BS 7671 Amendment 4 Is Coming in April 2026 — Here's What Changes for Practising Engineers

If your design software still says "17th Edition" anywhere on the report, read this before your next UK project. Amendment 4 to BS 7671:2018 is scheduled for publication in April 2026, and it is not a cosmetic update. Several regulation changes will directly affect circuit design decisions that engineers make every day — particularly around arc fault detection, EV charging infrastructure, and photovoltaic installations.

I have been tracking the IET technical committee discussions and the draft consultation documents. What follows is a practical summary of what is changing, why it matters, and what you need to do before the transition deadline.

Amendment 3 introduced Arc Fault Detection Devices (AFDDs) as a recommended measure in certain premises. Amendment 4 goes further, making AFDDs mandatory in specific zones:

• Houses in Multiple Occupation (HMOs): All final circuits in sleeping accommodation and common areas must now be protected by AFDDs complying with BS EN 62606. This directly addresses the fire risk in shared housing where maintenance oversight is often poor.
• Care homes and sheltered accommodation: AFDD protection extends to all final circuits, not just those serving sleeping areas. The rationale is the reduced ability of occupants to self-evacuate.
• Timber-framed buildings: New construction using structural timber frames must have AFDD protection on all circuits within the timber envelope. This aligns with the fire safety strategy required by Building Regulations Approved Document B.
• Student accommodation: University and college residential blocks are now explicitly included in the AFDD requirement, closing a gap in Amendment 3.

The practical impact is significant. For a typical HMO conversion, AFDD protection adds between 800 and 1,500 GBP to the consumer unit cost, depending on the number of circuits. Designers need to factor this into project budgets from the feasibility stage.

Amendment 4 introduces minimum circuit requirements for EV charging installations that go beyond what was previously covered by BS 7671 and IET Guidance Note 12:

• Minimum cable rating: Dedicated EV circuits must be sized for a minimum of 32 A continuous load, even if the charger currently installed draws less. This future-proofs the installation for charger upgrades without rewiring.
• Cable route requirements: The cable route from the distribution board to the charge point must be designed for replacement without structural work. This means either conduit, trunking, or accessible surface routes — not cables buried in plaster.
• PME earthing: The existing requirements around PME earthing and EV charging are consolidated and clarified. Where the supply is PME, an earth electrode or alternative earthing arrangement must be provided at the charge point. The regulation now explicitly states the minimum earth electrode resistance values required.
• Load management: Where multiple EV charge points are installed, dynamic load management (per BS EN 61851-1) becomes mandatory rather than recommended. Static diversity assumptions are no longer acceptable for installations of four or more charge points.

For commercial installations with multiple charge points, the load management requirement fundamentally changes how maximum demand calculations work. The old approach of applying a diversity factor from IET Guidance Note 1 Table 1A is no longer sufficient — you need to demonstrate that a compliant load management system is specified.

Section 712 (Solar Photovoltaic Power Supply Systems) has been substantially rewritten. The 2018 text was drafted when rooftop PV was still relatively uncommon in the UK. In 2026, with over 1.5 million domestic PV installations, the regulations needed to reflect current practice:

• Battery energy storage: The scope of Section 712 now explicitly covers battery energy storage systems (BESS) connected to PV arrays. Previously, BESS fell into a regulatory grey area between BS 7671 and BS EN 62619. The new text provides clear requirements for DC isolator positions, overcurrent protection, and cable sizing for battery circuits.
• String cable sizing: A new table provides minimum string cable sizes based on module short-circuit current (I_sc) and expected rooftop ambient temperature. The derating methodology specifically accounts for the elevated temperatures found on rooftops — up to 70°C in UK summer conditions for dark roof coverings.
• Rapid shutdown: While not adopting the NEC 690.12 rapid shutdown requirement directly, Amendment 4 introduces a recommendation for module-level disconnect capability on systems above 3 kW_p. This is expected to become mandatory in the 19th Edition.

The transition period for Amendment 4 follows the pattern established by previous amendments:

1. Publication date (April 2026): The amendment is published and available for immediate use.
2. Co-existence period (April 2026 – September 2026): Designs may comply with either Amendment 3 or Amendment 4. Both are considered compliant during this period.
3. Mandatory adoption (October 2026): All new installations must comply with Amendment 4. Designs already in progress under Amendment 3 may continue provided installation is substantially complete by December 2026.

The six-month co-existence period is shorter than the twelve months allowed for Amendment 3. The IET has stated that this reflects the maturity of the industry and the fact that most of the changes are additions rather than contradictions to existing regulations.

For practising engineers, the critical action is to update your design templates, calculation tools, and specification documents before October 2026. Any project starting design after April 2026 should use Amendment 4 to avoid the risk of non-compliance at installation stage.

Between now and April 2026, there are practical steps to prepare:

• Audit your standard templates: Check every design template, specification clause, and report header for references to the BS 7671 edition. Update them to reference "BS 7671:2018+A4:2026" once the amendment is published.
• Review HMO and care home projects: If you have projects in design for these building types, check whether the additional AFDD cost is included in the budget. Flag it to the client early rather than as a variation later.
• EV charging specifications: Update your standard EV charging specification to include the 32 A minimum circuit rating and dynamic load management requirements. The cost difference at cable stage is minimal — the difference at the load management stage is not.
• PV design procedures: If you design PV installations, review your cable sizing methodology against the new Section 712 requirements. The rooftop temperature derating is likely to increase cable sizes on some installations.
• Update your calculation tools: Ensure your cable sizing software can reference the correct tables and derating factors for Amendment 4.

ECalPro supports BS 7671:2018+A4 from the date of publication. You can run calculations under both Amendment 3 and Amendment 4 to compare results and identify which circuits are affected by the changes. Try a cable sizing calculation under BS 7671 to see how the updated derating factors affect your next UK project.