2005 NEC Art. 334.80

[tincan44]

Second paragraph:

"Where more than two NM cables containing two or more current-carrying conductors are bundled together and passing through wood framing that is to be fire- or draft-stopped using thermal insulation or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a)"

The commentary from the Handbook says:
"Section 310.15(B)(2)(a) states in part "or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing and are not installed in raceways, the allowable ampacity shall be reduced as shown in Table 310.15(B)(2)(a)." Failure to comply with the appropriate adjustment ampacity derating called for by this table, where nonmetallic cables may be stacked or bundled, can lead to overheating of conductors. For the 2005 Code a new requirement was added to prevent overheating of Type NM conductors where passing through draft- and fire-stopped material."

Sounds to me like electricians will be drilling more holes and maintaining spacing or be very surprised when they have to apply derating factors to their circuits.

 

[celtic]

Re: 2005 NEC Art. 334.80

Second paragraph:

"Where more than two NM cables containing two or more current-carrying conductors are bundled together and passing through wood framing that is to be fire- or draft-stopped using thermal insulation or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a)"

"Where more than two NM cables containing two or more current-carrying conductors ...."

Sounds to me like electricians will be drilling more holes and maintaining spacing or be very surprised when they have to apply derating factors to their circuits.

How many 12/2's containing 1 CCC could I run through that hole?

 

[infinity]

In general, derating will change the conductor ampacity after you get past 9 CCC's through one firestopped hole. That's quite a few cables. Besides, 310.15(A)(2)exception just about nullifies the 2nd paragraph of 334.80. Drilling more holes than usual to comply with 334.80 isn't really necessary.

 

[tincan44]

Re: 2005 NEC Art. 334.80

How many 12/2's containing 1 CCC could I run through that hole?

I imagine a determined electrician with a 1 1/8" auger bit in, say, a kitchen or over a panel could squeeze in a bunch :shock:

 

[infinity]

Re: 2005 NEC Art. 334.80

How many 12/2's containing 1 CCC could I run through that hole?

I imagine a determined electrician with a 1 1/8" auger bit in, say, a kitchen or over a panel could squeeze in a bunch :shock:

Let's say you had (10) 12-2 NM cables without firestopping in the hole. What would the derated value of the 20 CCC in that hole? Answer is derating is not required since the length of the bundling within the hole is 24" or less.


Now if the hole were firestopped what would the derated value of the 20 CCC's be? Unless any of the cables had a total length of less than 30", the answer is no derating would apply due to 310.15(A)(2)ex. This is because the cables would provide a heat sink effect if the length of the cables within the hole represented only 10% or less of the total cable length. 3" of cable through the wood and firestopped would need a total conductor length of 30" or more to apply the exception to 334.80. Seems highly likely that all the cable conductors would exceed 30" in length.

 

[tonyi]

using thermal insulation or sealing foam

Sounds like if you don't stuff with insulation or foam, and use a firestop caulking instead you can pack'em in with a mallet.

I'm not sure I see any operational difference from the cable's POV.

 

[ryan_618]

Me and a friend of mine named Noel Williams mad completley opposite proposals to this section in the 2008. Mine was to delete it because of the exception to 310.15(A)(2), his was to insist that 310.15(A)(2) exception shall not apply. He won.

Panel 7 doesn't want the exception to be used.

 

[infinity]

Me and a friend of mine named Noel Williams mad completley opposite proposals to this section in the 2008. Mine was to delete it because of the exception to 310.15(A)(2), his was to insist that 310.15(A)(2) exception shall not apply. He won.

Panel 7 doesn't want the exception to be used.

So in 2008, the exception will not apply and in fact derating will be required?

 

[tincan44]

With all due respect to Infinity I have to disagree. I have read 334.80 and where it leads you 310.15(B)(2)(a) numerous times. It does NOT, however, lead you to 310.15(A)(2). I also see 310.15(B)(2)(a) is composed of two different scenarios. One involving a raceway and one involving ??or where single conductor or multiconductor cables are stacked or bundled longer than 600 mm (24 inches) without maintaining spacing?? I would think the ?Point of Transition? is where the cables come together at the entrance to the top plate hole and then are stacked or bundled and stapled (fastened) down the stud frequently for a distance longer than the 24 inches noted in the Code. I believe it would be quite easy to reach the values specified in Table 310.15(B)(2)(a) for derating to apply. They would not necessarily have to be 12-2 single conductor cables, nor would the hole be limited to 1 1/8.

As Ryan stated:
?Me and a friend of mine named Noel Williams made completely opposite proposals to this section in the 2008. Mine was to delete it because of the exception 310.15(A)(2), his was to insist that 310.15(A)(2) exception shall not apply. He won. Panel 7 doesn?t want the exception to be used.?

310.15(A)(2) Exception speaks of "adjacent portions of a circuit." The other articles speak of "single conductor or multiconductor cables." In my thinking that's not exactly the same.

As I read it 334.80 second paragraph DOES apply and in the commentary states ?For the 2005 Code, a NEW derating requirement WAS ADDED to prevent overheating of Type NM conductors where passing through draft- and fire-stopped material. It does, however, seem unclear whether their intent is to apply this only if the hole is 24" or longer or if it will still apply where the cables leave the hole and continue down the wall stacked or bundled more than this distance.