Good morning code enthusiasts, Where cable tray is covered with solid unventilated covers, Section 392.80(A)(1)(b) say that the Ampacity of Multi-Conductor Cables in Cable Trays shall be derated to 95%. The contractor wants to use this type of unventilated cover but make it larger than the tray to allow airflow over the cables, and not use the 95% derating factor.
Would this be acceptable? I don't see anything in the code allowing the cover to be oversized to avoid the derating factor. If anything, I think this could possibly be a UL listing issue, but the code doesn't seem to permit this. Best. Clive T.