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Wire size for 20 amps at 300 feet

20 A at 300 ft one-way

Voltage	Conductor	Minimum size	Voltage drop
120 V	Copper	3 AWG	2.94 V (2.45%)
120 V	Aluminum	1 AWG	3.04 V (2.53%)
240 V	Copper	6 AWG	5.89 V (2.46%)
240 V	Aluminum	4 AWG	6.10 V (2.54%)

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.

Adjust the numbers

Load current (amps)

One-way length (feet)

Voltage

Conductor

Max voltage drop (%)

Continuous load?

FAQ

What size wire for 20 amps at 300 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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