NM cable thru holes

Status
Not open for further replies.
Strathead said:
Can you elaborate on this? I don't touch Romex if I can help it.:p So I don't see those bags, but I would think those stackers "maintain spacing" and in between studs would be enough to satisfy the bundling requirement. Saying to "observe" 310.15 doesn't necessarily mean the stackers don't maintain spacing. If it does mean that, then at what point are wires or cables no longer "bundled"?
Click to expand...

http://multimedia.3m.com/mws/mediaw..._UoYTSev7qe17zHvTSevTSeSSSSSS--&fn=SIFSDS.PDF

See page two, look for the fine print.

310.15(B)(3)(a)(4) used to be an exception that clarified that cables loosely traveling in the same direction for 24" required derating. Now it's less clear, for clarity, but the principle is still there. Imagine a gaggle of MC cables on bridle hooks - to say they are "touching" much less "bundled" defies common sense, but as far as the Code is concerned, they are. Now remove the MC and replace it with NM - no allowances.
 
Galt said:
Building codes have to have some limit on how big of hole you can make in a joist.I remember seeing a chart of some sort on it. the closer you get to the bearing point the smaller the hole allowed.
Click to expand...

For solid wood:bored holes cannot be larger than 1/3 the actual dimensional height of the lumber, within 2" of any edge. or 2" of another hole. Its IRC 502.8.

TJI: cant remember exactly but iirc the hole cant be bored where the joist sits on a wall or 6" either way from that or the end, and not thru the solid lumber edges or within a 1/2" of it. but a 2x12 joist can have like an 8" hole thru the center of it.

Studs can be drilled a maximum 40% of their actual width, or 60% if not a bearing wall.

Trusses likely cannot be drilled at all, and if so, only in mfg specified areas and sizes.
 
I had several inspectors tell me just that...no more than 3 or derate. I brought up 24 inch raceway rule stating we didn't exceed 24" as a 2x6 is only 1 1/2". They say it doesn't matter..falls under bundling. I say bull but ahj has final say.
On another similar note. During a rough inspection of remodel I mentioned I'd be using the Arlington cable trough/cover stuff. Plastic very similar to panduit. He said be careful and read directions because that's a raceway. I'm not sure if a cable cover is a raceway.
I understand serration and reasons but I think limiting to 3 in bored holes residential is over kill. My reasoning is most of the loads in a home are non continuous so those wires may not even carry current for days.
 
keith gigabyte said:
I had several inspectors tell me just that...no more than 3 or derate. I brought up 24 inch raceway rule stating we didn't exceed 24" as a 2x6 is only 1 1/2". They say it doesn't matter..falls under bundling. I say bull but ahj has final say.
Click to expand...

Unless there's a local rule these guys need to study the NEC. :slaphead:
 
You can have 3 current carrying conductor's before derating so you can have 4- 12/2 or 4-14/2 in a hole and it will not affect the ampacity. In fact you can up to 9 current carrying conductor's in the same hole and you would be fine.

Yes you derate but you derate from the 90C column.
8 current carrying conductor's = 70% so 30 amps X 70%= 21 amps for 12 awg
8 current carrying conductor's = 70% x 25 amps = 17.5 amps for 14 awg
 
In a dwelling in most situations you could use 4-12/3 or 4-14/3 and still only have 8 CCC's. ;)
 
With an I joist floor system for instance the web is only about 5/16"thick. So there you have 4-5 times less than the 1.5" thickness on 2 by's .

My opinion is that there needs to be new verbiage added to the articles that deal with this issue.

The inconsistency in the inspection process is a pita. So many requirements are black and white and you know where you stand.Then you come to this issue and its a mixed bag.

It's ridiculous to have to drill say 8 holes per joist in order to get your runs pack to the panel.
 
keith gigabyte said:
I had several inspectors tell me just that...no more than 3 or derate. I brought up 24 inch raceway rule stating we didn't exceed 24" as a 2x6 is only 1 1/2". They say it doesn't matter..falls under bundling. I say bull but ahj has final say.
On another similar note. During a rough inspection of remodel I mentioned I'd be using the Arlington cable trough/cover stuff. Plastic very similar to panduit. He said be careful and read directions because that's a raceway. I'm not sure if a cable cover is a raceway.
I understand serration and reasons but I think limiting to 3 in bored holes residential is over kill. My reasoning is most of the loads in a home are non continuous so those wires may not even carry current for days.
Click to expand...
I don't like those that say no more then 3. If anything they should say if more then three you better start paying attention. As others have already brought up you won't need to increase conductor size for 90C conductors until you have more then 9CCC's.

I wouldn't call the Arlington trough a raceway, but it still is effective at "bundling" multiple cables IMO. It is not a cable tray either. It is just a chase of sorts - unless there is listing for this stuff that says you can otherwise use different ampacity adjustment then the general NEC rules, then I suppose the listing trumps the NEC, but you must follow instructions.
 
kwired said:
I don't like those that say no more then 3. If anything they should say if more then three you better start paying attention. As others have already brought up you won't need to increase conductor size for 90C conductors until you have more then 9CCC's.
Click to expand...

Paying attention, I like that. Those who say no more than 2 or 3 cables in a hole need to study the actual wording of that section.
 
JFletcher said:
For solid wood: bored holes cannot be larger than 1/3 the actual dimensional height of the lumber, within 2" of any edge...
Click to expand...
They also can't be in the upper or lower 1/3 of the beam, so if the beam is more than 6 inches tall, the edges of the holes need to be considerably more that 2 inches from the edge of the beam.
And where there's a knot, either drill through the knot, or treat the knot as if it were a hole and space your holes accordingly.
(structurally speaking, a knot is every bit as strong as a hole)
 
drcampbell said:
They also can't be in the upper or lower 1/3 of the beam, so if the beam is more than 6 inches tall, the edges of the holes need to be considerably more that 2 inches from the edge of the beam.
Click to expand...
There's no such requirement I'm aware of in the 2015 IBC. Here's the applicable section:

2015 IBC said:
2308.4.2.4 Notches and holes. Notches on the ends of joists shall not exceed one-fourth the joist depth. Notches in the top or bottom of joists shall not exceed one sixth the depth and shall not be located in the middle third of the span. Holes bored in joists shall not be within 2 inches (51 mm) of the top or bottom of the joist and the diameter of any such hole shall not exceed one-third the depth of the joist.
Click to expand...

Cheers, Wayne
 
drcampbell said:
They also can't be in the upper or lower 1/3 of the beam, so if the beam is more than 6 inches tall, the edges of the holes need to be considerably more that 2 inches from the edge of the beam.
And where there's a knot, either drill through the knot, or treat the knot as if it were a hole and space your holes accordingly.
(structurally speaking, a knot is every bit as strong as a hole)
Click to expand...

I think that's for notches, not holes. Notches also cant be cut in the center 1/3rd of the span, iirc (and I probably dont since Ive never notched a joist for electrical work).

eta: didnt see Wayne's post. What he wrote. :p

seta: thank you George for the TJI link. I was pretty close. :cool:
 
Last edited:
Status
Not open for further replies.
Top