UK Standard

BS 7671 — IET Wiring Regulations

BS 7671 — Requirements for Electrical Installations (IET Wiring Regulations)

In short: BS 7671 (IET Wiring Regs) sets UK rules for selecting domestic electrical cable sizes based on current, installation method, and run length.

What BS 7671 covers

Cable sizing must satisfy current-carrying capacity, voltage drop and protection requirements under BS 7671; undersized cable is a fire and safety risk.

The standard accounts for installation method and grouping (de-rating factors) as well as the load, which is why a longer run may need a larger cross-section.

Apply this standard

Calculators that use BS 7671

Electrical Cable Size Calculator

Minimum cable cross-section for safe power delivery over any run length.

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Official source: IET — BS 7671 Wiring Regulations. Figures on this page are a plain-English summary for estimating purposes — always refer to the published standard for compliance.