Parallel conductors — two or more conductors per phase run in separate raceways — are required by NEC 310.10(H) for conductors 1/0 AWG and larger, and commonly used on high-ampacity feeders. When conductors are run in parallel, the effective circular mil area is multiplied by the number of sets. For example, three parallel sets of 500 kcmil copper have an effective CM of 1,500,000 for voltage drop purposes. The voltage drop formula adjusts accordingly: VD = K × I × D / (CM × number of sets). This calculator handles the parallel-set math automatically so you get an accurate voltage drop without manual multiplication of circular mil areas.
For a 480V 3-phase 400A feeder at 200 ft using 2 parallel sets of 500 kcmil copper: effective CM = 1,000,000. VD = 1.732 × 12.9 × 400 × 200 / 1,000,000 ≈ 1.79V (0.37%). Well within NEC limits.
This is a variant of the full Voltage Drop Calculator — which supports all phases, wire materials, and distances in a single tool.
Try all options in the full Voltage Drop Calculator →