338.10(B)(4)(a)(3)

[Jimmy7]

Massachusetts amended the 338.10(B)(4)(a)(3) in the NEC to state “Where installed in thermal insulation, the ampacity shall be in accordance with the 60 degree C (140 degree F) conductor temperature rating. The maximum conductor temperature rating shall be permitted to be used for ampacity adjustment and correction purposes, if the final derated ampacity does not exceed that for 60 degree (140 degree F) rated conductor“.

With this being said, I need to run some SE cable behind a wall with thermal insulation. I was thinking if I sleeve it in PVC where there is thermal insulation (About 15’) I could still use the SE cable at 75 degrees. Will that work in your opinion? Do I need to be concerned about heat dissipation sleeving it in PVC?

 

[Electromatic]

I would think this similar to the rule of: The inside of conduit in a wet location is considered a wet location, and the 75° could not be used.
That said, the code for SE ampacity has changed so many times, I'm sure some would let it fly.

 

[Rick 0920]

I don't know for sure, but I'm thinking that this amendment is for heat dissipation. Whether you sleeve it in conduit or not, the heat created by current flow plus ambient will still be there whether it's in conduit or not. This seems similar to the bundling requirement. We don't have to derate if we have air space between cables, but if we bundle them, the heat can't escape. The fact that the insulation will trap the heat in is probably the reason for the 60 C requirement.