Motor full load current calculator
Enter the motor’s rated output, supply voltage, power factor and efficiency for its full load current, input power and indicative starting currents, then size the feeder cable with the voltage drop calculator.
Basis
I = P / (√3 × V × cos φ × η) for three-phase motors (V × cos φ × η for single-phase). Starting currents are indicative multiples.
Reference values for planning and comparison. Confirm against the current standard, the purchaser’s specification and the manufacturer’s datasheet before ordering.
Motor full load current at 415 V (0.85 PF, 90 % efficiency assumed)
| Rating | HP | Amps |
|---|---|---|
| 0.37 kW | 0.496 | 0.673 |
| 0.75 kW | 1 | 1.4 |
| 1.1 kW | 1.5 | 2 |
| 1.5 kW | 2 | 2.7 |
| 2.2 kW | 2.9 | 4 |
| 3.7 kW | 5 | 6.7 |
| 5.5 kW | 7.4 | 10 |
| 7.5 kW | 10.1 | 13.6 |
| 11 kW | 14.7 | 20 |
| 15 kW | 20.1 | 27.3 |
| 18.5 kW | 24.8 | 33.6 |
| 22 kW | 29.5 | 40 |
| 30 kW | 40.2 | 54.6 |
| 37 kW | 49.6 | 67.3 |
| 45 kW | 60.3 | 81.8 |
| 55 kW | 73.7 | 100 |
| 75 kW | 100.5 | 136.4 |
| 90 kW | 120.6 | 163.7 |
| 110 kW | 147.5 | 200 |
| 132 kW | 176.9 | 240.1 |
| 160 kW | 214.5 | 291 |
| 200 kW | 268.1 | 363.7 |
| 250 kW | 335.1 | 454.6 |
Worked example: 37 kW motor at 415 V
- Input power = 37 ÷ 0.93 = 39.8 kW.
- I = 39,785 ÷ (√3 × 415 × 0.86) = 64.4 A.
- Direct-on-line starting is roughly six times that, about 386 A: size the feeder and protection accordingly.
What is the full load current of a 15 kW motor?
At 415 V with 0.85 power factor and 90 % efficiency, about 27.3 A. The rating plate value is the one to design to.
Why is motor current higher than kW alone suggests?
A motor’s rated kW is shaft output. Input power is higher by the efficiency, and the current is higher again by the power factor.
How much current does a motor draw when starting?
Direct-on-line starting typically draws around six to seven times full load current; star-delta starting reduces it to roughly a third of that.