Cable Calculations Bs7671 Page

Tom snorted. Dave wasn’t here. Dave didn’t have to sign the Electrical Installation Certificate. Dave wouldn’t get sued if the cable melted and burned the house down.

He flipped open the regs to Section 433 – Protection against overcurrent . Then to Appendix 4, the cable rating tables. He grabbed his notepad, the one with coffee stains and a torn spine. cable calculations bs7671

Adiabatic equation. The one that stops you dying. [ S = \frac{\sqrt{I^2 \times t}}{k} ] He measured the earth fault loop impedance (Zs) at the board: 0.35Ω. A 48A load meant a 230A fault current. The 32A Type B MCB would trip in 0.1 seconds. Copper k factor = 115. [ S = \frac{\sqrt{230^2 \times 0.1}}{115} = \frac{72.7}{115} = 0.63\text{mm}^2 ] His 16mm² earth was massively overkill. But if he’d used a cheap 1.5mm? Zap. No second chances. Tom snorted