NM has to use the 60 degree column, why doesn't SER?

[Luke Neilson]

Title just about says it all. I know I have to use the 60 degree column when looking at non-metallic sheathed cable, but I've never heard that I have to when looking into SER feeder cable. It

 

[electrofelon]

Title just about says it all. I know I have to use the 60 degree column when looking at non-metallic sheathed cable, but I've never heard that I have to when looking into SER feeder cable. It

Well actually the NEC went thru a decades long period of hand-wringing over this issue where they reduced the ampacity of SE to the 60 degree, then changed it to 60 if embedded in insulation, then put it back to the way it was at 75 degree (I think that was what happened over three code cycles, but I may have lost track).

 

[Carultch]

Well actually the NEC went thru a decades long period of hand-wringing over this issue where they reduced the ampacity of SE to the 60 degree, then changed it to 60 if embedded in insulation, then put it back to the way it was at 75 degree (I think that was what happened over three code cycles, but I may have lost track).

I can understand limiting the rating of the cable because it is routed in thermal insulation, because it by definition impedes the ability to disperse its heat. But it seems like thermal insulation is "out of the picture" for anything that would affect its terminations.

I would think, from the physical basis for such a rule, that it would be a derate factor that applies to its (usually) 90C conductor rating, rather than the termination. Like an ambient temperature adder for being inside thermal insulation.