Wiring Regulations (BS 7671) 18th Edition — Amendments 2, 3 & 4

A2 was the largest update since the 18th Edition itself — reshaping SPDs, AFDDs and EV charging, and adding the brand-new Part 8 for prosumer installations.

1. 1

   AFDDs (Regulation 421.1.7) — mandatory in higher-risk premises

   A2 retained the A1:2020 'shall' requirement: AFDDs are mandatory for single-phase AC final circuits supplying socket-outlets ≤ 32 A in higher-risk residential buildings over 18 m, HMOs, purpose-built student accommodation and care homes. Elsewhere they remain recommended, with a risk assessment determining their use. See the shall/recommended timeline below.

2. 2

   SPDs (Section 443) — protection now the default

   The old 'CRL' risk calculation was removed. SPDs must be provided unless the owner of the installation decides the risk of loss/damage is acceptable (excluding risk to human life and safety services, where SPDs are always required). Regulation 443.4 lists where SPDs are mandatory.

3. 3

   EV charging (Section 722) — PME open-PEN restrictions

   Regulation 722.411.4.1 permits PME earthing for EV points only when open-PEN detection cuts the L+N+PE within 5 s at ≥ 70 V rms, or when the installation uses a TT earthing arrangement. This is the reason most modern EVSE either has built-in PEN fault detection or is installed on a dedicated earth rod.

4. 4

   Part 8 / Chapter 82 — Prosumer electrical installations (new)

   A completely new Part 8 covering prosumer electrical installations (PEI) — installations that both consume and produce electricity (PV, battery storage, generators, V2X). Chapter 82 sets out how generating equipment integrates safely with the LV installation, laying the groundwork for the A4 battery storage rules.

5. 5

   Appendix 17 — Energy efficiency (expanded)

   The energy-efficiency guidance in Appendix 17 was expanded — cable sizing, transformer selection, power factor and load management now form part of the design assessment.

6. 6

   Fire safety — Regulation 421.1.201

   Metal consumer units / similar switchgear assemblies in domestic (household) premises must still be non-combustible — clarified and retained.

A short amendment focused on bidirectional protective devices and housekeeping ahead of A4. Issued free of charge and consolidated into A4.

1. 1

   Bidirectional protective devices — new definitions

   A3 introduces formal terminology for 'unidirectional' and 'bidirectional' protective devices. This matters where an additional power source (PV, battery storage, generator, EV V2X) can back-feed a circuit — the device must interrupt fault current arriving from either direction.

2. 2

   Section 712 (PV) — aligned wording

   Wording was aligned with the bidirectional terminology so that PV strings feeding into an inverter downstream of the CU are correctly classified.

3. 3

   Section 722 (EV) — minor clarifications

   Small wording tidy-ups to the EV section ahead of the larger Section 722 rewrite delivered in A4.

4. 4

   Housekeeping across Parts 1–7

   A3 is primarily a technical corrigendum plus the bidirectional-device work. It was issued as a free download and is fully absorbed into A4.

A4 delivers Chapter 57 for battery storage, a rewritten EV section, and — for the first time — brings PoE and structured cabling into the scope of the Wiring Regulations.

1. 1

   Chapter 57 — Electrical Energy Storage Systems (new)

   A dedicated chapter for battery energy storage systems (BESS). Covers selection & erection, isolation, protection against thermal runaway, ventilation, location (habitable vs non-habitable rooms), signage, and coordination with PV/EV/grid-tied inverters. This is the single biggest addition in A4.

2. 2

   Section 722 — EV charging rewritten

   Consolidates all EV requirements including bidirectional (V2G/V2H) charging, integration with BESS and PV, refined PME/open-PEN rules, and updated selection of RCDs (Type B or equivalent) for DC fault current management.

3. 3

   New requirements for PoE and ICT power

   Introduces earthing, bonding and current-carrying requirements for Power-over-Ethernet and other low-voltage ICT power distribution — bringing structured cabling squarely into scope of the Wiring Regulations for the first time.

4. 4

   AFDDs — expanded scope under review

   Regulation 421.1.7 is retained. Industry consultation during the DPC suggested widening AFDD scope; the published A4 keeps the 'recommended' language but adds clearer criteria for the risk assessment. Watch for further guidance.

5. 5

   SPD requirements — clarified

   Section 443 wording was tightened around consequences of loss of service and the risk-acceptance process. The default remains: fit SPDs unless the client decides the risk is acceptable (safety services and risk to human life excepted).

6. 6

   Consolidation of A3

   All A3 bidirectional-device wording is now fully embedded in the main text — you no longer need to cross-reference the A3 corrigendum once you are working to A4.

7. 7

   Publication & effective dates

   Published 15 April 2026. Designs from 15 October 2026 must comply with A4. Installations designed before that date may still be certified to A2/A3 provided design records exist.

BS 7671 uses very specific verbs, and they carry very different weight. The headline change most electricians ask about is the AFDD wording under Regulation 421.1.7 — here is the timeline in plain English.

The definitive text is the printed standard from the IET / BSI. The links below go to the primary sources used to compile this page.

• IET — BS 7671 product page
• IET — Amendment 4 information hub
• IET — Amendment 3 (2024) free download
• BSI Knowledge — BS 7671:2018+A2:2022
• Electrical Safety First — Resources for Electricians
• Electrical Safety First — Best Practice Guides
• GOV.UK — EV Charge Point Regulations 2021