Three-phase voltage drop calculations differ from single-phase because the effective length multiplier changes: you use a factor of 1.732 (the square root of 3) rather than 2. For a balanced three-phase feeder, voltage drop equals 1.732 × K × I × D / CM, where K is the resistivity constant (12.9 for copper, 21.2 for aluminum at 75°C), I is the load current in amps, D is the one-way circuit length in feet, and CM is the conductor cross-section in circular mils. The NEC recommends keeping total voltage drop under 3% for branch circuits and 5% total for feeders plus branch circuits combined. SparkShift's voltage drop calculator handles both single- and three-phase modes automatically.
For a 480V three-phase feeder at 80A, 250 ft, 4 AWG copper: VD ≈ 1.732 × 12.9 × 80 × 250 / 41,740 ≈ 10.7V (2.23%). This stays within the NEC 2% feeder recommendation.
This is a variant of the full Voltage Drop Calculator — which supports all phases, wire materials, and distances in a single tool.
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