Quote Originally Posted by kwired View Post
Also applies to conductors and cables that are bundled together for more than 24 inches.


Correct, nipple length can be up to 24 inches without derating. Same with NM or any other cable. The change is with NM cable and bundles that pass through a hole that is sealed by some manner for firestopping, air infiltration, etc. There is no mention of length, so it applies to any hole that gets sealed up. Pass same cables through a hole that does not get sealed up and you are back to the 24 inch nipple rule that has been around for a long time.
Exactly and if your under the 2005 code cycle where this requirement first appeared then you do not have to derate for the cables in the filled hole since they didn't not eliminate the application of 310.15(A)(2)Ex. until the 2008 NEC. Under the 2005 NEC this requirement was not enforceable.