How do I size a three-phase or motor circuit?
Three industrial checks: 3-phase voltage drop, line current from kVA, and a motor's full-load amps with breaker and wire.
Result
1.1% drop
5.4 V lost on 8 AWG (3-phase) · target ≤ 3%
Within 3%
Smallest wire under 3% here: 8 AWG
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How is this calculated?
Using the tool
Industrial power, three checks: voltage drop on a 3-phase run, line current from a kVA load, and a motor's full-load amps with its breaker and wire. Switch modes above. Copper assumed.
The formulas
Three-phase voltage drop = √3 × K × I × L ÷ CM: K = 12.9 for copper, I the line current, L the one-way length, CM the conductor's circular mils. The √3 (≈1.732) replaces the 2 used for single-phase. Target is 3% or less for a branch circuit.