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Old 10-26-2009, 10:59 AM   #1
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New Recepacles in a shallow wall


Hi,

I'm wiring a basement room that has only 1 1/2" from a concrete foundation wall to the finished surface. I believe it is 3/4 furring and 3/4" plaster. I would like to place 15 amp receptacles in these walls but there will not be enough space for even the shallowest boxes. Can I cut out the location for the boxes and then add a 1" thick spacer block to the finished wall with the same size cut out as the electrical box requires to allow for the depth? Then wire as usual?

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Old 10-26-2009, 12:27 PM   #2
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New Recepacles in a shallow wall


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Originally Posted by trosenda View Post
Hi,

I'm wiring a basement room that has only 1 1/2" from a concrete foundation wall to the finished surface. I believe it is 3/4 furring and 3/4" plaster. I would like to place 15 amp receptacles in these walls but there will not be enough space for even the shallowest boxes. Can I cut out the location for the boxes and then add a 1" thick spacer block to the finished wall with the same size cut out as the electrical box requires to allow for the depth? Then wire as usual?
I would seriously look into using surface wiring (Wiremold) to do this.

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Old 10-26-2009, 12:33 PM   #3
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New Recepacles in a shallow wall


If you're recommending surface mounting is that because my original suggestion is not an appropriate solution? or is surface mounting just the usual way of solving such a problem?
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Old 10-26-2009, 12:55 PM   #4
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New Recepacles in a shallow wall


Since the walls are already finished, I think the Wiremold would be an easier and better looking alternative. You could have a difficult time fishing wires behind the plaster (are the furring strips vertical or horizontal?) and the 1" blocks would look weird.

If you really don't like Wiremold, and don't mind fishing the wire, you could use 4x4x1.25 square boxes with 1/8" mudrings and patch the cutout area, leaving only the mudring opening.
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Old 10-26-2009, 01:09 PM   #5
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New Recepacles in a shallow wall


One small box I know of is only 8 cu inches & 1.25" deep
14g wire = 2 per hot plus 2 for device + 2 for ground
So it is only rated for a wire going into the box



The next step up for 2 wires is rated at 18 cu inches & is 2 7/8" deep
Its rated for up to (2) wires - 14g or 12g
2 for each hot x 4, 2 for device, 2 for grounds = 12 cu inches
12g would be 2.25 x4, plus another 4.5 = 14.5 cu inches

That would stick out about 1.5"
You could cut out a piece of wood block and have it spaced out as you say
Could be a PIA to fish the wires
But I think I'd prefer that over wire mold
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Old 10-26-2009, 01:53 PM   #6
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New Recepacles in a shallow wall


The box posted by SD would need to have 10 cubic inches before it could be used. Six ci for the cable and 4ci for the device, assuming #14 wire.
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Old 10-26-2009, 01:58 PM   #7
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New Recepacles in a shallow wall


Thank you for the clarification on junction box volume requirements Jim. Is there a good resource or simple formula for calculating box volome requirements to meet NEC given a number of conductors and their size entering the box as well as the device?
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Old 10-26-2009, 02:04 PM   #8
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New Recepacles in a shallow wall


Yup he's right...device (outlet) counts as 2 current carrying conductors...not 2 cu inches
1 per receptacle ?
I have only used it as a switch box due to a pocket door
Switch counts as 1 from what I have read ? (nope I'm wrong - can't even read what I copied & pasted here )

The Chart Says That (NEC Article 314.16.B):
14 Awg. = 2 Cu. In. per conductor,
12 Awg. = 2.25 Cu. In. per conductor
10 Awg. = 2.5 Cu. In. per conductor
8 Awg. = 3 Cu. In. per conductor
6 Awg. = 5 Cu. In. per current carrying conductor counted.

Calculating Current Carrying Conductors

If you are using all conductors of the same size in your box, then you must count the number of current carrying conductors [all colors including white but not counting green or bare] entering your box. Also do not count conductors that neither enters your box nor leaves your box. [pigtails only, these are ignored].
Now add to your number of current carrying conductor list, by counting all of the grounding conductors as one conductor [green or bare], no matter how many grounding conductors, just add the one current carrying conductor to your total number of current carrying conductor list. Remember that all grounding conductors [green or bare] must be counted as a total of one current carrying conductor. NEC Article 314.16.B.5
Clamps are also counted the same as grounding conductors, one current carrying conductor must be added for the total of all clamps found in the box. All clamps found within your box that are entering the box at least , no matter how many, count as a total of one current carrying conductor, only, for all of these clamps. Now add this one conductor count to your total number of current carrying conductor list, if any of these clamps are present. NEC Article 314.16.B.2 A single gang plastic or fiber box will have no clamps to consider. They are exempt from a clamp requirement. NEC Article 314.17.C.Exception

Devices yokes must count as 2 conductors for each device. Count the number of devices {switches or receptacles}. Multiply the total number of devices times 2. The answer from multiplying the total number of devices by the 2 is the total number of current carrying conductors you must add to your total number of current carrying conductor list. NEC Article 314.16.B.4
Now this final total of your current carrying conductor list is the answer to the total number of current carrying conductors installed in your box.
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Old 10-26-2009, 02:12 PM   #9
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New Recepacles in a shallow wall


switch counts as two conductors also.
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Old 10-26-2009, 02:27 PM   #10
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New Recepacles in a shallow wall


A device like a switch or a receptacle counts as 2 wire volumes of the largest conductor it is connected to. Even a GFI only counts as 2 volumes.

Scuba Dave has provided a very comprehensive chart for conductor fill calculations.
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Old 10-26-2009, 04:27 PM   #11
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New Recepacles in a shallow wall


The closest thing I have found is a carlon b117rsw. It is 17 cu inches, but only 2 inches deep.
Still deeper then you want or need.
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Old 10-26-2009, 07:27 PM   #12
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New Recepacles in a shallow wall


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Can I cut out the location for the boxes and then add a 1" thick spacer block to the finished wall with the same size cut out as the electrical box requires to allow for the depth?
I suppose.....but it would look like hell. Even though they are "too small" , I would just use the shallow boxes pictured. There is really plenty of room in them for one cable and a device.

I have also seen a box like that that was wider and had enclosed space off to one side to give it more cubic inches.

If you truely have a full 1.5" you can probably use a standard shallow 4 square box with a flat mud ring You will of course have to tape the sides of the mud ring or use double duplexes.
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Old 10-26-2009, 08:30 PM   #13
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New Recepacles in a shallow wall


Use a wiremold extension box on the extra shallow box shown.

The catalog numbers are: 5751 (buff) V5751 (ivory) or 5751-WH (white). You can conceal the wiring, and the box will stick out about an inch as originally stipulated.

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Last edited by kbsparky; 10-26-2009 at 08:35 PM. Reason: Added photo
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Old 10-27-2009, 10:28 AM   #14
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New Recepacles in a shallow wall


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Use a wiremold extension box on the extra shallow box shown.

The catalog numbers are: 5751 (buff) V5751 (ivory) or 5751-WH (white). You can conceal the wiring, and the box will stick out about an inch as originally stipulated.

Are you suggesting a metal extension on a plastic box?
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Old 10-27-2009, 11:12 AM   #15
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New Recepacles in a shallow wall


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Are you suggesting a metal extension on a plastic box?
Yes - that is exactly what he is saying

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