kW to Amps Calculator

It depends on the supply. DC: amps = kW x 1,000 / volts. AC single-phase: amps = kW x 1,000 / (volts x PF). AC three-phase: amps = kW x 1,000 / (volts x PF x 1.732), using the 400 V line voltage. Power factor (PF) matters for AC because the current must cover reactive power too: at PF 0.8 a load draws 25 percent more current than the kW alone suggests.

On a 230 V single-phase supply at unity power factor, 7,400 / 230 = 32.2 A, which is why 7.4 kW chargers are installed on dedicated 32 A circuits. A 22 kW three-phase charger draws 22,000 / (400 x 1.732) = 31.8 A per phase, so it also sits on a 32 A way but needs all three phases. Always confirm spare capacity at the distribution board before adding chargers.

A three-phase supply delivers power across three conductors at a 400 V line voltage, so the work is shared. The same 22 kW load draws roughly 96 A on 230 V single-phase but under 32 A per phase on 400 V three-phase at unity power factor. Lower current means smaller cables, lower losses and less voltage drop, which is why motors and larger plant are almost always connected three-phase.

The nominal voltage is 230 V single-phase and 400 V three-phase, harmonised across Europe, with a permitted tolerance of +10 percent to -6 percent. In practice many UK sites measure nearer 240 V because the network was built to the older standard. For cable and breaker sizing, calculating at 230 V is the conservative convention, since lower voltage means higher current for the same kW.

Resistive loads such as heaters and immersion elements run at 1.0. Motors typically run between 0.8 and 0.9 under load, and lower when lightly loaded. EV chargers and modern IT power supplies operate close to unity. If you have half-hourly metering, divide recorded kW by recorded kVA for the true site figure. When in doubt, 0.9 is a reasonable commercial assumption that slightly overstates current.