3-Phase Motor Amperage Calculator — Full-Load Current
Enter the motor nameplate data — rated shaft power (kW), supply line voltage, power factor and efficiency — and instantly find the full-load line current, apparent power (kVA), reactive power (kVAR) and motor losses.
kW
V
Full-load line current drawn by the motor from each phase
- 1
Shaft power in watts
10 kW × 1000 = 10,000 W - 2
Electrical input power
10,000 W ÷ 0.9 = 11,111.11 WDividing by efficiency accounts for heat and mechanical losses inside the motor. - 3
Line current
11,111.11 ÷ (√3 × 400 × 0.85) = 18.87
How does this calculator work?
Three-phase motor line current: I = P_shaft / (√3 × V_L × PF × η). Enter rated shaft kW, line voltage, power factor and efficiency to get full-load amps, apparent power (kVA) and reactive power (kVAR). Use 125 % of the result for cable and breaker sizing.
Formula
How this is calculated
A three-phase AC induction motor draws electrical power from three phases simultaneously. For a balanced supply the full-load line current is I = P_electrical / (√3 × V_L × PF), where V_L is the line-to-line voltage, PF is the power factor (cos φ), and P_electrical is the active electrical input power. Because the motor is not 100 % efficient, the input power exceeds the nameplate shaft output: P_electrical = P_shaft / η. Combining both gives: I = P_shaft / (√3 × V_L × PF × η).
Apparent power S (kVA) is the product √3 × V_L × I and represents the total complex power the supply must deliver. Reactive power Q (kVAR) = S × sin(arccos(PF)) is the non-working component stored and released by motor windings each cycle — it does not appear on your electricity bill but forces larger cable and transformer sizing.
The power factor and efficiency figures shown are editable estimates; always use the motor nameplate or manufacturer datasheet for accurate sizing. Typical IE3-class motors have η ≈ 0.88–0.95 and PF ≈ 0.80–0.92 at full load. The formula assumes a balanced, sinusoidal supply — voltage unbalance or harmonics will increase the actual current.
Frequently asked questions
Power factor accounts for the reactive current the motor magnetism needs (which does not do shaft work), while efficiency accounts for thermal and mechanical losses inside the motor. Both reduce the electrical-to-mechanical conversion, so both must be included to find the actual line current drawn.
Enter the line-to-line (phase-to-phase) voltage — typically 400 V in Europe, 415 V in Australia/India, or 480 V in North America. The formula already divides by √3 internally, so do not use the phase voltage (230 V / 277 V).
Apply a safety margin: cables are typically sized for 125 % of full-load current and circuit breakers for 115–125 % (per IEC 60364 / NEC 430). Also check the motor's locked-rotor current (usually 6–8× FLA) to verify the breaker trip curve survives start-up.
Also known as
TG we-Calculate Editorial Team. (2026). 3-Phase Motor Amperage Calculator — Full-Load Current [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/3-phase-motor-amperage-calculator
TG we-Calculate Editorial Team. "3-Phase Motor Amperage Calculator — Full-Load Current." TG we-Calculate. 2026. https://we-calculate.com/calculator/3-phase-motor-amperage-calculator.
TG we-Calculate Editorial Team, "3-Phase Motor Amperage Calculator — Full-Load Current," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/3-phase-motor-amperage-calculator
@misc{wecalculate_3_phase_motor_amperage_calculator, title = {3-Phase Motor Amperage Calculator — Full-Load Current}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/3-phase-motor-amperage-calculator}}, year = {2026}, note = {TG we-Calculate} }
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