Voltage Drop Calculator
Size a run against the NEC's 3% recommendation. Updates as you type.
How it's figured
Single-phase: VD = (2 × K × I × L) ÷ circular mils. Three-phase uses √3 instead of 2. K ≈ 12.9 (copper) / 21.2 (aluminum) ohms·cmil/ft. The NEC recommends ≤3% on a branch circuit (≤5% total feeder + branch) in informational notes. It's guidance, not a hard rule.
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