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Wire size for 45 amps at 125 feet

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45 A at 125 ft one-way

VoltageConductorMinimum sizeVoltage drop
120 VCopper4 AWG3.46 V (2.89%)
120 VAluminum2 AWG3.59 V (2.99%)
240 VCopper6 AWG5.52 V (2.30%)
240 VAluminum4 AWG5.71 V (2.38%)

Smallest size meeting NEC 75 °C ampacity (with 240.4(D) limits) and ≤3% drop at the full 45 A. Use 125% sizing for continuous loads; apply derating for more than 3 current-carrying conductors or high ambient temperature.

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FAQ

What size wire for 45 amps at 125 feet?

At 240 V: 6 AWG copper keeps voltage drop under 3%. See the table for 120 V and aluminum.

Same current, other distances

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