How the values are calculated
Three-phase: I = S × 1000 / (√3 × V_LL)
Single-phase: I = S × 1000 / V
S in kVA, V in volts, I in amperes, √3 = 1.73205
The three-phase values assume a balanced load and use the line-to-line voltage. The single-phase column uses the voltage across the load, here 230 V. Power factor does not enter, because a kVA rating already includes it; to start from kW, divide by the power factor first (kVA = kW / PF).
Worked example
A 500 kVA transformer or generator on a 400 V three-phase system:
I = 500 × 1000 / (1.73205 × 400)
I = 500 000 / 692.82 = 721.7 A
At 415 V the same rating carries 695.6 A: the current falls in the ratio 400 / 415 because the same power is delivered at a higher voltage. A 10 kVA single-phase unit at 230 V carries 10 000 / 230 = 43.48 A.
Notes and limits
- These are currents at rated output. The current in service depends on the actual load; use the transformer loading or line current calculator for a measured or planned load.
- Large ratings are normally three-phase. The single-phase figures for the bigger sizes are shown only because the arithmetic is the same.
- For motors, the kVA drawn depends on efficiency and power factor, so read the nameplate current or use the motor current converter instead of this chart.
- Harmonic currents from electronic loads add to the RMS current; cables and transformers feeding such loads may need a margin beyond these values.