Electrical figures, short of BS 7671
Three tools sit on the electrical side. Ohm’s law is a resistive relationship. The voltage-drop page is copper resistivity at about 20°C, go and return. Three-phase power is √3 × line voltage × line current × power factor.
Worked three-phase case
400 V, 32 A, power factor 0.85 is 18.85 kW and 22.17 kVA. That is the steady electrical load. It is not the cable size. Diversity, grouping, installation method, disconnection time and voltage drop from the appendix tables are a different calculation, in BS 7671, with the installation method known.
Use three-phase power and the voltage-drop estimate only as far as the label on the page.
Last checked 2 October 2026. Original guidance. Standards text stays with the publisher.