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When every thing connected to it is also rated 90 deg or higher, there are not many times that this would ever be the case.

Roger
 
There was an excellent article published by Fred Hartwell in EC&M magazine in the March 1998 edition titled "The Middle Of The Wire Isn't It's End" which provides the best explanation that I have found regarding wire derating and connection requirements. Some of the NEC references have changed due to the new code, however the basic information is still relevant. You can probably find this in the archive section on their website: www.ecmweb.com

I have never had an occasion where the 90 deg column could be used due to the limitation of the connection.
 
The Middle Of The Wire Isn't Its End

The Middle Of The Wire Isn't Its End

LarryFine said:
Any idea how to find the archives? :-?
Click to expand...

It's a trade secret..but here's the story:
[The Middle Of The Wire Isn't Its End]
Mar 1, 1998 12:00 PM, Frederic P. Hartwell
​

The temperature restrictions in the Code for terminations have nothing to do with how you figure ampacities over the length of the circuit. Here's a contractor-focused review of both.

If we don't do anything else in this trade, we all select, install, and terminate conductors. We've seen many misconceptions over the years, and they usually involve confusing the middle of a wire and the end of the same wire. Now, you probably think you know the difference, and you do. Just be sure you keep that difference in mind when you select your conductors.
Click to expand...

Happy reading :)
 
roger said:
When every thing connected to it is also rated 90 deg or higher, there are not many times that this would ever be the case.
Click to expand...

There are no UL listed overcurrent protective devices rated for use with ampacity from the 90C column. Many items require 90C wire and lugs but all of them them are limited to the amps in the 75C column.

I believe the only items rated for the 90C column ampacity are "splicing and joining" items like wire nuts and distribution blocks.
 
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