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Dave Ermeling · May 18, 2008, 08:27 AM

I'm finishing my basement and in process of wiring it. I was wondering if the NEC code specified a maximum number of 12-3 or 14-3 wires coming into an outlet or switch box. I have heard two different opinions on this. One opinion was that I could only run two wires into a standard single gang outlet/switch box and 4 into a deep box. The other opinion was that I could run as many wires in as there were holes or slots for wiring built into the box. So if I had a Carlon single gang box which has 2 openings in the top and 2 in the bottom, I could run 4 wires in. Whereas a 2 gang switch box has 4 opening on top and 4 on bottom meaning I could run 8 wires in. Any help would be apprciated. I'm wanting to run another couple wires into a double gang box where I now have 3 wires in already.
Thanks,
Dave

Dave Ermeling · May 18, 2008, 08:52 AM

After reading another post about the issue, it looks like the printing inside the box says, 16/14, 14/12, 12/10. Does this mean I can run 5 pulls of 14/3 w/ gnd into the box(15 total wires)? Or 16 pulls of 14/3 w. gnd? (seems like an aweful lot.)

stanfortyman · May 18, 2008, 08:58 AM

That is the number of conductors. This is not as simple as it seems.

#14 has a volume allowance of 2 cu/in
#12 has a volume allowance of 2.25 cu/in

Each CCC (current carrying conductor), basically anything except a ground, is ONE conductor.
ALL the grounds combined count as ONE conductor.
EACH device mounted in a box is counted as TWO conductors.
ALL internal cable clamps combined inside the box are counted as ONE conductor.
These are all based on the largest conductor in the box.

So a single gang box with a receptacle and two clamps, and two 14/2 cables, would have a volume of 8 conductors, or 16 cu/in.

Dave Ermeling · May 18, 2008, 09:19 AM

Stanfortyman, when you say "cable clamps" what are you referring to? Wire nuts?

stanfortyman · May 18, 2008, 09:55 AM

No, the clamps that hold the cables in the back of the box.
Most metal device boxes come with them. Only some plastic boxes do.
Most plastic boxes have molded in clamps which don't count.

Dave Ermeling · May 18, 2008, 09:59 AM

OK, I gotcha. I'm using all plastic Carlon boxes with the clamps built into the top and bottom of the box. It all seems more complicated than it has to be. Thanks for your advice.

stanfortyman · May 18, 2008, 10:08 AM

No problem.
I guess when you do this stuff every day you don't even think about it anymore.