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# How many wires can a box hold?

#1
04-22-05, 03:58 AM
Member
Join Date: Dec 2004
Posts: 41
How many wires can a box hold?

I have a 32 cu-in double gang box (the deepest box I can get from HomeDepot) that will hold 2 3-way switchs, now that there are 6 cables entering this box:

2 12/3 cables for the 3 way switches
2 12/2 cables going to the lights controled by these switches
1 12/2 cable for power feed
1 12/2 cable brings power to the receptacle box underneath this box

My questions is can all these wires fit in the box? Thanks.

#2
04-22-05, 04:08 AM
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Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
By my calculations you have exceeded box fill requirements.

My suggestion is to run the wiring differently.

#3
04-22-05, 04:23 AM
Member
Join Date: Dec 2004
Posts: 41
Can you please give me some more details on how the box fill requirement is calculated? Thanks.

Originally Posted by racraft
By my calculations you have exceeded box fill requirements.

My suggestion is to run the wiring differently.

#4
04-22-05, 04:25 AM
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,984
You would have the equivalent of 19 wires in this box. Each switch counts as 2 conductors and the ground would count once.

19 x 2.25 = 42.75 cu. inches.

#5
04-22-05, 08:38 AM
Member
Join Date: Apr 2005
Location: SE Pennsylvania
Posts: 19
The technical info for volume calcs can be seen here
As someone who just had the same problem, I will tell you what the experts here at the forum suggested, if you can make it work....
Run power to lights first, then 12/2 to each of your other 3-way switches - then a single 12/3 to each 3-way at your referenced box is all you will need to provide a loop between each of the two sets of 3-ways.
One item that folks seemed to have different opinions on was whether to add a conductor count for the internal clamps (even though they're skimpy) that are present in the 2-gang box. Since the manufacturer's info says to count it, I did. This would bring your total conductor count to 20.

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