ECN Forum Forums Code Related Discussion NEC & other Code issues Ampacity issue for Romex?

Hmmm ... maybe that's the cause of the confusion .. the real cause of the 'scorched wires.'

Foams, whan they cure, give off heat. In a foam-in install, temps inside the foam can exceed 200F easily ... which is about where PVC (what makes the outer jacket) starts to break down.

Maybe, just maybe .... they're fixing the wrong problem???

I am not even sure we should be using that foam in the first place. Some of it is pretty nasty when it burns. In my wife's typical 2500-3000 sq/ft house they would shoot 6 or 7 cans of that foam, based on the dead soldiers I saw laying around.
The MSDS for "Great Stuff" says combustion products include but are not limited to oxides of nitrogen,isocyanates, hydrogen cyanide, CO and CO2.

Now that I have the actual 2008 code book and can read the full text of article, it’s clear that 334.80 refers directly to Table 310.15[B][2][a] and not to article 310.15 itself, so the 24-inch rule doesn’t apply to in the case of running multiple cables through the same hole.
I guess we will need to drill more holes to keep the number of current carrying conductors in each hole to 9 or less, for the 70% ampacity adjustment, to avoid having to upsize the conductors. Seems like it shouldn’t be too difficult to comply with this.

K, I won't say you're wrong ... or that I disagree with you ... or, for that matter, anyone else in this thread. The NEC is so poorly written, with such bad grammar, that I'm not sure what it's trying to say.

As I read the references, it's saying "if you drill a hole more than 2 ft long through wood, pull a cable through the hole, and cap it with foam, you have to treat those wires as if they were in pipe."
That's a very long drill bit!

What I think they were trying to say was "If a wall cavity is more than 2 ft long, is packed with insulation, as well as sealed with foam, we want you to consider the cavity as if it were pipe." That sort of makes sense ... but that's not what the code says.

As I see it, this issue only arises immediately above, and below, a panel - and then, only if the panel is on an outside wall.

I once worked for a company that is very heavily involved in the code process. Their Personnel Director made it clear that they only were interesting in hiring engineers and accountants. "What good is an English degree?" was the comment made. (No comment on that example of poor grammar! ) Well, looking at our codes, I think there is a greater need than ever for code panels to include someone with a degree in English!

You probably get more guidance from the ROP and ROC. They make it clear they are taking about any penetration through any framing member if it is sealed with insulation or "caulk".

There's some discussion of this on page 49 of this months (Jan. 8) issue of Electrical Contractor magazine. That article supports what KJay is saying.

Just to clarify I meant what KJay is saying in his 1/3 & 1/14 posts.

Did y'all see this?
http://esteroriverheights.com/electrical/nema_romex_in_foam_study.pdf