How this calculator works
Power divided by voltage gives DC current. In AC systems, power factor accounts for the part of apparent power that becomes real power. Balanced three-phase line current uses a different multiplier depending on whether voltage is measured between lines or from line to neutral. For motors, enter electrical input watts rather than mechanical shaft output unless efficiency has already been applied.
Formula
I = P/(k V PF); k = 1 for DC or single phase, sqrt(3) for three-phase line-to-line, and 3 for three-phase line-to-neutral; PF = 1 for DC.
Worked example
A 1200 W DC load at 120 V draws 10 A. A balanced three-phase 2400 W load at 100 V line-to-neutral and power factor 0.8 also draws 10 A per line.
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Frequently asked questions
Can I enter output watts for a motor?
First divide mechanical output power by motor efficiency to obtain electrical input power.
Which voltage is used for three-phase?
Choose the selector matching your line-to-line or line-to-neutral RMS measurement.
What if I do not know power factor?
Use a measured or manufacturer-specified value. Assuming one can underestimate current.