Calculate amps per phase for a three-phase load from kW and line voltage with a typical 0.8 power factor, or solve for power, voltage or power factor.

0.8 is the standard rating basis for motors and generators; use 1 for resistive loads such as heaters, or your measured PF.

Output units and connection details

Amps Per Phase Formula

The formula estimates RMS line current in each conductor of a balanced three-phase load, using total real input power and RMS line-to-line voltage.

APP = P × 1000 / √(3) × V × PF

Variables:

  • APP is RMS line current in each supply conductor (A), not delta winding current
  • P is total three-phase real electrical input power (kW)
  • V is RMS line-to-line voltage (V)
  • PF is power factor at the operating load (unitless; positive for this inverse formula)

To calculate the amps per phase, multiply the power by 1000 to convert it to watts, then divide by the product of the square root of 3, the voltage, and the power factor.

What is Amps Per Phase?

Here “amps per phase” means line current, not the sum of the three conductor currents. For balanced sinusoidal wye, branch current equals line current and branch voltage equals line-to-line voltage / √3. For balanced delta, branch voltage equals line-to-line voltage and branch current equals line current / √3. PF is real power / apparent power (cosine of the voltage-current phase angle for sinusoidal conditions). This calculation does not verify safe conductor ratings, startup behavior or an unbalanced system.

How to Calculate Amps Per Phase?

The following steps outline how to calculate the Amps Per Phase.

  1. First, determine total three-phase real input power (P) in kilowatts (kW), not per-phase power or motor shaft output.
  2. Next, determine RMS line-to-line voltage (V) in volts.
  3. Next, use PF at the operating load. It must be greater than 0 and at most 1 to solve line current or voltage. Forward real-power mode permits PF = 0; PF cannot be inferred if apparent power is zero.
  4. Next, gather the formula from above = APP = (P * 1000) / (√3 * V * PF).
  5. Finally, calculate the Amps Per Phase (APP) in amperes (A).
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Power (P) = 50 kW

Voltage (V) = 400 V

Power Factor (PF) = 0.8. Thus Iline = 50000 / (√3 ×400 ×0.8) ≈90.21098 A. Each phase has 16.666667 kW real power. Wye branch voltage is approximately 230.940108 V with 90.21098 A branch current; delta branch voltage is 400 V with 52.083333 A branch current.