Motor Derating for Voltage Unbalance (NEMA MG-1)

Turns a measured three-phase voltage unbalance into a NEMA MG-1 motor derating factor and the do-not-operate flag above 5%: unbalance = max deviation from the average / the average (460/455/450 V -> 1.1% -> derate ~0.98). The MG-1 curve is interpolated; above 5% the motor should not be operated. Correct the unbalance source first; the manufacturer and MG-1 govern the final figure.

v_avg = (Vab + Vbc + Vca)/3; unbalance% = max deviation from v_avg / v_avg x 100; derate_factor read off the NEMA MG-1 curve (1% -> ~0.98, 5% -> ~0.75), interpolated; over 5% -> do not operate.

Motor derating for voltage unbalance, NEMA MG-1; the unbalance per the NEMA definition (max deviation from the average over the average), by name.

The NEMA MG-1 derate curve is read off the standard; above 5% unbalance the motor should not be operated. The manufacturer and MG-1 govern the final figure; correct the unbalance source first.

Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.

Field names used by the API: v_ab, v_bc, v_ca, unbalance_pct, derate_factor

• Unbalance definition maximum deviation of any line-to-line voltage from the three-phase average, divided by the averageNEMA MG-1 voltage-unbalance definition
• Derate curve the bundled MG-1 derating points (1/2/3/4/5% -> ~0.98/0.95/0.88/0.82/0.75), linearly interpolatedNEMA MG-1