Joe posted this proposed change a while back:
Proposal 6-31
Revise Section 310.15(B)(2)(a)
The proposed revision to this section adds a more restrictive requirement to apply ampacity adjustment factors where more than two NM cables containing two or more current-carrying conductors each are bundled together and pass through wood framing members where fire-stopping or draft-stopping material is installed at the penetration. The ampacity adjustment factors specified in Table 310.15(B)(2)(a) would be required to be applied to the current-carrying conductors installed in this manner.
Does this mean that the ampacity of NM conductors need to be adjusted anytime more than 2 cables penetrate the top plate even though its only 3"?
I have never been very concerned about derating multiple NM cables passing through single holes since they are usually not bundled tightly between the holes. The product Dave Nix was showing us was able to get a UL listing for quite a few cables without having to adjust the ampacity. I think there would be more heat in that enclosed raceway than in a stud or joist bay.
Curt
