How it works
In a three-phase system use the line voltage (e.g. 400 V) and line current; in a single-phase system use the phase voltage (e.g. 230 V). Power factor accounts for the phase shift between voltage and current: 1 for resistive loads, typically 0.8–0.9 for motors.
Formula
1~: P = U · I · cos φ 3~: P = √3 · U · I · cos φ S = P / cos φ Q = √(S² − P²) Pshaft = P · η
The rating on a motor nameplate is the mechanical output at the shaft, so it equals the electrical input multiplied by the efficiency.
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