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Wire size for 20 amps at 125 feet

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20 A at 125 ft one-way

VoltageConductorMinimum sizeVoltage drop
120 VCopper6 AWG2.46 V (2.05%)
120 VAluminum4 AWG2.54 V (2.12%)
240 VCopper10 AWG6.05 V (2.52%)
240 VAluminum8 AWG6.30 V (2.62%)

Smallest size meeting NEC 75 °C ampacity (with 240.4(D) limits) and ≤3% drop at the full 20 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 20 amps at 125 feet?

At 240 V: 10 AWG copper keeps voltage drop under 3%. See the table for 120 V and aluminum.

Same current, other distances

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