Not enough depth for junction boxes

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  #1  
Old 12-14-05, 06:10 PM
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Not enough depth for junction boxes

I am relocating a 3-way switch, and an electrical outlet. I have already run the cables and cut away the drywall on the wall I was planning to put these on. Unfortunatley, I only have about 1-1/2" between the drywall and the block wall behind it. The junction boxes I need to use are way deeper than that,(approx. 3-1/2") and therefore will not end up sitting flush against the wall. Do they make more shallow junction boxes, for these circumstances. Are there any other suggestions, or should I just pick a different wall??

Thanks.
 
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  #2  
Old 12-14-05, 06:15 PM
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junction boxes

How many cables or wires will be in the box? Are you combining the receptacle with the switch, or will they be in different boxes? There are shallow boxes, but they have a reduced capacity, and you will need to calculate the number of wires, excluding the grounding wire that will be in the box.
 
  #3  
Old 12-14-05, 06:31 PM
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These will be in seperate boxes. The 3-way box will actually hold two different switches and have 3 different cables coming into it with 2 wires, 3 wires, and 3 wires repectively not counting the grounds. The outlet box will have two cables coming into it with 2 wires each...excluding the ground.
 
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Old 12-14-05, 07:26 PM
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Originally Posted by tool73
These will be in seperate boxes. The 3-way box will actually hold two different switches and have 3 different cables coming into it with 2 wires, 3 wires, and 3 wires repectively not counting the grounds. The outlet box will have two cables coming into it with 2 wires each...excluding the ground.
What is the AWG size of the conductors: 12 or 14? You need 2.0 cubic inches per #14, 2.25" per #12, and for other sizes see NEC 370-16 (b), which also outlines allowances for clamps, yokes. For example, if your largest connected wire is #14, you must allow 4.00" per switch.

I am not an electrician but here are my figures:

For the switch box, if all your wires are the same size and all are spliced or connected:
2 wires + 3 wires + 3 wires = 8 wires * 1 volume per wire = 8 volumes
2 switches * 2 volumes per switch = 4 volumes
1 ground * 1 volume for all grounds = 1 volume

Assuming you have #14:
8*2.00 = 16"
4*2.00 = 8"
1*2.00 = 2"

Then add them up:
16+8+2 = 26 cubic inches.

Ideally then looking at NEC 370-16(a) you would use a 4 x 2-1/8" box which has a volume of 30.3 cubic inches.

Since you don't have room how about a 4 x 1-1/2" box, volume 21.0 inches, plus a rated cover or mud ring with a volume of 5 inches or better?

If that's too crowded, you could put a relatively shallow wiremold box on top of the 4 square box.

You could also use a 4-11/16 x 1-1/2 which has a volume of 29.5 cu. in. You may not find a good selection of this size box and mud rings at the big box, but the electrical supply house should have them.
 

Last edited by ArgMeMatey; 12-14-05 at 07:37 PM. Reason: Math error
  #5  
Old 12-14-05, 07:57 PM
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ArgMeMatey,

You and I were on the same page and doing the same math...

A 4x4x1.5 metal box is 21 cu in.

Looking at two mud rings I happen to have in my supply box...
A mud ring for two devices adds 7.3 cu in to the box, for 28.3 cu in.
A mud ring for one device adds 5.5 cu in to the box, for 26.5 cu in.

...Now, that one device ring looked more like a 5/8" deep ring rather than 1/2", so that number may be slightly high.


In the case that the switch box has #12 wire, the fill goes up to 13*2.25, for 29.25 cu in, so the box would still not be quite big enough, even with the two device mud ring.

Even if you have #14 wire for this box, I'd see if there was any way I could redesign these switch circuits to eliminate one cable from this box...It's gonna be full as it is.

BTW: Remember that you must tie all your grounds together in the box, tie them to the box, and tie them to each switch.
 
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Old 12-14-05, 08:01 PM
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Originally Posted by ArgMeMatey
You could also use a 4-11/16 x 1-1/2 which has a volume of 29.5 cu. in. You may not find a good selection of this size box and mud rings at the big box, but the electrical supply house should have them.

Now, that would do...

The local big box store with all the orange has the 4-11/16" boxes, but I haven't seen any 4-11/16" mud rings there. If you get one of these boxes, be sure to get the one with the 1/2 & 3/4 knockouts rather than the one with the 1" and 1 1/4" knockouts.

...and don't forget the romex connectors.
 
  #7  
Old 12-14-05, 09:04 PM
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Thanks for the assistance, fella's. You guys are the best! FYI, the wires are 14/2, and I was incorrect before. There is only ONE of these that will go into the j-box for the outlet.
Thanks again.
 
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