NEC 110.14(C)(1)(a)(3)

[RRJ]

Conductors with higher temperatures ratings if the equipment is listed and identified for use with such conductor.

Mike Holt says we could pick wire size based on 75 degree column based on this section. it is confusing to me I wish section 110.14 C1a2 would say use 60 degree column unless the equipment is rated 75 then use 75 column to size wire.


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[Carultch]

You have the onus of proof if you want to use the 75C rating on any equipment 100A and less, otherwise 60C is the default. The onus to prove equipment on both sides meets or exceeds a 75C termination rating. For over 100A, the manufacturer has the onus to specify if 60C ratings are required, otherwise 75C is the default.

The 60C default rule is mostly academic (e.g. when taking an exam). In practice, most equipment is listed and labeled otherwise for 75C, so it is rare that the equipment's lack of a rating requires the 60C column. Some cable types may specifically require 60C termination ratings, such as NM cable (romex).

 

[augie47]

note that 110.14(C)(1)(a)(3) basically states what you want
(C)(1)(a)(2) sim,ply states you can use conductors with a higher temperature rating than termination limitations.

 

[RRJ]

You have the onus of proof if you want to use the 75C rating on any equipment 100A and less, otherwise 60C is the default. The onus to prove equipment on both sides meets or exceeds a 75C termination rating. For over 100A, the manufacturer has the onus to specify if 60C ratings are required, otherwise 75C is the default.

The 60C default rule is mostly academic (e.g. when taking an exam). In practice, most equipment is listed and labeled otherwise for 75C, so it is rare that the equipment's lack of a rating requires the 60C column. Some cable types may specifically require 60C termination ratings, such as NM cable (romex).

What about 240.4 D(3),(5)and (7) the over current protection shall not exceed 14awg-15amps, 12awg-20amps, 10awg-30amps. That’s a 60 degree column rating. I think that’s why I can’t grasp the idea to size 14-1awg 100amps or less with 75 degree column.


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[RRJ]

note that 110.14(C)(1)(a)(3) basically states what you want
(C)(1)(a)(2) sim,ply states you can use conductors with a higher temperature rating than termination limitations.

See to me it just sounds like I could use higher temperature wire if the termination has the same rating. It is not as clear as C1a2

In the other hand 110.14(C)(1)(a)(2) specifies the ampacity of such conductor is determined based on the 60 degree column.


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[Dennis Alwon]

In general the exception is for #14-10 for the overcurrent protective device however there are some cases where we can use 14 for 20 amps loads, #12 can be used for 25 amp loads, 10 for 35 amp loads. We can also use the 90 C col. for de-rating

 

[Carultch]

In the other hand 110.14(C)(1)(a)(2) specifies the ampacity of such conductor is determined based on the 60 degree column, unless terminations on both sides are listed and labeled otherwise.

Added the part in bold, that is the essence of this issue.

This doesn't just mean the lug on the equipment is marked for 75C or 90C, but that the equipment itself is rated for the terminal temperature in question. It is very common that lugs on equipment are clearly marked for 90C, but it doesn't necessarily mean you get to take credit for it. Any time the lug is part of a factory-assembled product, the assembled product's listing and labeling has to tell you what the termination rating is, in order to take credit for it.

In practice, most equipment is listed and labeled otherwise for 75C terminations, so it is rare that equipment lacking this rating governs 60C sizing. The 60C sizing rule is a formality to tell you to first check for a product listing to the contrary, and if you don't find it,go with 60C.

One application where 60C termination sizing is applicable in practice, rather than just applicable in academics, is the use of ROMEX (i.e. NM cable), and other cable types where the NEC specifically requires it. Another example is SEU/SER cable, where routed thru thermal insulation.