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WattSimple

Voltage Drop Calculator

Calculate voltage drop over a wire run from gauge, length, current, and voltage — single- or three-phase, copper or aluminum. WattSimple flags the NEC 3% recommendation and tells you the smallest wire that meets it.

Phase

Voltage drop

3.11%

Volts dropped
7.46 V
Voltage at load
232.5 V
Over the recommended 3%. Upsize to 8 AWG copper to drop to 1.95%.

The NEC's 3% (branch) / 5% (total) figures are recommendations (210.19 & 215.2 informational notes), not hard rules. Wire & breaker chart. Confirm with a licensed electrician + AHJ.

Frequently asked questions

This calculator uses the circular-mils method: VD = (factor × K × length × amps) ÷ circular mils, where K ≈ 12.9 for copper (21.2 for aluminum) and the factor is 2 for single-phase or 1.732 for three-phase. Length is the one-way run distance. The result is shown as both volts and a percentage of system voltage.

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