BS 7671:2018+A4:2026 Wiring Regulations: Key Changes Guide

Summary

BS 7671 — the IET Wiring Regulations — is the technical standard for electrical installations in the UK. It is not a statutory document but is referenced by Building Regulations (Part P), and compliance is considered necessary evidence of safe installation. Courts treat non-compliance as strong evidence of negligence.

The 18th Edition (published 2018) introduced significant changes from the 17th Edition, including stronger RCD requirements, AFDD recommendations, and new sections for special locations. Amendment 1 (2020), Amendment 2 (2022), Amendment 3 (2024) and Amendment 4 (2026) introduced further updates — Amendment 3 added provisions for bidirectional protective devices (relevant to solar/battery installations with multiple current sources), and Amendment 4 introduced mandatory domestic lighting-circuit RCD protection, an expanded AFDD mandate for higher-risk residential premises, and a new chapter on stationary secondary batteries. All electricians must work to the current version.

Key Facts

• Current standard: BS 7671:2018+A4:2026 (18th Edition + Amendment 4). Published by the IET and BSI on 15 April 2026 and usable immediately; the prior BS 7671:2018+A2:2022+A3:2024 combination is withdrawn on 15 October 2026 after a six-month transition window.
• Produced by: IET (Institution of Engineering and Technology) and BSI.
• Legal status: Not statute but referenced by Building Regs. Non-compliance with BS 7671 is prima facie evidence of non-compliance with Part P and the Electricity at Work Regulations 1989.
• RCD protection (Chapter 41 + 531): Most final circuits in domestic premises require 30mA RCD protection. As of Amendment 4, a new Regulation 411.3.4 makes 30mA RCD additional protection mandatory for AC final circuits supplying luminaires (lighting) in domestic premises — previously this was only a strong recommendation. Types: RCBOs (per-circuit); split-load consumer unit (some RCD protection only); fully RCD-protected consumer unit. Current practice strongly favours individual RCBO protection per final circuit.
• AFDD (Arc Fault Detection Devices): Amendment 4 makes AFDD protection mandatory for socket-outlet final circuits (≤32A) in Higher Risk Residential Buildings, HMOs, purpose-built student accommodation, and care homes. For ordinary single-household domestic dwellings, AFDDs remain a strong recommendation (Regulation 421.1.7) rather than a requirement — bedrooms/sleeping areas as a minimum — but inspectors increasingly expect them on new full rewires.
• SPD (Surge Protection Devices): Required (Regulation 443) where loss of installation would have serious consequences or where replacement cost is high (most new domestic installs justify this). Note: risk assessment required but most domestic installations now warrant SPD provision.
• EV charging: Regulation 722 (Section 722) covers EV charging points. Requirements: dedicated circuit, appropriate EVSE (Electric Vehicle Supply Equipment), earthing arrangement. Mode 3 charging (dedicated EVSE with control pilot) is the standard for domestic wallbox.
• Cable sizing: Calculated using BS 7671 Appendix 4 (current-carrying capacity tables) accounting for installation method, grouping, and thermal insulation.
• Earth fault loop impedance (Zs): Must be verified against Table 41.2 to confirm protective device will disconnect within the required time (0.4s for socket outlets in TN systems; 5s for distribution circuits).
• Periodic inspection: Domestic: 10 years or on change of occupancy. Rental: 5 years (mandatory under Electrical Safety Standards in the Private Rented Sector Regulations 2020).
• EIC / EICR: Electrical Installation Certificate on completion of new work. Electrical Installation Condition Report for periodic inspection.

Quick Reference Table: Key 18th Edition Changes from 17th Edition

Detailed Guidance

RCD Protection Requirements

The 18th Edition (and especially Amendments 1, 2 and 4) strengthens RCD requirements significantly:

Socket outlets (Regulation 411.3.3):

• All socket outlets in domestic premises rated ≤20A must have 30mA RCD protection
• Exception: where documented risk assessment determines it unnecessary (very limited)

Lighting circuits (Regulation 411.3.4 — new in Amendment 4:2026):

• Additional protection by a 30mA RCD is now required for AC final circuits supplying luminaires (lighting points) in domestic (household) premises
• This closes a long-standing gap: lighting circuits were previously the main domestic circuit type that could be installed without RCD protection
• Applies to new circuits designed to +A4:2026; existing lighting circuits are not required to be retrofitted unless other notifiable work is being carried out on them

Cables concealed in walls (Regulation 522.6.202):

• Unless protected by earthed metallic covering, cables concealed in walls must be:
  • At ≥50mm from surface, OR
  • Protected by earthed metallic conduit, OR
  • Protected by 30mA RCD

New circuits — recommended approach:

• Individual RCBO per final circuit in new or replacement consumer units
• Avoids discrimination problems (single RCD tripping and taking out many circuits)
• Provides best fault discrimination

Types of RCD for domestic use:

• Type A: Detects sinusoidal AC residual current + pulsating DC residual current. Required where electronic loads (inverters, EVSEs) are present.
• Type AC: Detects sinusoidal AC only. Not acceptable for circuits supplying EV chargers or solar inverters.
• Type F: Type A + smooth DC. Required by some EVSE manufacturers.
• Type B: Detects all types including smooth DC. Required for some three-phase EV chargers.

