Electric Vehicle Power Distribution

Residential AC EV Chargers are limited to 7.2kW, which at 230V equates to 31.3A. With residential EV Chargers limited to 32A, a typical full charge could take up to 4 hours at a
constant 32Amps. When designing the installation, consideration should be given to potential derating factors for the distribution board, the RCD and MCB plus the final circuit cabling installation.

To meet the installation requirements detailed above, it may be necessary to utilise a 10mm2 cable possibly even a SWA cable. To help terminate the cable, the choice of an RCCB fed by a MCB for the load side cabling provides for greater cable capacity than an RCBO, as well as an easier installation.

In terms of residual current protection, the key consideration of circuits containing EV chargers is the potential presence of higher levels of DC fault currents which can have a major effect upon the operation of RCD’s. BS7671 Section 722 covers the requirements for the installation of EV Charging Installations with specific focus upon the use of RCD’s and the potential presence of DC fault currents exceeding 6mA. 722.531.3.101 requires protection to be provided against DC fault currents exceeding 6mA. and states the following:

Each charging point incorporating a socket-outlet or vehicle connector complying with the BS EN 62196 series shall be protected individually by an RCD of Type A, Type F or Type B and having a rated operating current not exceeding 30mA. Except where provided by the EV charging equipment, protection against DC fault currents shall be provided by:

(i) an RCD Type B, or
(ii) an RCD Type A or Type F in conjunction with a residual direct current detecting device (RDC-DD)

Note (i): A Type B RCD can operate with DC fault currents in excess of 6mA
Note (ii): An RDC-DD is a Residual Direct Current - Detecting Device which has been designed to meet BS IEC62955 for use with permanently connected AC electric vehicle charging stations (Mode 3) and provides the functionality of detecting DC residual currents equal to or above 6mA and switching off the monitored circuit.

Therefore, protection against DC fault currents exceeding 6mA can be achieved, by either installing a Type B RCD at the origin of the installation, Or, as it becomes more common, for the EV charger to include an RDC-DD, allowing the upstream RCD to be a Type A RCD. To meet both of these options, the new range provides for the choice of Type A or Type B RCD protection.