Motor running current calculator
Estimate single-phase or balanced three-phase AC running current from shaft kW, voltage, efficiency and power factor.
Result
Inputs used
- Motor shaft output (kW)
- 15
- Supply voltage (V; line-to-line for 3-phase)
- 400
- Power factor (0–1)
- 0.85
- Motor efficiency (%)
- 90
- AC supply
- Balanced three-phase
| Estimated electrical input | 16.666667 kW |
|---|---|
| Estimated running current | 28.301484 A |
Steady-state sinusoidal AC estimate at the entered operating point. Not a starting-current, VFD-input, cable-sizing or protective-device calculation. Confirm the nameplate and manufacturer data.
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Formula and worked example
Electrical input kW = shaft output kW / efficiency. For balanced three-phase AC, line current = input kW × 1,000 / (√3 × line-to-line voltage × power factor). For single-phase AC, omit √3.
A 15 kW shaft output at 90% efficiency needs 16.6667 kW input. At 400 V line-to-line and power factor 0.85, the estimated three-phase running current is 28.3015 A. Efficiency and power factor must describe the same operating point.
Use the right boundary
This steady-state estimate does not calculate locked-rotor current, acceleration, harmonic current, VFD line-side behavior, overload settings or cable ampacity. Use manufacturer data and applicable design requirements for equipment selection. The energy calculator can use the estimated electrical kW for an initial energy budget.
Frequently asked questions
Is efficiency the same as power factor?
No. Efficiency relates shaft power to real electrical input. Power factor relates real input power to apparent power. Both affect the running-current estimate.
Which voltage belongs in the three-phase formula?
Use line-to-line voltage, not line-to-neutral voltage. The model assumes a balanced supply and sinusoidal steady-state quantities.
Reference
U.S. Department of Energy: determining motor load and efficiency provides background on motor input, efficiency and power factor.
Go deeper
Cite this page: Motor running current calculator
, Shopfloor. https://shopfloor.space/tools/motor-current-calculator/