AFDD Requirements (Regulation 421.1.7 and Amendment 4 additions)

Arc Fault Detection Devices detect series and parallel arc faults — the type of fault that can cause fires in wiring without tripping overcurrent or RCD protection (e.g., damaged insulation that arcs but doesn't present as a full short circuit).

Mandatory scope (new in Amendment 4:2026): AFDD protection is now mandatory for socket-outlet final circuits rated up to 32A in Higher Risk Residential Buildings, Houses in Multiple Occupation (HMOs), purpose-built student accommodation, and care homes. This is a genuine "must fit" requirement in these premises types, not a recommendation.

Ordinary single-household domestic premises: Still recommended, not mandatory. Regulation 421.1.7 states AFDDs "should be considered" for domestic premises — particularly for circuits serving bedrooms and sleeping areas.

Best practice (and market direction):

• Install AFDD on all new or rewired domestic final circuits, even where not mandatory
• Minimum: bedroom circuits and circuits serving sleeping areas
• Combination RCBO+AFDD devices available from Hager, ABB, Siemens, Schneider
• Devices including RCCBs, RCBOs, circuit-breakers and AFDDs that are unidirectional now require directional marking (e.g. "line"/"load" or arrows) under Amendment 4

Note: Scotland has moved toward stronger AFDD requirements in new domestic builds ahead of the rest of the UK. Amendment 4's HMO/care home mandate for England and Wales may foreshadow a wider domestic mandate in a future amendment.

SPD Requirements (Regulation 443)

Regulation 443 requires a risk assessment to determine whether SPDs are needed. For domestic installations, the key question is: "Would loss of the installation or equipment have serious consequences?"

For most new domestic installations:

• Modern electronics (smart TVs, computers, routers, heat pump controllers) are highly susceptible to surge damage
• Risk assessment typically concludes SPD is warranted
• Type 1+2 SPD installed at the consumer unit; Type 2 is sufficient for most domestic
• Cost: ~£50–£150 for the device, plus installation time

EV Charging — Section 722 Requirements

Section 722 contains specific requirements for EV charging points:

Key requirements:

• Dedicated circuit from the consumer unit to the EVSE (no shared circuits)
• Socket-outlet type: unless protected by EVSE with BS EN 62955 (RCM), socket outlets must not be used for EV charging outdoors
• Protective earthing: TT installations require additional measures
• Type A RCD minimum; many wallbox manufacturers specify Type A or Type F
• Smart charging: EVSE must support OLEV (now OZEV) smart charging requirements for grant eligibility
• Load management: consider impact on existing supply capacity (single-phase 100A max; three-phase for high-demand installations)

Cable Selection and Sizing

Typical domestic circuit designs (Appendix 4, Table 4D2A — flat twin and earth):

Sizes assume clipped direct, no grouping, no thermal insulation. Always recalculate for actual installation conditions.

Periodic Inspection and EICR

EICR grading:

• C1 (Danger present): Immediate risk; rectify immediately; do not issue satisfactory certificate
• C2 (Potentially dangerous): Urgent remedial action required
• C3 (Improvement recommended): Not immediately dangerous but improvement advisable
• FI (Further investigation): Cannot determine condition without investigation

Mandatory EICR for rental properties (England):

• Every 5 years or on each new tenancy
• Landlord must provide tenant with copy within 28 days
• Remedial work (C1/C2) must be completed within 28 days (or sooner if urgent)
• Enforced by local authority (penalty up to £30,000)

Frequently Asked Questions

Do I need to use BS 7671 if I am not Part P registered?

Yes. BS 7671 applies to all electrical installations in the UK regardless of who carries them out. Non-compliance is not excused by not being Part P registered — it simply means the installation is both non-compliant with BS 7671 and unnotified under Building Regulations, which compounds liability.

What edition am I working to?

BS 7671:2018+A4:2026 (18th Edition + Amendment 4), published by the IET and BSI on 15 April 2026 and usable immediately for new work. The prior combination, BS 7671:2018+A2:2022+A3:2024, remains technically valid only until 15 October 2026 (a six-month transition window from publication of A4). After 15 October 2026, all new design work should be to +A4:2026. If you trained to the 17th Edition or an earlier 18th Edition amendment, you must have received update training — Amendment 4 introduces genuinely new mandatory requirements (domestic lighting-circuit RCD protection, AFDDs in HMOs/student accommodation/care homes), not just clarifications. Competent Person Schemes (NICEIC, NAPIT) require members to keep currency with amendments.

Is a Periodic Inspection the same as an EICR?

Yes — EICR (Electrical Installation Condition Report) is the formal name for what was previously called a Periodic Inspection and Test Report. The format changed with the 18th Edition.

Regulations & Standards

• BS 7671:2018+A4:2026 — Requirements for Electrical Installations (18th Edition + Amendment 4, current edition since 15 April 2026)

• Electricity at Work Regulations 1989 — Statutory duty to maintain electrical systems

• Building Regulations Part P — Electrical safety in dwellings

• Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020 — EICR requirements for landlords

• OZEV grant scheme — Electric Vehicle Homecharge Scheme requirements

• IET Wiring Regulations (BS 7671)

• IET: Amendment 4 (2026) to BS 7671:2018 press release

• NICEIC — Wiring Regulations guidance

• HSE — Electricity at Work Regulations

• part p overview — Part P notification requirements

• solar battery systems — Solar PV and battery requirements under BS 7671

• smart home systems — Smart home wiring considerations

• consumer unit replacement — Consumer unit replacement requirements