BS 7671 Amendment 4: Battery Storage Requirements

When I sized the battery backup circuit for our SAG mill control system at the mine, the standard didn't have dedicated battery requirements. Amendment 4 finally addresses this.

Why Dedicated Battery Requirements?

The rapid growth of battery energy storage systems (BESS) — from domestic solar batteries to grid-scale installations — has exposed gaps in existing wiring regulations. Until Amendment 4, designers had to cobble together guidance from general installation rules, manufacturer instructions, and non-UK standards. The new chapter provides a unified framework for stationary secondary battery installations.

Installation Requirements

Amendment 4 introduces specific requirements for battery room ventilation, containment, and location. Installations must account for hydrogen gas production in lead-acid systems, thermal runaway risk in lithium-ion systems, and electrolyte leakage in all chemistries. Minimum clearances, fire-rated enclosures, and access requirements are defined for each installation type.

Isolation & Labelling

Clear isolation and labelling requirements address a key safety concern: battery systems cannot be de-energised by simply opening an upstream breaker. Amendment 4 mandates DC isolation devices at the battery, clear danger notices at all points of isolation, and labelling of stored energy hazards visible to emergency responders.

Protection Requirements

Protection coordination for battery circuits requires consideration of both AC and DC fault characteristics. The amendment covers overcurrent protection, earth fault detection, and the specific challenges of DC arcing. Designers must demonstrate that protective devices can safely interrupt prospective fault currents from the battery bank.

Related Standards

The new chapter aligns with IEC 62619 (safety requirements for lithium secondary cells), IEC 62485-2 (safety requirements for secondary batteries — stationary), and the relevant parts of BS EN 50549 for grid-connected storage. Designers should reference these in conjunction with the BS 7671 requirements.