Single phase power calculator

Single-phase power is voltage times current times power factor. A 13 A load at 230 V with a power factor of 1 is 2,990 W — which is why a UK 13 A plug fuse is the practical ceiling for a domestic appliance at about 3 kW.

Single phase is what almost every home has, and its ceiling is lower than people expect. A 230 V circuit protected at 16 A tops out near 3.7 kW; a 120 V circuit at 15 A stops at 1.8 kW. That is why electric showers, hobs and car chargers need their own dedicated circuits rather than a socket, and why North American homes run high-power appliances from a 240 V split-phase circuit instead. Knowing the arithmetic makes the wiring conventions stop looking arbitrary.