BS 7671 explained: the UK wiring regulations for homes (18th Edition, A4:2026)

What is BS 7671 and where does it apply?

BS 7671, “Requirements for Electrical Installations”, is published jointly by the IET and BSI. It is a British Standard, not a law, but it is the recognised way to meet the legal requirements: the Electricity at Work Regulations, Part P of the Building Regulations in England and Wales, the Scottish Building Standards and the electrical safety rules for rented homes all point to it. Every competent-person scheme (NICEIC, NAPIT, ELECSA…) assesses its members against it.

The 18th Edition was published in 2018. Its amendments are consolidated: Amendment 4:2026 (published 15 April 2026 and usable immediately) replaces A2:2022 and A3:2024, and the previous consolidated text is withdrawn on 15 October 2026. A4 adds, among other things, stationary batteries (Chapter 57), functional earthing for ICT (section 545), Power over Ethernet (section 716), recognises Protective Neutral Bonding (PNB) and changes how EICR observations are coded. Rumours aside, no 19th Edition has been announced for publication.

Supply and earthing: what the design starts from

A British home is normally supplied at 230 V single-phase (tolerance +10 % / −6 %, ESQCR regulation 27) through a DNO cut-out fuse of up to 100 A. Most new supplies are TN-C-S (PME); older ones are often TN-S (earth from the cable sheath) and rural overhead supplies are TT (earth electrode). The designer uses the maximum external earth fault loop impedance (Ze) the DNO declares, and a prospective fault current of 16 kA for a single-phase supply up to 100 A.

Automatic disconnection is then checked circuit by circuit against the maximum earth fault loop impedance (Zs) of the protective device. For type B circuit breakers and 0.4 s (Table 41.3), the limits are 7.28 Ω for a B6, 2.73 Ω for a B16, 2.19 Ω for a B20 and 1.37 Ω for a B32; values measured at room temperature should stay around 80 % of these.

Socket circuits: rings, radials and floor area

The feature that sets the UK apart is the ring final circuit: both ends of the cable return to the same 32 A breaker, so each socket is fed from two directions. BS 7671 Appendix 15 and the IET On-Site Guide give three standard socket circuits for BS 1363 (13 A fused plug) sockets. They are limited by the floor area served, and the number of sockets is unlimited as long as the expected demand stays within the rating.

• Plan at least two socket circuits in a house (typically one per floor) and consider a separate circuit for the kitchen.
• A spur is a branch off a ring. An unfused spur may feed one single or one twin socket (or one fixed appliance); more than that needs a fused connection unit (FCU, 13 A BS 1362 fuse).
• Never on a ring: immersion heaters and storage heaters. Cookers and hobs above 2 kW get their own circuit.
• The 2.5 mm² ring is only acceptable in installation methods where the cable is not buried in thermal insulation (reference methods 100, 102, A or C).

Lighting, cooker, immersion heater, shower and EV circuits

Outside socket circuits, BS 7671 gives principles (Ib ≤ In ≤ Iz, voltage drop, disconnection times) rather than a fixed table. The values below are the usual domestic choices, which the Circuia UK pack also uses as defaults. Always check the cable length, the installation method and the manufacturer's instructions.

RCDs, AFDDs and surge protection

Additional protection by a 30 mA RCD is required for socket-outlets up to 32 A (411.3.3), for lighting circuits in dwellings (411.3.4), for cables concealed less than 50 mm deep in walls or partitions without mechanical protection (522.6.202/203), for every circuit of a room containing a bath or shower (701.411.3.3) and for each EV charging point (722). In practice, every final circuit of a new home ends up protected.

• No maximum number of circuits per RCD is fixed by the standard, but the installation must be divided to limit nuisance tripping. Two common boards: dual RCD (split load, circuits shared between two 30 mA RCDs) or full RCBO (one RCBO per circuit), now the usual choice.
• Type A RCDs are the practical default; type AC is limited to equipment without DC components.
• AFDDs (arc fault detection, BS EN 62606, 421.1.7) are required on socket circuits up to 32 A in higher-risk residential buildings, HMOs, purpose-built student accommodation and care homes, and recommended everywhere else.
• Surge protection (SPD): since A2:2022 the risk calculation and the single-dwelling exemption are gone. A type 2 SPD is installed unless the owner explicitly declines it where the risk is only to equipment.

