How it's calculated

Three-phase: I = P ÷ (√3 × V × PF × η) Single-phase: I = P ÷ (V × PF × η) 1 hp = 745.7 W

Motor ratings are shaft output power, so efficiency (η) converts them back to the electrical input. Power factor and efficiency both fall at part load, and a lightly loaded motor often draws well below its full-load current.

Use the nameplate full-load current to set overloads whenever you have it. In the US, the NEC requires table values (430.248/430.250), not calculated current, for sizing conductors and short-circuit protection.

Typical values if the nameplate is missing

Motor size	Power factor	Efficiency
0.75–4 kW	0.75–0.84	78–88%
5.5–22 kW	0.82–0.87	88–93%
30–110 kW	0.85–0.90	93–96%

These are rough ranges for 4-pole IE2/IE3 motors.