Number of wires passing through a wall stud

[Dave Norris]

Hi Everyone,
Maybe someone could answer a couple quick questions for me. I'm wiring my new shop, and I was wondering...

1. How many 12 awg (120v/20a circuit) wires can be run through a 1" hole in a framing member?

2. Does a larger hole (say 1 1/8") change that number at all?

3. Does running the wires through several framing members (3 2x6's around a window) change the number at all?

I think the NEC addresses this specifically, but I don't have an actual copy.

Thanks for any help.

Dave

[Walter Hickman]

I am also wiring a new shop - slowly - about 6 months into the wiring - don't get much time to work on it. Almost through.

I called the inspector on this question - he told me two wires maximum in a hole. Probably some areas could be different with local regulations - that is for Knoxville, TN. Not sure about bigger hole

[Chris Friesen]

Around here I think the rule is pretty much as many wires as you can cram in there.

If they're running beside each other for significant distance (more than 24") then you have to worry about derating the ampacity based on the number of conductors but just for going through a framing member it shouldn't be a problem. Even at longer distances, the derating starts at the full ampacity of the conductor so you're still allowed 20A through a 12awg conductor with 90-degree insulation for up to 9 current-carrying conductors bundled together.

The 2008 NEC is available online at http://www.nfpa.org/onlinepreview/on....asp?id=7008SB.

[glenn bradley]

2 "romex" wires per hole is what I was told as well. Apparently there is no limit on the holes per stud however. My builder had so many holes in the plate above my original breaker box, there's more air than wood.

[Dave Norris]

Thanks guys. I was thinking two wires per hole, but the plate above my panel was going to look like Swiss cheese. I avoided that by taking some of the wires through the studs to the right and the left of the box.

Thanks again.

[Brad Sperr]

I've heard the two NM cables per hole rule of thumb that some inspectors use, but I don't think that's based on the NEC. I think Chris is correct that the real issue is derating, which doesn't become a limiting factor on a 20A circuit until you have 5 NM cables (or more than 9 current carrying conductors) running through a fireblocked hole (top plate or bottom plate) or running more than 24" together without maintaining adequate air space.