BS 7671 (UK)

BS 7671 — the IET Wiring Regulations — is the UK’s authoritative electrical installation standard. WireSketch implements the 18th edition with Amendment 2 (2022). Here’s what that covers and what it doesn’t.

What BS 7671 is

BS 7671 is published jointly by the IET (Institution of Engineering and Technology) and BSI. It’s the standard cited by Part P of the Building Regulations for England and Wales, by the equivalent Scottish and Northern Irish technical standards, and by every UK electrical certification scheme (NICEIC, NAPIT, ELECSA, Stroma).

It’s a thick book. The parts most relevant to residential planning:

• Part 1 — scope and definitions
• Chapter 41 — protection against electric shock (RCD types, disconnection times)
• Chapter 43 — overcurrent protection (RCBO, MCB ratings)
• Section 701 — rooms containing a bath or shower (zones, IP ratings)
• Section 522 — cable selection and erection (incl. the safe zones for buried cables)
• Appendix 15 — ring + radial final circuit conventions (the UK’s distinctive ring main approach)

Amendment 1 vs Amendment 2

The 18th edition was published in 2018. Amendment 1 (2020) reorganised Part 8 around energy efficiency and prosumer installations. Amendment 2 (2022) — the version most professional installers now work to — tightened:

• AFDD (Arc Fault Detection Device) requirements for higher-risk locations (HMOs, care homes, student accommodation)
• Surge protection devices — now mandatory in many residential installations unless a specific risk assessment exempts
• EV charging point installation rules (Section 722)
• RCD type requirements where the load contains DC components (EV chargers, solar inverters — Type A no longer always sufficient, Type B may be needed)

WireSketch’s BS 7671 defaults align with Amendment 2.

Where it applies

• England + Wales — cited by Part P of the Building Regulations.
• Scotland — recognised via the Scottish Technical Handbook.
• Northern Ireland — recognised via local building control.
• Republic of Ireland — uses its own national rules (ET 101/I.S. 10101) that share IEC roots with BS 7671 but diverge in detail. WireSketch’s BS 7671 selector is a rough approximation for Ireland, not a substitute for the Irish standard.

Key requirements

• Cable — Twin & Earth (T&E) for fixed wiring in residential; SY/SWA for outdoor and buried.
• Ring main — 32 A ring final circuit serving up to 100 m² floor area, protected by 32 A MCB/RCBO.
• Radial circuits — lighting (6 A or 10 A B-curve), dedicated appliance loads (cooker, immersion, EV charger).
• RCD protection — 30 mA on all socket-outlet circuits, all bathroom circuits, and all buried cables less than 50 mm deep.
• Bathroom zones — IEC 60364-7-701 model: Zone 0 inside the bath, Zone 1 above, Zone 2 to the side. No 13 A sockets in Zones 1 or 2 (shaver supply only).
• Earthing — TT, TN-S, or TN-C-S system depending on supply; main equipotential bonding to incoming water/gas services.

What WireSketch models from BS 7671

• Vertical and horizontal cable safe zones per Section 522
• Switch height (~120 cm) and socket height (~45 cm) defaults aligned with typical UK practice
• IEC 60364-7-701 Zone 0/1/2 in wet-room mode
• Twin & Earth cable type with appropriate cross-sections in cable recommendations
• 32 A RCBO + ring final circuit as the default for socket circuits in the panel template
• Type A RCD as default, with a note in the Knowledge Base entry that Type B may be required for EV charging or PV installations under Amendment 2

What WireSketch doesn’t model

• AFDD specific-location rules — the app doesn’t flag HMO/care-home/student-accommodation circuits that require AFDDs under Amendment 2.
• Surge protection device (SPD) selection — mandatory in many installations under A2 but not part of the panel template.
• Disconnection time calculations — required for Chapter 41 compliance, not modelled.
• Loop impedance and PSCC (prospective short-circuit current) values — site-measured during installation, not the planner’s scope.
• Ireland (ET 101 / I.S. 10101) deltas — the BS 7671 selector is an approximation; the Irish standard differs in detail.

Practical tip

For a UK homeowner planning a kitchen rewire: capture the layout in WireSketch, pick BS 7671 as the region, generate the Renovation Brief PDF, and hand it to a Part P-registered electrician. The electrician will translate your layout into a compliant design, perform the notifiable-work certification, and lodge the work with the relevant building control body. The brief saves them — and you — significant ambiguity in the quoting stage.