4kW single-phase charger draws roughly 32A continuously, so the protective device is rated to suit (commonly 32A), and the cable must be able to carry that current safely for the way it's installed. Because an EV charger draws its load for hours at a time, the circuit is designed with that continuous duty in mind rather than a brief peak.
Cable size and the run
Cable size follows two checks. First, the cable must carry the current safely given the installation method (clipped, in conduit, buried) and any derating for grouping or temperature. Second and this is where EV circuits often catch people out voltage drop over the length of the run must stay within limits. A charge point at the far end of a long driveway can be a substantial cable run, and voltage drop over that distance can require a larger cable than the current alone would suggest. The run length is a real factor, not an afterthought.
RCD type and protection
- RCD protection of the correct type: Type A with 6mA DC detection, or Type B, as required by the charger and IS 10101 (a standard RCD alone is not sufficient for EV).
- Correct overcurrent protection for the circuit.
- Open-PEN protection for the PME (TN-C-S) supply, via a charger with built-in protection or an earth electrode arrangement.
- Coordination with the consumer unit and the overall installation.
Designed to the standard
Pulling it together, the EV circuit's cable and protection are designed to IS 10101 for the specific charger, installation method and run length which is why it's an electrician's calculation, not a fixed answer. Note the RCD requirement in particular: EV circuits need a specific type of protection, not just any RCD. WEW supplies EV chargers, cable, RCDs and consumer unit components across Meath see what an EV charger installation involves for the full process. Design and install by a Safe Electric registered electrician.
Frequently asked questions
What size cable does an EV charger need?
It depends on the charger load, the installation method and the run length. A 7.4kW charger draws about 32A, so the cable must carry that safely and then pass a voltage-drop check over the run a long run to a charge point can require a larger cable than the current alone would need. The exact size is designed to IS 10101 by the electrician.
Why does the cable run length matter for an EV charger?
Because voltage drop increases with the length of the run, and it must stay within limits. A charge point at the far end of a long driveway can be a substantial cable run, and the voltage drop over that distance can force a larger cable than the current-carrying requirement alone would suggest.
What RCD does an EV charger need?
RCD protection of the correct type - Type A with 6mA DC detection, or Type B as required by the charger and IS 10101. A standard RCD alone is not sufficient for EV charging. The circuit also needs the open-PEN protection Irish PME supplies require, designed by the installer.
Source it at WEW
WEW (Waveform Electrical Wholesale) is your electrical wholesaler and lighting expert in Meath, supplying fans, ventilation, EV charging and everything electrical to trade and homeowners. Call in to the counter or the showroom for stock, advice and everything referenced in this guide.