derating of conduit and wire run above roofs

[iwire]

Which makes no sense to me. Why change the ampacity of a wire for a difference of 5 degrees of ambient temperature but not for a 30 degree rise because it is laying on the roof in direct sunlight?

Simple, lack of evidence that it was needed.

 

[infinity]

Simple, lack of evidence that it was needed.

If I remember correctly this was one of those sounds like a good idea, theoretical code changes based on the idea that the hot roof would impact the conductors when in fact there was not a lot of real world evidence to support that claim. Sorry to say that the NEC seems to be moving in that direction for several code cycles.