This is a Code question about Article 338, expect lots of Code cites. Any answer or challenge to answer MUST be well supported with Code cites, committee notes etc.
The allowed temperature of a conductor (60C, 75C, 90C) decides how many amps the conductor can carry. Different insulation types get different temperature ratings. For instance UF cable is rated 60C, but THWN-2 is rated 90C. NM cable is an "asterisk", allowed only 60C in practice, but the 90C figure can be used for certain calculations.
Article 338 is somewhat ambiguous about the thermal rating of SE cable indoors. Here's what it says:
Article 338: Type UF cable
338.10(B)(4) Installation Methods for Branch Circuits and Feeders.
(a) Interior Installations. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 334, excluding 334.80.
Where installed in thermal insulation the ampacity shall be in accordance with the 60°C (140°F) conductor temperature rating. The maximum conductor temperature rating shall be permitted to be used for ampacity adjustment and correction purposes, if the final derated ampacity does not exceed that for a 60°C (140°F) rated conductor.
Article 334: Type NM cable
334.80 Ampacity. The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The allowable ampacity shall not exceed that of a 60°C rated conductor.
Article 334 is for "NM type" cable. 334.80 is the part of Article 334 which alwas limits NM cable to 60C thermal. Excluding that would mean SE is free to run at its normal thermal rating, which means you get to use 75C (if device terminations and any apparatus the cable goes through are good for 75C).
There's no question that SE cable surrounded by insulation is limited to 60C. However…
Notice how the end of the first paragraph (my bold) seems to conflict with the end of the second paragraph (my italic). One waives the 60C requirement and the other imposes it.
- Is the bold phrase entirely redundant?
- Or does the italic phrase only apply to the preceding sentence, and not to interior installations at large?
Note that the italic phrase was deleted in NEC 2008 and was re-added in NEC 2011.
Best Answer
Just about all SE cable you use is not subject to the 60°C limit, unless it's limited by old or cheap terminations
The current (2020 and upcoming 2023) version of NEC 338.10(B)(4) part (a) reads as follows (informational notes omitted, 2023 moves them to the end of the part):
The operative portion here is point 3, which reached its current form in 2017 with the addition of the "10AWG and smaller" restriction. Since SE cable, as a rule, is not even made in those small sizes, that obviates the perceived conflict between the 334.80 exclusion in point 1 and the text in 338.10(B)(4) part (a).
However, this means that we still have to worry about the 110.14(C)(1) termination temperature limit. This isn't an issue for new-build distribution equipment, which is pretty uniformly 60°C/75°C rated, but can be a problem with older panels/breakers (as both the panel and the breaker need to be rated for the higher termination temperature) and some 50A receptacles (generally speaking, cheaper ones -- check the markings on the receptacle to be sure).