Free calculator · AstralLearn
Voltage drop calculator
Long run? Check the drop before you pull wire. Enter the load, distance and wire size — get the drop in volts and percent, plus the smallest size that stays under 3%.
Back to AstralLearnUses the standard K·CM method (K = 12.9 Cu / 21.2 Al). One-way length; the calc doubles it for single-phase and applies √3 for three-phase.
- Voltage drop
- 6.25 V
- Voltage at load
- 233.7 V
Smallest size within 3%: 8 AWG
How it works: the NEC recommends (it doesn't mandate) keeping branch-circuit drop ≤ 3% and total ≤ 5%. We use the K·circular-mil method: drop = (2 or √3) × K × amps × length ÷ CM.
Educational reference — verify against the current NEC and your AHJ. Want it engineered and permitted? Call a licensed C-10 → (650) 562-8594.
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