Temp derate for conductors with lower temp rated lugs.

[Jeff S]

NEC 110.14(C) seems to me to indicate that you use the temperature derate factor from the column of the conducter you're using (such as 90C) and then compare the resultant ampacity to the ampacity in the 75C column (if that's what your connections are rated). This is how I've been doing the calculation. I've come across another source though that says you should use the temp derate from the terminal temp column even though the conductor has a higher temp rating. Can anyone settle this for me?
Thanks,
J.S.

 

[charlie b]

You start with the value in the column (i.e., 60, 75, or 90) that corresponds to the rating of the insulation of the conductor. If your conductor has THHN insulation, you start with the value in the 90C column. If you conductor has THW insulation, you start with the value in the 75C column. Then you apply the derating factors (i.e., for temperature, or for more than three CCCs in the raceway, or for both conditions). Finally, you compare the resulting value with the value in the column that corresponds with the rating of the terminations. If the terminations are rated for 75 (the most common rating), then the final ampacity can't exceed the value in the 75C column. If the terminations are rated for 60, then the final ampacity can't exceed the value in the 60C column.

 

[Jeff S]

Thanks, that's exactly how I've been doing it but ran across the different version in a training class document. As I expected they were just teaching it wrong. I appreciate you clarifying that for me.

 

[thetacon]

on service gear if the main has a 75 degree rating it limits the C.C.C. wire rating. But Is that true of the neutral which lands on a lug? It is my understanding that it can be sized off the 90 degree as long as the lug is rated 90 degree which most of them are is that correct?

 

[stevebea]

on service gear if the main has a 75 degree rating it limits the C.C.C. wire rating. But Is that true of the neutral which lands on a lug? It is my understanding that it can be sized off the 90 degree as long as the lug is rated 90 degree which most of them are is that correct?

I could be wrong but I dont think you would find a lug in service equipment rated more than 75 degree C.

 

[acrwc10]

on service gear if the main has a 75 degree rating it limits the C.C.C. wire rating. But Is that true of the neutral which lands on a lug? It is my understanding that it can be sized off the 90 degree as long as the lug is rated 90 degree which most of them are is that correct?

I have yet to see a "lug" that is 90 degree rated. The only connections that I am aware of being 90 degree rated are Split Bolt (kearnys), compression, and wire nuts.

 

[infinity]

Even if a lug were rated for 90? C the equipment it's attached to would also need to be rated for 90? C. So if you had a piece of equipment with 75? C terminals you couldn't simply throw them away and install 90? C terminals and use the conductors at 90? C. Here's a related graphic:

 

[jim dungar]

Lugs are often rated 90?C (i.e. AL90CU), but that is really irrelevant.

NEC 110.14 use the phrase termination not lug. A termination includes the lug plus the device the lug is connected to, as well as the enclosure it is mounted in. The limiting factor is usually the device, so replacing a lug only does not increase the temperature rating of the device.

 

[thetacon]

good to know
thanks

 

[Smart $]

Lugs are often rated 90?C (i.e. AL90CU), but that is really irrelevant.

NEC 110.14 use the phrase termination not lug. A termination includes the lug plus the device the lug is connected to, as well as the enclosure it is mounted in. The limiting factor is usually the device, so replacing a lug only does not increase the temperature rating of the device.

Additionally, don't forget that one wire has two terminations. Even if one end were rated for 90?C, the other end could easily be 60? or 75?C.