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How to Convert 3 Phase Wattage to Amps

Correctly calculating power consumption facilitates accurate cost analysis and also determines how much work a device is doing. Three-phase power calculations is not much more complicated than calculating single-phase power, but the Voltages and currents on the three supply lines often have different values. Measuring the voltage and current on each line and taking the averages of these values makes the calculation more accurate. Including the power factor in the calculation also increases the accuracy of the result.

Things You'll Need

Multimeter with clamp on ammeter.
Calculator with square root function

Instructions

- 1
  Operate the equipment at full speed and under full load conditions. Measure the phase-to-phase voltage across each pair of lines. There are three supply lines in three-phase current, often labeled L1, L2 and L3. Measure the voltage across the L1 and L2, L2 and L3, and L1 and L3 terminals. Record each voltage measurement.
- 2
  Open the ammeter clamp and place it around the L1 wire. Record the current reading. Open the clamp, remove it from L1 and place it on L2. Record the reading and repeat the process for L3.
- 3
  Add the three voltages together and divide the result by three. The result is the average voltage. Add the three current readings together and divide by three. The result is the average current reading.
- 4
  Multiply the average voltage by the average current, then multiply the result by the square root of three. This provides the number of volt-amps used by the device under the load conditions it was tested under.
- 5
  Multiply volt-amps by the power factor of the device if it is known. Unless a load is purely resistive, such as an incandescent light or electric heater, the power factor is less than 1.0. If the power factor is unknown, many engineers and electricians use 0.80 as the power factor. The result is in watts.

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