Sorry to everyone for "beating a dead horse" but our a senior electrical engineer who I work with sent this email out to all the electrical engineers in our group and I just wanted to get your take on it...
"Here?s the NFPA response to the subject issue. As discussed below termination ambient temperature ratings need to be derated.
The latest NFPA ? 70 handbook 2014 edition relating to Article 110.14C on page 34 states ?Conductor terminations, as well as conductors, must be rated for the operating temperature of the circuit.? For example, the load on a 8 AWG THHN, 90Deg. C copper conductor is limited to 40 amperes where connected to a disconnect switch with terminals rated at 60 deg. C. The same conductor is limited to 50 amperes where connected to a fusible switch with terminals rated at 75 Deg. C. Not only do termination temperature ratings apply to conductor terminations, but the equipment enclosure marking must also permit terminations above 60 Deg. C. This is a change from the 2011 Code.
The question posed to NFPA. Is it required to adjust conductor terminations for ambient temperatures?
I contacted {name removed} of NFPA on 8/18/14, 1-800-344-3555 pertaining to obtaining an interpretation of the aforementioned code requirement. His interpretation was YES, that adjustments for conductor terminations for ambient temperatures has to be accounted for.
The temperature correction and adjustment factors apply to the ampacity for the temperature rating of the conductor, provided the corrected and adjusted ampacity doesn?t exceed the ampacity for the temperature rating of the termination per the provisions of 110.14(C). Put another way, this change clarifies that, after applying these adjustments and corrections, the resulting ampacity still can?t exceed the temperature limitations of the equipment termination.
The ambient temperature ratings of all devices need to be verified with the manufacturers to ensure that ambient temperatures are accounted for. Most electrical devices such as breakers have been rated for 40 deg. C ambient however other ambient temperatures may be used and as a result the most conservative approach for the limiting device for the circuit is to be used. So if you have a device with terminations rated for 30 Deg. C ambient and the circuit will be in a 40 deg. C ambient the termination must also be derated as well.
As an example, if you had a 40 deg. C ambient condition and a circuit breaker back feeding another circuit breaker say in an MCC and the circuit was greater than 100 amps you would use the 75deg. C rating of the termination. The ambient temp. rating of the circuit breaker would typically be rated for 40 deg. C. Per Article 110.14C you would use table 310.15(B). According to John for conservatism, this temperature rating table are for cable ampacities in a 30deg. C ambient even though the ambient temperature of the circuit breaker is at 40 deg. C you need not adjust for the increased ampacity. So you could select a #2 Awg. 90 deg. C cable and if it were in a 40 deg. C ambient would have to be derated by .91 or the cable ampacity would be 130 amps X 0.91 = 118.3 amps. The termination would be rated for 75 Deg. C so For a #2 cable the 75 deg. C ampacity is 115 amps. Since the termination at the circuit breaker is rated for 40Deg. C no other adjustment is required as noted by John, the 115 amp would be the maximum rating of this circuit to be considered.
If the circuit breaker termination was rated for another ambient i.e. 30 deg. C, ampacity adjustments for the termination must be used to account for a different ambient temperatures.
Hope this clears this issue."
