BS 7671 Amendment 4 (April 2026): What's Changing and What You Need to Do Now

The headline changes fall into four areas, each responding to how UK electrical installations have shifted since Amendment 3 landed in 2024.

Expanded AFDD requirements

Regulation 421.1.7 broadens its scope. Amendment 3 targeted socket-outlet circuits in dwellings and sleeping accommodation. Amendment 4 extends AFDD requirements to:

• Final circuits in commercial premises with combustible contents (retail stockrooms, archive stores, workshop areas with timber or paper products)
• Circuits supplying outdoor or temporary installations connected to permanent supplies — directly responding to fire incidents at festivals and construction sites
• Socket-outlet circuits in educational buildings where children under 16 are present

The risk assessment exemption from Amendment 3 remains, but the IET Guidance Note 3 update tightens the criteria for what constitutes an acceptable risk assessment. Expect scrutiny on any installation that claims exemption without documented justification.

Prosumer battery storage — Section 722 revision

The domestic battery storage market has outpaced the standards framework. Section 722 now includes specific provisions for:

• Battery energy storage system (BESS) disconnection requirements — both AC and DC isolation points
• Overcurrent and fault protection for DC circuits between battery modules and inverters
• Earthing arrangements for hybrid AC/DC prosumer installations, addressing the risk of transferred potentials between the AC supply earth and the DC battery system
• Labelling requirements at the consumer unit, meter position, and battery enclosure — critical for firefighter safety during dwelling fires

EV charging — HD 60364-7-722 alignment

The UK’s EV charging requirements have diverged from the European HD 60364-7-722 framework since Brexit. Amendment 4 re-aligns on key technical points:

• DC fault current detection requirements for Mode 3 charging (Type 2 connectors) now reference IEC 62955 residual current devices with DC detection capability, rather than relying solely on Type B RCDs
• Cable sizing for EV circuits explicitly accounts for continuous load at rated current — the 100% load factor that catches designers who apply diversity to EV circuits as if they were socket-outlets
• Maximum demand contribution for EV chargers updated to reflect real-world usage data: 7 kW single-phase units at 60% diversity for residential, 100% for commercial rapid chargers

Revised EMC provisions

Modern installations are dense with power electronics: inverters, VFDs, LED drivers, EV chargers, battery converters. Amendment 4 introduces:

• Cable segregation categories updated to include DC power circuits alongside the existing AC categories
• EMC coordination requirements for installations with multiple inverter-based sources (solar PV + battery + grid)
• Harmonic current provisions referencing IEC 61000-3-2 thresholds, relevant for neutral conductor sizing in three-phase installations with non-linear loads

Based on the published IET roadmap and JPEL/64 committee minutes:

What to do now:

1. Review your AFDD specification templates. If you design for commercial or educational premises, you will need AFDD provisions on socket-outlet circuits. Update your standard specifications before the effective date, not after.
2. Train on prosumer battery installations. If you have not designed a BESS installation under the new Section 722 provisions, start now. The EAL/City & Guilds 2399 qualification is being updated for Amendment 4 — book early.
3. Audit your EV charging designs. Check that your standard EV circuit design accounts for 100% load factor (no diversity on single charger installations) and that DC fault detection is specified for Mode 3 connections.
4. Neutral conductor sizing. For three-phase installations with significant non-linear loads (LED lighting, VFDs, EV chargers), verify that neutral conductors are sized for triplen harmonic currents. The old assumption that neutral current is negligible in balanced three-phase systems does not hold with modern loads.

Standards referenced: BS 7671:2018 Amendment 4:2026 (expected), HD 60364-7-722, IEC 62955, IEC 61000-3-2, BS EN 62606.