Can a conductor have a different temperature rating at each end?

[JoeStillman]

What's wrong with this picture? What if I go right to cable tray with no conduit? How long do the 2-per-Ø conductors have to be before I can splice them?View attachment Ampacity Test.jpg

 

[petersonra]

What's wrong with this picture? What if I go right to cable tray with no conduit? How long do the 2-per-Ø conductors have to be before I can splice them?View attachment 2557579

The conductor does not have a different rating. The termination does.

 

[JoeStillman]

The conductor does not have a different rating. The termination does.

Fair enough. But how far apart do the terminations have to be? If one termination is operating at 45°C rise over 30°C ambient, and the other end of the wire is operating at 60°C rise, there will be heat transfer from higher to lower temperature. What's to keep the 75° lug from being a heat sink for the 90° H-tap? It seems like cable length ought to matter. Is there anything in the code about this?

 

[GoldDigger]

Fair enough. But how far apart do the terminations have to be? If one termination is operating at 45°C rise over 30°C ambient, and the other end of the wire is operating at 60°C rise, there will be heat transfer from higher to lower temperature. What's to keep the 75° lug from being a heat sink for the 90° H-tap? It seems like cable length ought to matter. Is there anything in the code about this?

First of all, the Code itself makes no allowances at all for heat sinking of a termination through the attached wire(s).
Second, the temperature rating of a termination indicates the maximum temperature to which that termination is allowed to be heated under normal use. There are several different criterea which factor into this calculation, including the mechanical characteristics of the termination itself and the termperature sensitivity of attached components.
Third, the UL test procedure for determining the wire ampacity and temperature rating required for termination in a piece of equipment uses a specific open ended length of conductor attached to the termination. I think something like 3 feet.

So, I would expect that as long as the wire is longer than roughly 6 feet, use of the 90 degree ampacity at one end will not have any practical effect on the 75C ampacity calculation at the other end of the circuit.

 

[bwat]

There's that section that that allows you to use 90°C terminations if it's outside of the enclosure. That may provide some insight here. Upon quick search, I couldn't find which section that was. Here's the picture that I remember from it: