What size wire do I need to carry 100 amps 100 feet?

Carrying 100 amps over 100 feet takes 3 AWG copper or 1 AWG aluminum at the standard 75C rating. At 240 volts that run drops about 2 percent, inside the recommended 3, so ampacity rather than distance still chooses the wire.

For a dwelling service or whole-house feeder, Table 310.12 allows 4 AWG copper or 2 aluminum instead.

The math flips somewhere past 150 feet, where drop crosses 3 percent and the next size up takes over. A 200 foot version of this run wants 2 AWG copper or 2/0 aluminum.

Buried runs at this size are usually aluminum URD for cost; just match the lugs and use antioxidant paste.

The 100 amp run calculator does the ampacity-versus-distance comparison for any length.