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Three-Phase Motor Power & %FLA

Clamp the leads, read the voltage, and find out whether that motor is actually loaded — input kW and kVA, an estimate of shaft horsepower, and the reading as a percentage of nameplate FLA.

Free tool · BAS Field Fundamentals

Works offline. Every calculation runs on your device, no signal needed. Install the BAS Field Reference app to keep it on your phone.

How to use it

  1. Measure line-to-line voltage at the motor and clamp each leg; enter the average current.
  2. Use the drive's reported power factor if you have it. Across-the-line motors at full load sit around 0.85–0.90; lightly loaded, much lower.
  3. Compare the % of nameplate FLA to what the sequence says the motor should be doing. A fan commanded to full speed pulling 60% FLA is not moving design air.
  4. On a VFD, current — not voltage — tracks load. A drive holds volts-per-hertz roughly constant, so a half-speed motor still sees near-nameplate voltage while its amps drop.

Practice reading amps against nameplate in the simulator →

Voltage present does not mean the circuit can do work. A motor can sit at 480 V on all three legs and draw almost nothing because it is uncoupled, the load is gone, or a belt is off. The clamp tells you what the voltmeter can't.

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More where this came from

This calculator comes out of BAS Field Fundamentals — electrical fundamentals for BAS work, how to prove a motor is loaded, and the failure modes that produce a confident, wrong diagnosis. Plus 20 field cases and a browser simulator to practice on.

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