Construction Electrician First Class (SCW), Retired

Tool 02 / Wire gauge

Size for ampacity and the run.

Find the first conductor that meets the 75°C ampacity value and a voltage-drop target. The larger of the two requirements wins.

A
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Base ampacity uses the 75°C column of NEC 2023 Table 310.16, no more than three current-carrying conductors, and 30°C ambient. Small-conductor overcurrent limits are applied. Temperature, bundling, terminals, motor rules, and other project conditions can require a larger conductor.

Reference overview: NEC 2023 Table 310.16 ampacity matrix. Verify the adopted code edition and local requirements.