Calculate motor full-load current from its rating, voltage, efficiency and power factor.
Full-load current follows from the shaft rating once efficiency and power factor are accounted for. Cables are sized above this figure and overload relays set just above it to protect the winding without nuisance tripping. A 15 kW motor at 400 V draws around 27 A, and this is the starting point for every cable, contactor and protection selection.
Motor Current
I = P ÷ (√3 V η cos φ) for three phase
I = P ÷ (√3 V η cos φ) for three phase Full-load current follows from the shaft rating once efficiency and power factor are accounted for. Cables are sized above this figure and overload relays set just above it to protect the winding without nuisance tripping.
A 15 kW motor at 400 V draws around 27 A, and this is the starting point for every cable, contactor and protection selection.
This calculator takes 5 inputs: Motor rating, Supply voltage, Motor efficiency, Power factor, Phases. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.