Voltage Imbalance
Three-phase percent imbalance and motor derate factor.
Example
You enter
- Line A voltage (V) 480
- Line B voltage (V) 475
- Line C voltage (V) 470
You get
- Average 475 V
- Max deviation (V) 5
- Percent imbalance 1.053 %
- Motor derate factor 0.97842
- Nema hp derate (%) 2.1579
Checked against published worked examples from: NEMA.
Details, formula, and sources
Formula or table% imbalance = max deviation from average / average × 100; NEMA MG 1 derating table (2/5/12/18/25% HP at 1-5%), linearly interpolated from 0% upward.
Source and editionNEMA MG 1 by name.
Free accessNEMA standards licensed; principles free in IEEE-USA outreach.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesV_a, V_b, V_c, average_V, max_deviation_V, imbalance_percent, derate_factor, nema_hp_derate_pct
- Trip threshold > 5% halts the motor (engineering practice)NEMA MG 1 by name