Question about Junction Box - Mounting, Stapling, etc.


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Old 12-26-16, 09:47 AM
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Question about Junction Box - Mounting, Stapling, etc.

I'm finally getting around to adding a junction box in my attic. I need it due to a box fill limitation when I add another smoke detector. I was thinking that I would use a 4" metal box. I'm going to remove the 12/3 that enters the existing old work box and move it to the new junction. From there, I would route a 12/3 to the old work box and a 12/3 to the new smoke detector. I asked some questions about this a while back, but I have a few more that I wanted to ask. I've also included a picture of the existing box. Thanks in advance for any advice.

1. What kind of screws (type/length) do I use to mount the new junction box?

2. Is there any issue with the metal box touching nails? On the joist, you can see that the nails stick out a bit and may touch the new junction box.

3. The run from the new junction box to the old work box will be so short that I'm not certain the best way to staple the NM. I would have preferred to just use the bottom knockout, but then there would be nowhere to secure the NM. If I mount the new junction behind the old work, I could use the knockout on the right side, staple it coming out, run it along the joist on the right and use another staple.

4. Is there any requirement for how the junction must be mounted? I wanted to install it against the joist that is behind the existing old work (the location where you see the NM emerge). I was originally going to use a new work NM box, but I thought that a metal one would be cleaner in this particular instance. I feel like a new work would have to be positioned in a strange way, since I'd have to secure it to the joist with nails.

 
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Old 12-26-16, 02:16 PM
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1) Screws of a length 1" or longer. I prefer Tek screws due to their larger head.
2) No issues. You are going to ground the metal box with the green screw and grounding wire anyway.
3) If you are using a metal box with hickeys, you will need to accommodate the protrusion of the screws in the back of the box. Normally they are mounted on the edge of a joist/rafter, not on the flat. If you want to mount it flat, then use a plain metal box with knock outs and no hickeys, and use strain relief's.. You have to secure the cable within 8" of the box and every 3' thereafter, so if your cable is only 6" long and a direct run in the same joist bay you won't necessarily need to secure it.
4) See 3
 
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Old 12-26-16, 07:44 PM
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Are you sure the existing cables are #12?
 
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Old 12-27-16, 11:17 AM
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Are you sure the existing cables are #12?
Yes, they are #12. It seems like all of the original wiring in my home is #12. It's not color-coded yellow, so I'm not sure when that started. It was built in the mid-80s. I don't know if it was common practice at the time to use #12 throughout.
 
 

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