Steve, I understand the distinction for <24" nipples but 334.80 doesn't seem to.
The way the code is written and enforced it applies to a 2x4 header over a hollow bay that has a foamed draft stop in the bored hole.
The NEMA report on foam and NM-B seems to dispute this assertion that there is a problem but the rule still lingers on in 2008. In fact they point out the 310(A)(2) exception does not apply.
I will go look at the ROP when I get a minute and see what they were thinking.