Bathrooms and shower rooms (Section 701)

Rooms containing a bath or shower have zones 0, 1 and 2 (zone 3 was removed in 2008). Zone 1 rises to 2.25 m above the floor (or the highest fixed shower outlet) above the bath or tray; without a tray it extends 1.2 m from the centre of the fixed water outlet. Zone 2 extends 0.6 m beyond zone 1.

Adding or altering anything within a bath or shower special location is notifiable work in England (and all bathroom work is notifiable in Wales).

EV charge points (Section 722)

• Each charge point has its own final circuit and its own 30 mA RCD: type B, or type A/F with 6 mA DC detection (RDC-DD, usually built into the charger).
• On a PME (TN-C-S) supply, a charge point that can serve a vehicle outdoors may not simply use the PME earth (722.411.4.1). The usual solution is an open-PEN device that disconnects all live conductors and the protective conductor within 5 s when the voltage leaves 207–253 V, or a TT earth electrode.
• DNO notification: under the ENA connect and notify process, a charger or heat pump can be installed and then notified within 28 days when the home's maximum demand stays within 60 A per phase; otherwise apply first.
• Chargers sold since 30 June 2022 must meet the Electric Vehicles (Smart Charge Points) Regulations 2021 (smart functions, default off-peak charging, randomised delay).

Consumer unit, heights and Scottish minimums

Since 2016, consumer units in domestic premises (garages and outbuildings included) must comply with BS EN 61439-3 and have a non-combustible enclosure, typically steel (421.1.201). In new dwellings in England, Approved Document P (through Part M) places the consumer-unit switches at 1350–1450 mm and sockets and switches between 450 and 1200 mm above the finished floor.

England, Wales and Northern Ireland set no minimum number of sockets or lighting points. Scotland does, for work under a building warrant:

Certificates, Part P and inspection

1. Registered competent person (NICEIC, NAPIT, ELECSA, Stroma…): the installer self-certifies and notifies; the usual route.
2. Registered third-party certifier: inspects and tests work done by someone who is not registered.
3. Building control body: notified before work starts, then inspects.

Private landlords in England must have an EICR at least every five years and fix C1/C2 defects within 28 days; Northern Ireland and Scotland have similar five-year rules.

Designing a BS 7671 installation with Circuia

Choose United Kingdom when you create the project (and England, Wales, Scotland or Northern Ireland as the nation). The editor then wires sockets as 32 A rings up to 100 m² or area-limited radials, adds spurs and FCUs, proposes one type A RCBO per circuit, sizes the lighting, cooker, immersion and EV circuits with the values above, checks the bathroom distances and, for Scotland, the Standard 4.6 minimums. The single-line diagram, board schedule and bill of materials follow.

Open the editor set up for the United Kingdom — free, in your browser.

Common mistakes

• ×Counting sockets per circuit instead of checking the floor area a ring or radial serves.
• ×Putting an immersion heater or storage heaters on the ring.
• ×Fitting a 230 V socket closer than 2.5 m to zone 1 of a bathroom.
• ×Leaving lighting circuits without RCD protection in a new home (required since 2018).
• ×Installing a plastic consumer unit in a house or garage.
• ×Using the PME earth for an outdoor EV charge point without open-PEN protection.

Frequently asked questions

Related pages

• OverviewElectrical wiring standards in Europe, country by countryHome wiring rules explained for the UK (BS 7671), Ireland (I.S. 10101), Norway, Sweden, Denmark and Finland, with the Circuia editor for each country.
• CircuiaPricing: free, Project Pass €39, Pro €49/monthCircuia plans: Free to explore, Project Pass at €39 incl. VAT for a homeowner project, Pro at €49 excl. VAT/month and Team at €129 excl. VAT/month for electricians. 14-day trial.
• CircuiaCircuia: AI wiring plans to BS 7671 and EU standardsDraw your home or ask the AI: Circuia designs circuits and the consumer unit, checked against BS 7671, I.S. 10101 and the rules of 17 European countries.