Power Calculations, Solved
The tools an electrician or controls tech reaches for when working with three-phase systems. Quick conversions, imbalance checks, capacitor sizing, and phase identification.
Three-Phase Power and Current
Enter line voltage, real power, and power factor to get the line current, apparent power, and reactive power for a balanced three-phase load.
The three-phase line current fits inside the limit you entered with reasonable headroom. Always confirm conductor ampacity and breaker sizing against NEC 430 for the final install.
Assumes a balanced three-phase load. Enter a breaker or service limit to check the current against it. For the final install, size conductors and overcurrent devices per NEC 430.
Wye vs Delta Converter
Pick the connection, tell it whether you know the phase or line values, and get the matching line and phase voltage and current.
In a wye connection the line voltage is the square root of three (about 1.732) times the phase voltage, while line and phase current are equal. That is why a 277 volt phase gives a 480 volt line, and 120 volt gives 208 volt.
Voltage Imbalance Checker
Enter the three line-to-line voltages to get the NEMA percent unbalance and the motor derate it calls for.
Voltage imbalance is at or below 1 percent, the NEMA action threshold. No motor derate is required. Keep an eye on it, since a small imbalance still drives a larger current imbalance.
Percent unbalance is the largest deviation of any reading from the three-phase average, divided by that average. NEMA acts above 1 percent, and a small voltage unbalance drives a current unbalance several times larger that overheats one winding.
Power Factor Correction Sizer
Enter the load and the present and target power factor to size the three-phase capacitor kVAR needed.
This kVAR moves the load from the present to the target power factor and frees up feeder and transformer capacity. Switch the bank in steps and confirm it does not lead under light load.
Correcting power factor lowers the reactive current, frees up feeder and transformer capacity, and avoids utility penalties. Switch large banks in steps and confirm the load does not go leading under light demand.
Two-Wattmeter Power Reader
Enter the two wattmeter readings to get total three-phase power and the power factor, with the sign rule applied for you.
Both wattmeters read positive, so the power factor is above 0.5. Total three-phase power is the sum of the two readings, and the ratio between them sets the exact angle.
In the two-wattmeter method the total power is always the sum of both readings, even when one is negative. Both positive means the power factor is above 0.5, one zero means exactly 0.5, and one negative means below 0.5. Readings can be in kW or W, just keep both the same.
Phase Sequence Identifier
Enter the three phase angles in degrees to see whether the rotation is positive A-B-C or negative A-C-B, and how to flip it.
Positive sequence. A motor on this rotation turns in the normal direction.
Phases follow A then B then C, the standard positive sequence. A motor wired to this rotation turns in the normal direction. To reverse it, swap any two of the three line leads.
Enter the angles your meter or one-line shows. The default 0, 240, 120 is a balanced positive sequence. Swapping any two angles flips the rotation, the same way swapping two leads reverses a motor.