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.
He signed the certificate. His name. His liability. His peace of mind. cable calculations bs7671
That evening, Tom sat in his van again. He’d run the cables, drilled the holes, and tested everything – continuity, insulation resistance, RCD trip times. All passed. He flipped open the regs to Section 433
At 9 a.m., he knocked on Ashworth’s door. “What’s the damage?” the client asked. “More than Dave’s quote,” Tom said, showing the scribbled page of calculations. “But Dave’s house hasn’t burned down yet. That’s just luck, not engineering.” He signed the certificate
He circled the final design: 16mm² twin and earth. 50A Type C RCBO. Earthing via TN-C-S, but only after verifying the DNO’s maximum Ze.
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.