How do I read the 310.16 ampacity table?
Pick the row by conductor size, then the column by the insulation temperature rating, copper on the left half and aluminum on the right. Read the ampacity at that intersection, then apply any correction for ambient temperature or for more than three current-carrying conductors. The raw table value is the starting point, not the final answer.
Last reviewed June 2026 · Answered by JourneymanIQ staff
Row by size, column by temperature
Find your conductor size down the left, then move to the column for the insulation rating, like 75 degrees C for THWN-2. Copper is the left set of columns, aluminum and copper-clad aluminum the right.
Read the base ampacity
The number at that intersection is the base ampacity before any adjustment. A 10 AWG copper conductor at 75 degrees C reads 35 amps, for example.
Apply corrections last
Adjust for ambient temperature from the correction factors and for more than three current-carrying conductors from the adjustment factors. The termination rating can also limit you, so the final ampacity is the lowest of the limits.
Size for the row, temperature for the column, then correct for ambient and conductor count.
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