BS 7671 Amendment 4: Domestic EV Charger Installation

Domestic EV charging installation has been guided by IET Code of Practice for EV Charging Equipment Installation since 2012, with BS 7671 providing the underlying wiring rules. Amendment 4 incorporates key EV charging requirements directly into the standard, reducing reliance on the separate Code of Practice and ensuring consistent interpretation.

The most debated topic in domestic EV charging — PME earthing — receives definitive treatment. Amendment 4 clarifies the conditions under which EV charging equipment may be connected to a PME (TN-C-S) earthing system without additional earth electrode provision. The three conditions are: the EVSE must incorporate PEN fault detection, the EVSE must be Type A or Type B RCD protected (Type AC is explicitly prohibited), and the installation must have a main protective bonding conductor of at least 10 mm² copper. Where any condition is not met, a separate earth electrode is required per the established practice.

Load management is addressed for the first time in BS 7671. With domestic EV chargers drawing up to 7.4 kW (32A single-phase) from a typical 100A single-phase supply, the interaction with other high-demand loads (electric showers, cookers, heat pumps) is critical. Amendment 4 recommends dynamic load management where the EVSE communicates with the main incoming supply monitoring to reduce charging current when other demands peak. This is a recommendation, not a requirement, but it enables the DNO to avoid supply upgrades.

Circuit design for domestic EV charging must now consider the potential for simultaneous battery storage and solar PV generation. Amendment 4 cross-references Chapter 57 (battery storage) and Chapter 72 (solar PV) for installations where all three technologies coexist. The consumer unit must accommodate the additional circuit protection and isolation requirements of all three systems, which may require a larger enclosure or a sub-distribution board.

Cable sizing for the EV circuit must use the continuous rating of the EVSE. Most domestic chargers operate at full rated current for extended periods (4-8 hours for a full charge), so the cable must be sized for the continuous rating, not a diversity-reduced figure. Amendment 4 explicitly states that no diversity factor shall be applied to a single domestic EVSE circuit.

ECalPro's EV Charging Calculator handles domestic EV circuit design per Amendment 4, including PME earthing assessment, cable sizing without diversity, and load management integration.