What Size Wire for 30 Amps at 100 Feet?

Answer
8 AWG copper

At 100 ft one way on a 240 V circuit, 8 AWG copper keeps voltage drop at 1.91%, under the recommended 3%. Ampacity alone would allow 10 AWG, but voltage drop decides the size at this distance. In aluminum, use 6 AWG.

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A
%
3% branch, 5% total (NEC note)
Phase
Conductor
Recommended wire
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How we calculated this

    For estimating and educational purposes only. Results are approximate and are not a substitute for a licensed professional, the manufacturer's instructions or your local code. Disclaimer

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    Voltage drop by wire size (30 A, 100 ft, 240 V)

    Copper wireDrop (V)Drop (%)Within 3%
    10 AWG7.26 V3.02%✗
    8 AWG4.58 V1.91%✓
    6 AWG2.95 V1.23%✓
    4 AWG1.85 V0.77%✓
    3 AWG1.47 V0.61%✓

    Voltage drop = 2 × 100 ft × 30 A × resistance ÷ 1000. Keeping it under 3% on branch circuits (5% total) is the NEC recommendation in the informational notes to 210.19 and 215.2.

    Frequently asked questions

    Is 10 AWG enough for 30 amps at 100 feet?

    It carries 30 A, but at 100 ft the voltage drop is 3.0%. That is over 3%, so the next size up is recommended.

    Does the distance include the return wire?

    No. Enter the one-way distance; the formula already counts both conductors.

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