How should I route wire around a box?

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Old 03-02-17, 10:44 AM
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How should I route wire around a box?

I am remodeling my bathroom and am bringing in a new 20 amp circuit.

I want the box on the bottom to contain the GFI outlet. The box on the top will house the connection for a hardwired lighted makeup mirror.

My issue is that I want to bypass the top box and bring the wire into the bottom box first and then into the top box. My issue is that I have very limited space. As you can see in the picture, the two boxes barely fit between the studs as it is.

I can't run the wire on the left stud and then bring it up because there will be a pocket door there. On the right stud it's the corner of the wall.

What are my options here?

Should I use a shallow box for the top box and run the wire behind it to the bottom box and then back up?

Can I run the sheathed wire through the top box down to the bottom box and then bring it back up to the top box?

Should I try running the wire down the adjoining wall and running it through the corner then bring it up?

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Old 03-02-17, 10:59 AM
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Mounting anything that close to a corner is problematic. Once the drywall is up it gets even tighter. What is the issue with moving the boxes the the right wall?

Yes, you can run the cable through the top box first. The only question would the the box fill calculation.
 
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Old 03-02-17, 11:10 AM
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What do you mean by "fill calculation"?
 
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Old 03-02-17, 11:16 AM
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Boxes are only listed for use with a certain amount of conductors. You will need to check to make sure there is enough room. Any device counts as two additional conductors. All grounds count adds one.
 

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Old 03-02-17, 11:29 AM
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Code specifies the required volume for electrical boxes based on the number and size of conductors that will run to or through a box, the number of devices in the box, and the presence of internal clamps in the box.

If you search for "box fill calculator" you will find many online calculators to help you determine if your boxes are large enough to do what you want. The volume of the box will be stamped somewhere in/on the box; xx cu inches.


Considering your upper box, you will have 2 conductors running through the box (the feed to the lower box) Grounds are counted separately. Then you will have 2 conductors spliced in the box (the connections to the mirror. Plus you have all the grounds, which count as one conductor. Single gang plastic boxes (plastic boxes in general) don't have internal clamps.

Assuming 12 ga wire, that works out to 11.3 cu in.
The bottom box will have 4 conductors spliced in the box, grounds, and 1 device. (Assuming you will pigtail the connections to the receptacle, pig tails don't count in the calculation). No clamps.

Assuming 12 ga wire, that works out to 15.8 cu inches.

So as long as your box volumes exceed those numbers, you are ok. Most standard (not shallow) single gang boxes are around 18 cu inches, so you should be ok.
 
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Old 03-02-17, 01:26 PM
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Plastic boxes will be stamped on the back with the number of conductors and sizes on the back.
 
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Old 03-02-17, 02:22 PM
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Just run the cable lower through the corner stud. There's no reason it has to be at any particular height.
 
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