BS 7671 Cable Sizing Summary Guide (PDF)

BS 7671:2018+A2 (the IET Wiring Regulations, 18th Edition with Amendment 2) is the definitive wiring standard for the UK and many international markets. This 2-page A4 landscape summary covers the cable sizing workflow: determine design current Ib, select protective device rating In (In ≥ Ib), identify reference installation method (Table 4A2), apply correction factors for ambient temperature (Table 4B1) and grouping (Table 4C1), calculate required cable capacity It ≥ In / (Ca × Cg × Ci × Cc), select cable from current rating tables (Table 4D2A for XLPE), verify voltage drop per Appendix 12, and confirm earth fault loop impedance per Chapter 41. Exact clause references throughout.