60C or 75C?

[evalencia01]

Assuming no termination rating, Amps>100A is 75C and Amps<100A is 60C, but what if the load is 115A, which means we use 75C, and the neutral load is 90A, would we use the 60C column in this scenario even though it'd be the same wire size? I'm assuming that on an exam yes, but any other insight is appreciated.

 

[SSDriver]

In real world almost everything is 75c(90c for conductor adjustments only) above or below 100A unless its just wire connectors or power distribution blocks in an enclosure without other equipment then you can possibly use 90c based off of termination ratings.

As far as exams go this is tough as exam questions aren't always black and white and the answer they want may not be correct. I would calculate the way you said with 115A at 75C and neutral at 60c (assuming this is a panel your calculating as any single load current should be the same for ungrounded and neutral).

 

[Carultch]

Read NEC 110.14(C)(1)(b), where the conditions give you 75C as the default rating. It indicates "equipment rated for circuits over 100A", rather than circuits rated for over 100A. It also states "or marked for conductors larger than #1".

If you have a 125A panelboard, and you are only connecting a 90A circuit to supply its main lugs, it is still equipment that is rated for over 100A, and therefore has a 75C default rating. You don't have to fully utilize its 125A rating, in order to take credit for 75C being the default. Once equipment is rated for over 100A, and has a 75C rating, it has that 75C rating even when its ampacity is only partially used.

Most equipment 100A and larger will also have terminal provisions for up to #1/0 or possibly larger, which is another reason why it would have a 75C default rating. Given the same terminal that can take both aught sizes and gauge sizes, that particular termination has the same terminal temperature rating regardless of what size you connect. If it is rated for 75C with 1/0 connected, then it is also rated for 75C when #3 is connected. That is, unless the product instructions specifically tell you otherwise.

 

[Carultch]

There is an ambiguous case created by the OR statements. It is unlikely that it would exist in practice, because 110A is a rare rating, and anything over 100A will likely have terminals for at least #1/0 anyway.

Consider 110A equipment that has a #1 max terminal size, and no documented terminal temperature rating. The underlined part indicates which half of the OR statement applies to this example. Both parts (a) and (b) have a part of their OR statement that applies to this example.

110.14(C)(1)(a):
Equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, [...] 60°C ampacity.

110.14(C)(1)(b):
Equipment is rated for circuits over 100 amperes or marked for conductors larger than 1 AWG, [...] 75°C ampacity.

 

[Hv&Lv]

This thread answered my question about the premade #3 generator cables..