Re: Which enclosure???
It is of my opinion that the main enclosure must be listed with the internal enclosure inside of it. If added after then would the main enclosure still comply with its listing would be the question. Technically most likely no.
Should one consider the internal enclosure one might consider its own listing as being tested in an open air environment at a specific ambient temperature to assure that the internal components are kept within their temperature ratings. When placed inside another enclosure then heat within that enclosure would then affect the temperature of the components within the second enclosure.
However, all the technicalities aside it probably would come down to what the AHJ interprets it to be. He may conclude that the main enclosure is UL listed and as long as the second enclosure is UL listed it's OK. However, even it one were to add a simple UL listed component such as a relay to the main enclosed control if that component isn't included within the enclosed control manufacturers UL listing for that assembly that added component probably would violate the UL listing.
