NM cable thru studs

Status
Not open for further replies.
Re: NM cable thru studs

First I have run into this problem too. And when I tell the AHJ that we are allowed to use table 310.16 to derate from he acts surprised. and with 310.16 a #14 is allowed 25 amps to start with and would take a 60% derating to get to the 15 amps that we are required to protect the circuit with anyway so this alone will allow 9 current carrying conductors "bundled" But I don't believe, that if you can keep the runs loose enough to separate them after each stud or joist it is bundled. Otherwise the floor joist or wall studs would look like swiss cheese.
 
Re: NM cable thru studs

The thing that bothers me about this is that NM cable is usually the cable that is bundled the most and it is used mostly in dwelling units. Dwelling units generally have severely under loaded circuits. If you bundled all of the conductors leaving a panelboard as tightly as you wanted, you would still not have a heating problem in 99 44/100% of the cases. :D
 
Re: NM cable thru studs

This is a very interesting topic. This sounds like an area that should be specifically spelled out in the NEC.
 
Re: NM cable thru studs

Royta,

I agree. There are many safety issues that the NEC hasn't defined. The 310.15 bundling is an example of a blanket rule as Charlie mentioned earlier. A lot of the workmanship problems with cabling installation that occur end up in sections such as 310.15. that the local AHJ redefine. I have seen a lot of these bandaids because of actual life safety issues that occur time and again.

Just one example of bundling that I have experienced in new construction occured in 1974. The NEC at that time did not cover bundling as we know it today and still doesn't. Home run installations were bundled into one single trunk in the attic subsequently pulled down into the main panel below.

The incident I remember clearly was a custom home wired with a 10 cable bundle through a length of the roof soffit. A 20' run went up in smoke due to a shorted load and a hung up panel breaker. The circuit had literally fried in the middle of the trunk and took out the surrounding branch circuits next to it.

Lucky there were no injuries but the AHJ in that locale made sure main trunk bundling was no longer allowed. I can relate to many more incidents that only older experienced electrical wiremen appreciate. I guess my fervor of NEC interpretation leans toward the safe side.

rbj, Seattle
 
Re: NM cable thru studs

Originally posted by charlie:
... If you bundled all of the conductors leaving a panelboard as tightly as you wanted, you would still not have a heating problem in 99 44/100% of the cases. :D
Click to expand...
I disagree. I think it would be more like 99 11/25% :D
 
Re: NM cable thru studs

Might that 44/100th come from a DMM fuse as used by Fluke?

Roger
 
Re: NM cable thru studs

Originally posted by gndrod:
Bundling is not prohibition, just realize that derating must be proven to comply to the adjustment factors of 310.15(B)(2)(a)

rbj, Seattle
Click to expand...
Keep in mind the ampacity of NM cable for derating starts at 90 Deg C.
 
Re: NM cable thru studs

Ohhhhh! Now that you mention it, yes I do remember that. How old do you have to be for this? ;)

Roger
 
Re: NM cable thru studs

Ooops, your busted Charlie :D

Roger
 
Re: NM cable thru studs

Does anyone else remember back when we used a 2 inch MA and a 2 inch piece of pvc about 2 or 3 feet long out of a panel into ceilings ? Did it ever cause a problem ?We crammed them all in
 
Re: NM cable thru studs

Wayne, the term "Chimney" is a new one on me, but would be appropriate.

Roger
 
Status
Not open for further replies.
Top