18th Edition Wiring Regulations
Summary guide to BS 7671:2018+A2:2022
What is BS 7671?
BS 7671 is the national standard for electrical installations in the UK, commonly known as “the Wiring Regulations.” The 18th Edition (published 2018, current version with Amendment 2 from 2022) sets out the rules for the design, erection, and verification of electrical installations up to 1000V AC / 1500V DC. While not a statutory document itself, compliance with BS 7671 is regarded as meeting the requirements of the Electricity at Work Regulations 1989.
Amendment History
| Edition / Amendment | Date | Summary |
|---|---|---|
| BS 7671:2018 | July 2018 | 18th Edition published. Replaced 17th Edition (BS 7671:2008+A3:2015). |
| Amendment 1 (A1) | February 2020 | EV charging infrastructure updates and minor corrections. |
| Amendment 2 (A2) | March 2022 | AFDDs, SPDs redrafted, energy efficiency (Part 8), prosumer installations, metallic cable support. |
| Amendment 3 (A3) | 2024 | Prosumer installations refinement, bidirectional power flows. |
Key Changes from the 17th Edition
Arc Fault Detection (AFDDs)
Mandatory in HRRBs, HMOs, student accommodation, and care homes. Recommended for all other premises.
Surge Protection (SPDs)
Consequence-based approach. Required where overvoltage could cause serious injury, safety service failure, or significant financial loss.
RCD Protection — Expanded
30mA RCD for all socket-outlets up to 32A, mobile equipment up to 32A outdoors, and all lighting circuits in domestic premises.
Metallic Cable Support
All wiring must be supported by non-combustible metallic clips/saddles/ties. Plastic clips no longer acceptable as sole support.
Metal Consumer Units
Consumer units in domestic premises must be non-combustible material (metal enclosures).
Prosumer Installations
New requirements for installations that consume and produce electricity — solar PV, battery storage, EV V2G.
EV Charging
Updated requirements for EV charge points including PME earthing considerations and cable sizing.
Energy Efficiency
New part requiring designers to consider energy efficiency of the electrical installation.
AFDD Requirements by Building Type (Reg 421.1.7)
AFDDs detect low-level series and parallel arcs that MCBs and RCDs cannot. They analyse the electrical waveform and disconnect before localised heat causes fire.
| Building Type | Requirement | Note |
|---|---|---|
| Higher Risk Residential Buildings (HRRBs) | Mandatory | Socket-outlet circuits up to 32A |
| Houses in Multiple Occupation (HMOs) | Mandatory | Socket-outlet circuits up to 32A |
| Purpose-built student accommodation | Mandatory | Socket-outlet circuits up to 32A |
| Care homes | Mandatory | Socket-outlet circuits up to 32A |
| All other premises (standard homes, commercial) | Recommended | "Should" language — not mandatory |
SPD Requirements (Reg 443.4.1)
Amendment 2 replaced the complex “Calculated Risk Level” with a simpler consequence-based approach. SPDs must be provided where overvoltage could result in:
- • Serious injury to, or loss of, human life
- • Failure of a safety service (fire alarms, emergency lighting, medical equipment)
- • Significant financial or data loss
In all other cases, SPDs are required unless the owner explicitly declares acceptance of risk (advised in writing). In practice, since most homes have smoke alarms (a safety service), the opt-out is increasingly rare.
Structure of BS 7671
| Part | Title | Key Content |
|---|---|---|
| Part 1 | Scope, Object and Fundamental Principles | Sets out who and what the regs apply to. Chapter 13 covers fundamental principles. |
| Part 2 | Definitions | All defined terms — expanded for EV, prosumer, and energy storage terminology. |
| Part 3 | Assessment of General Characteristics | Supply assessment (voltage, frequency, current), earthing system (TN-S, TN-C-S, TT), external influences. |
| Part 4 | Protection for Safety | Technical core: shock protection, thermal effects, overcurrent, ADS disconnection times, AFDDs, SPDs. |
| Part 5 | Selection and Erection of Equipment | Cable selection, installation methods, earthing, isolation and switching, metallic support. |
| Part 6 | Inspection and Testing | Initial verification and periodic inspection. Skilled persons required. References GN3. |
| Part 7 | Special Installations and Locations | Bathrooms (701), swimming pools (702), construction sites (704), solar PV (712), EV (722). |
| Part 8 | Energy Efficiency (A2) | Chapter 82: Prosumer installations — direct feeding, island mode, and reverse feeding. |
Key Regulation Numbers
Regulation numbers every UK electrician should know.
| Reg. | Topic | Detail |
|---|---|---|
| 411.3.3 | Disconnection times | TN systems: 0.4s (230V). TT systems: 0.2s (230V). Ensures ADS operates fast enough for shock protection. |
| 411.3.4 | Additional RCD protection | 30mA RCD for socket-outlets ≤32A, mobile equipment outdoors, and all domestic lighting circuits. |
| 421.1.7 | AFDDs | Mandatory in HRRBs/HMOs/care homes. "Shall" = mandatory. "Should" = recommended. |
| 421.1.201 | Metal consumer units | Non-combustible enclosures in domestic premises. |
| 433.1 | Overload protection | Ib ≤ In ≤ Iz and I2 ≤ 1.45 × Iz. |
| 434 | Fault current protection | Verified using adiabatic equation: S = √(I²t) / k. |
| 443.4.1 | Surge protection | Consequence-based SPD requirements. Required unless owner accepts risk in writing. |
| 514.14.1 | Wiring colours | Non-harmonised colours require a permanent warning notice at the distribution board. |
| 521.10.202 | Metallic cable support | Non-combustible metallic fixings for all wiring systems. |
| 525 | Voltage drop | Max 3% for lighting, 5% for other loads (between origin and load terminals). |
| 543 | Protective conductors | CPC sizing: S ≤ 16mm² → same as line; 16–35mm² → 16mm²; >35mm² → S/2. |
| 701 | Bathrooms | Zone requirements and minimum IP ratings for bathroom locations. |
| 722 | EV charging | Supply, earthing (PME considerations), and cable requirements for EV charge points. |
Understanding BS 7671 Language
“shall”
Mandatory requirement. Must be complied with.
“should”
Recommended. Best practice but not mandatory.
“may”
Permission. An acceptable option if chosen.
Building Regulations by Region
| Region | Regulation | Key Detail |
|---|---|---|
| England & Wales | Part P Building Regulations | Notifiable work must be done by Competent Person Scheme member (NICEIC, NAPIT, ELECSA) or notified to building control. |
| Scotland | Building Standards 4.5 & 4.6 | Standards for electrical safety; references BS 7671. Building warrant may be required. |
| Northern Ireland | Technical Booklet E + Electrical Safety Standards | Landlords must meet 18th Edition. 5-year inspection cycle for rental properties. |
Who Must Comply?
- • All new electrical installations in the UK
- • Additions and alterations to existing installations
- • Part P notifiable work in domestic premises (England & Wales)
- • Required by the Electricity at Work Regulations 1989 and Building Regulations
- • Competent person schemes (NICEIC, NAPIT, ELECSA) audit against BS 7671
- • Existing installations are assessed against the edition current at the time of installation during EICRs — missing AFDDs on an old installation is typically C3 (satisfactory), not C2