I don't believe so. But if the circuit has no change in conductor size, and the OCPD termination is only rated 75C, then you are limited to the 75C table values. I'm not familiar with MV OCPDs and whether they allow 90C terminations using the 90C ampacity, although I guess they must since the tables in 315.60(C) only have 90C and 105C columns.Hello, in the Canadian Electrical Code there is rule 28-104(1)(c) which requires motor feeder cables to be sized based on 75C ampacity values. Is there an equivalent rule in the NEC?
Did you mean 0.866? That's sqrt(3)/2, which is the correct adjustment factor to go from a 90C ampacity based on 30C ambient to a 75C ampacity based on 30C ambient. Because the allowable temperature rise goes from 60C to 45C, which means the allowable current goes down by a factor of sqrt(45/60) = sqrt(3/4) = sqrt(3)/2. [The sqrt is because heat generation varies as current squared, while heat dissipation varies linearly with the temperature difference.]Is there a derating factor to apply to the values in the 315.60(C) tables to get a 75 C ampacity value? For example, the corresponding table for shielded 5 kV cables in the Canadian code uses a 0.886 factor to convert from 90 C to 75 C values.
