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 crater13bravo 07-30-2012 06:04 PM

Receptacle Box Capacity

Hello all! I have a question that I can't seem to find the answer to. I am wiring a bedroom and am trying to determine if I can wire a receptacle and junction out to another receptacle box and an exterior motion light. Basically, I want to feed a deep single gang receptacle box for the receptacle. My question is can I then junction out to another receptacle down the wall about 8 feet, but also junction up to an exterior motion light? Can all of these wires be in a deep box? I do not understand how the NEC calculates number of conductors and air space. I understand it, but it doesn't satisfy me with my question of whether I can do this or not.

This is in a bedroom that is in the corner of my house adjacent to the front sidewalk.

 MisterZ 07-30-2012 06:13 PM

Calculations based on cubic inches of box and wire guage. NEC Table 314.16(b)

22.8 cu in. non-metallic box using 14/2 wire = 11 conductors.
count 2 for wiring device, 1 for each colored wires, 1 for clamps (if needed), all grounds combined =1

if im not mistaken;)

 electures 07-30-2012 08:06 PM

Plastic or metal? Wire size?

 crater13bravo 07-30-2012 08:14 PM

Metal 2x3x3-1/2. 12-2 with ground

 MisterZ 07-30-2012 08:27 PM

I believe it is 8 conductors.
2 for thedevice box - 1 for each insulated wire - 1 for all grounds

 electures 07-30-2012 08:49 PM

Quote:
 Originally Posted by crater13bravo Metal 2x3x3-1/2. 12-2 with ground
Your box is not big enough.
3 whites
3 blacks
1 all grounds
2 device
1 clamps

10 conductors

Box is rated for 8 conductors

 theatretch85 07-30-2012 10:57 PM

Quote:
 Originally Posted by electures (Post 977987) Your box is not big enough. 3 whites 3 blacks 1 all grounds 2 device 1 clamps 10 conductors Box is rated for 8 conductors
12 gauge wire is a factor of 2.25, so given all the numbers above, you need a box with a minimum of 22.5 cu in.

 MisterZ 07-30-2012 11:08 PM

Switch to plastic. They are a bit larger, and no need to ground the box;)

 electures 07-30-2012 11:12 PM

Quote:
 Originally Posted by MisterZ Switch to plastic. They are a bit larger, and no need to ground the box;)
The deep plastic box is 20,5 cu in. Since there are no clamps it will work.

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