wiring device termination temperature

[kwired]

But conductor ampacity has most everything to do with rating of the insulation not the conductor itself. The terminal temp rating wont care what insulation is on the conductor, it cares how many circular mils of copper make up the conductor.

If you use 60C ampacity chart to select the conductor you get more circular mils of conductor then you will using the 75C chart for same ampacity level.

I really don't see the point of dual temp termination rating, or at least have not heard a good explanation of why such dual rating exists. 60/75C terminal can accept the heat produced by a conductor applied at 75 C rating, but if you apply a 60C conductor - it will be larger conductor for purpose of producing less heat because of the lower temp insulation rating. The general rules of 110.14 already are sufficient to not need to dual rate it IMO. If not marked the rules in 110.14 dictate temp rating, if marked the higher rating is acceptable if using higher rated conductor, no point in marking with lower rating.

All you quoted was essentially device instructions, nothing that tells us why the 60/75C terminal rating exists.

I don't know how easy I made it to understand what I wanted to say here. Let me give an example.

Say you have a 50 amp receptacle/50 amp branch circuit device.

1. If either device is designated 60C then you are running conductor sized from 60C table which will give you minimum of 6AWG copper.

2. If both devices are rated 75C then you can run 8AWG copper - if the insulation on the conductor is also 75C, if insulation is only 60C you are still going to use 60C table and will need 6AWG minimum.

3. If both devices are dual rated 60/75C your minimum conductor size is determined by conductor insulation rating.

Situation 1 gives you the 60C result no matter what.

Situations 2 and 3 give you either 60 or 75C depending on thee items:

A. terminal temp rating at beginning of run

B. terminal temp rating at end of run

C. conductor insulation temp rating

I think the marking of 60/75C on a device is just a reminder that it can be used with either conductor rating but doesn't really need to be there as code already says it can be either as long as it isn't marked 60 only.