Motor full-load current workflow

How to prepare motor kW, voltage, phase, power factor and efficiency inputs before using the Australian full-load current calculator.

Current-estimate purpose

Motor full-load current estimates help turn kW, voltage, phase, power factor and efficiency into a current value for early worksheet review. The result is useful when a nameplate is missing, when a schedule needs a transparent assumption or when starting-current calculations need a documented input.

The estimate should not replace the motor nameplate, product data, protection study or installation design.

Workflow

  1. Confirm whether the motor record has nameplate current. If yes, keep it as the stronger field.
  2. Record rated kW, voltage, phase, power factor and efficiency assumptions.
  3. Use the motor full-load current calculator to calculate the estimate.
  4. Compare the estimate with nameplate current when available.
  5. Carry the documented current into starting-current, voltage-dip or protection review only with its source attached.

Input record

Motor full-load current record
FieldRecordWhy it matters
Motor powerkW or output rating from the project recordDrives the current estimate
Voltage basisEntered line or phase voltage as required by the calculatorCurrent changes with voltage
PhaseSingle-phase or three-phaseFormula path changes
Power factorEntered PF or documented assumptionLinks kW and kVA
EfficiencyEntered efficiency or documented assumptionSeparates output power from input power
Nameplate currentActual value where availableStronger than a formula estimate

Boundaries

  • Do not treat an estimated current as nameplate current.
  • Do not reuse PF or efficiency from another motor without labelling it as an assumption.
  • Do not use the current estimate alone to select protection or cable.
  • Do not hide whether the value came from calculation, nameplate, schedule or measurement.

Questions

Is calculated full-load current the same as nameplate current?

No. It is a worksheet estimate from entered assumptions. Use the nameplate where it is available and relevant to the motor being reviewed.

Which voltage should I enter for a three-phase motor?

Use the line voltage basis that matches the calculator field and the motor record, commonly 400 V in Australian three-phase planning unless the project documents say otherwise.