Wall Box Capacity


Old 03-18-05, 08:04 PM
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Wall Box Capacity

How many wires can I run into a single-gang wall box? And what about double-gang? Our basement has some double-gang boxes with 8 wires (or 4 cables) in it already and I was hoping to add some outlets to it.

If I can't add on, can I just put a junction box along 1 of the cable runs somewhere?
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Old 03-18-05, 08:18 PM
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Several important pieces of data are necessary to answer your question.
  1. What size is the wire? Is it 12-gauge or 14-gauge?
  2. How big is the box? The size of each box, in cubic inches, is embossed or stamped into the back of the box. If you can't find this information on the box, then measure the box for us. Tell us height, width and depth.
  3. Do the cables have grounding wires too?
  4. Is the box metal or plastic?
Adding a junction box along one of the cable runs may be a problem since it is unlikely the cable has sufficient slack to allow this, and still have enough wire to make connections safely.
Old 03-19-05, 04:51 AM
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1. 14-guage
2. 18 CU. IN.
3. Yes
4. Plastic

I noticed it says


embossed on the box also. Does that mean I can run nine 14-guage wires? Not counting ground?
Old 03-19-05, 07:44 AM
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The 9 #14 would count the ground also. Any device placed into the box would count as 2 of the 9 also.

Ex. 2 cables of 14-2 with a receptacle = 7 wires.

Last edited by John Nelson; 03-19-05 at 08:53 AM. Reason: correct a typo
Old 03-19-05, 08:49 AM
Join Date: Sep 2000
Location: United States
Posts: 18,497
I never buy 18-cubic-inch boxes if a larger box will fix in the space. 18-cubic-inch boxes are just too darn small.

An 18-cubic-inch plastic box can have four 14/2 cables in it if there is no receptacle or switch in the box. If there is a receptacle or switch, it can only have three.

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