I don't recall ever seeing heat damaged insulation under these conditions, either in a wireway or panel enclosure. Of course, one man's experiance is a very limited database.

I could see where this might be a problem with conductors that are loaded on a continuous basis. I feel there are two factors that prevent damage most of the time, the first being are loads that are not continuous in nature. the second is that many conductors are already oversized based the actual load and requirements of limiting small conductors per 240.4(D) to a value lower than their actual ampacity.

Tom

Few things are harder to put up with than the annoyance of a good example.