He turned to Table 4Ab. For 16mm² cable, volt drop was 2.8 mV/A/m. Run length: 35 meters. [ Vd = (2.8 \times 48 \times 35) / 1000 = 4.7 \text{ volts} ] Max allowed? 5% of 230V = 11.5V. He was safe. But if he’d used 10mm²? 4.4 mV/A/m would give 7.4V – still legal, but pushing it under full load.
He signed the certificate. His name. His liability. His peace of mind. cable calculations bs7671
The client, Mr. Ashworth, wanted a 7.4 kW car charger, a mini workshop, and LED spotlights. “Just wire it in,” he’d said. “My mate Dave says 2.5mm cable is fine.” He turned to Table 4Ab