Originally Posted by
donf
Depending on the type (insulation) and connection listed temperatures the max at a 60(C) would be 40 amps. If you are using a cabled listed for 75(C) in a circuit with components also listed at 75(C) then the max is 50 amps.
I agree that this cannot be answers accurately without more detail.
The above quote is basically correct.
NM or SER cable must use the 60 deg C column in figuring amperage, so #8CU would be rated for a 40A circuit.
#8CU conductors in conduit would use the 75 deg C column since regardless of the fact that wire is rated for 90 deg C there are very few if any 90 deg C terminations and circuit breakers rated for 90 deg. MC cable also fits this description.
This would allow #8CU on a 50A circuit.