Plastic boxes, holes in studs

Most of the plastic electrical boxes I'm using are made by Carlon; a few are made by others. The Carlon boxes have "tabs" in the back that apparently you break out to run the cable into the box. The other boxes have similar tabs, but they're more of a clamp type... you push the cable in and the tension of the tab holds it in place.

Am I correct that the Carlon tabs break out? I thought that it was mandatory that the cable be clamped in some fashion where it enters the box, but if you break the tab out, there's nothing clamping the cable.

Did that make sense? Am I doing it right?

A separate question--I think I've had this answered already, but just to be sure, I'll ask again. Can I run more than one cable through a single hole in a stud? My holes are 3/4 inch, and there are just a few places where I could have three cables in one hole, and a few more places where I'll have two.

It wouldn't be a big deal to drill more holes, but I figure the less holes, the better.

I'm ready to run my cable, and I want to make sure I'm doing it right. I appreciate any responses to the questions above, as well as any other suggestions. Thanks...

Brian

 

A follow-up to my own post... I think I just read on Carlon's website that clamps are not necessary in single-gang boxes (which they all are). Is this true? Why?

 

Don't break out those plastic tabs. Just push the cable through them. They grip the cable a bit. Those tabs, combined with that staple within 8 inches of the box, serve to secure the cable adequately.

Yes, you can run two or three cables through a 3/4" hole in a stud, assuming they fit comfortably. But there's nothing wrong with drilling multiple holes either.

 

John,

I think I understand what you're saying, but I don't these tabs are meant to work like that. Carlson actually refers to them as "knockouts." they're connected at two points, and if you break one of them (you have to to get the cable through), it just hangs there. I have since found a second website which confirms that you don't need cable clamps in a single gang box (http://www.familyhandyman.com/200103...s/w/page5.html), so I'd have to think that the tabs are indeed knockouts and are intended to be removed.

As always, thanks for the help, and I appreciate your input...

Brian

 

You need clamps in every and any box. There is no exception in the NEC for this. The plastic tabs are a poor, but acceptable, cable clamp. I would not use plastic boxes if they where free. They are a cheap substitute for a metal box.

 

Brian, that staple within 8" of the box will secure the cable adequately. Make it snug but not tight enough to damage the cable.

 

Brian:

Yes you are correct.....There is an exception in the code book to allow this.
In single gang boxes that are no larger then 2 1/4" x 4" mounted in walls or ceiling, and the cable is fastened within 8", and the sheath extends in to the box at least 1/4". then you do not need to secure the cable to the box.

If the the box is something other then a single gang box then yes the cable must be secured to the box.

 

aphares is correct under 314.7(C) Exception. Plastic boxes are still a lousy substitute for metal boxes.

 

314.17(C) in the 2002