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How this is calculated#

The tool works out the full load current of a load. It uses the power, the voltage, the power factor and the efficiency. It works on one phase or three. It reads no table, so it cites no clause.

1. Supply. You pick one phase or three and enter the voltage. The voltage you enter sets the divisor in the last step.
2. Output power. You enter the load in kW or kVA. For a kW load, the tool takes this as the output power.
3. Apparent power drawn. It divides the output power by the efficiency and by the power factor. A kVA entry skips the power factor step.
4. Full load current. On one phase, it divides the apparent power by the voltage. On three phases, it divides by the voltage and by the square root of three.

On three phases, enter the line voltage, such as 400 V. On one phase, enter the phase voltage, such as 230 V.

Worked example#

• A 15 kW three‑phase load at 400 V. The power factor is 0.9 and the efficiency is 1. The apparent power drawn is 16.67 kVA. The full load current is 24.06 A.

Limits#

The result is the steady running current. It is not the starting current. A motor draws more current at start. Use the motor tool for the starting current.

The tool assumes a balanced load on three phases. It does not add a margin for the cable or the breaker. Size the cable from the design current with the cable size calculator. The tool gives no harmonic or neutral current.

Efficiency is a value between 0 and 1. A kVA entry is already an apparent power, so the tool does not divide it by the power factor.

Check the efficiency you enter. A motor rating in kW is a shaft output, so enter the motor efficiency. A resistive heater has an efficiency of 1. Check the power factor on the nameplate. A low power factor raises the current for the same kW.

See also: Commercial kitchen kW to amps, Three‑phase power kVA to amps at 400 V and the three‑phase power tool.