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

A2 was the largest update since the 18th Edition itself — reshaping SPDs, AFDDs, EV charging, prosumer installations and adding the new Operational Technology section.

1. 1

   AFDDs (Regulation 421.1.7) — recommended, not mandatory

   A2 softened the 18th Edition A1 stance: AFDDs are recommended for single-phase AC final circuits supplying socket-outlets ≤ 32 A in higher-risk locations (HMOs, care homes, purpose-built student accommodation, high-rise residential over 18 m). Elsewhere, a risk assessment determines their use.

2. 2

   SPDs (Section 443) — protection now the default

   The old 'CRL' risk calculation was removed. SPDs must be provided unless the owner declares in writing that they accept the risk of loss/damage (excluding risk to human life, safety services, or where the CRL would still require protection). Regulation 443.4.1 lists where SPDs are always required.

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

   Section 730 — Operational Technology (new)

   A brand-new section covering LV networks that support process control, building automation and other operational technology — recognising these as safety-critical infrastructure separate from general LV distribution.

5. 5

   Prosumer installations (Section 826) — new definitions

   Definitions for prosumer electrical installations (PEI) — installations that both consume and produce electricity — were added, laying the groundwork for the A4 battery storage rules.

6. 6

   Energy efficiency (Chapter 82) — expanded

   Guidance in Appendix 17 (energy efficiency) was elevated and expanded — cable sizing, transformer selection, power factor and load management now form part of the design assessment.

7. 7

   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 declaration process. The default remains: fit SPDs unless the client accepts the risk in writing.

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