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Discussion Starter · #1 ·
Hello

I'm considering installing a 3 gang metal box, flush to wooden studs. With a 1/2" depth 2 gang box extension ring.

So the finished wall will have a 2 gangs, but actually 3 behind the wall. The purpose is for box capacity. I know this will technically work, assuming the extension fits, but are there any code issues I should be worried about ?

I plan on having a multi light switch 2 pole (1 gang) on the left, and a LED dimmer on the right. So I could do with the extra space back there.

Some photos of the equipment i'm installing attached.

Thanks in Advance !
 

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Naildriver
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What are your plans for the third bay on the box? You can't leave it uncovered.
 
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Usually Confused
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Chandler asks a good question and I don't know what the Code says about simply drywalling over the third box. I suppose you could put a blank plate over it and maybe auger out the back of the drywall where the screws will interfere.
You could also build a two-gang box and use a side box extender for the extra space.


 

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I have seen metal three gang - two device mud rings. You won't find them at the big box stores but may find it at electrical supply stores. I installed a five gang - three device mud ring over a five gang box a few years ago. The mud ring itself is as wide as the box but the raised opening is smaller.
 

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Discussion Starter · #6 ·
What are your plans for the third bay on the box? You can't leave it uncovered.
The only cover for the 3rd bay would be drywall, that's the part i'm not sure is allowed by code. I could put a flush/flat metal cover over it. The 3rd bay would be like a large side box extender.

Essentially there will be 3 x 3 way light switches. one is a 3 way dimmer so I believe I'll end up with 12 x 14guage wires including ground.
 

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Discussion Starter · #8 ·
Only drawback to that cover would be that it will not fit properly on a three gang masonry box as pictured above.
Thanks- right i'm not sure what type of box is needed for that mud-ring. definitely the cleanest solution, but doesn't appear it would be a standard "switch" box.
 

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Consider going with either a 4-SDW-FB-SPL or a 5-SDW-FB-SPL and you'll have 30.3 in³ and 40 in³ respectively. That will allow you to pick any rise mud ring to flush up with your wall finish.

Those boxes are designed to mount with the bracket flush with the wall stud. Code allows 13 #12 in the 4s deep box and 18 in the 5s deep box. The mud ring will add a little more in³ so figure out which box is going to meet your needs, if either, and you'll be using what most electricians would for your situation. Leave the SPL off if you want all 1/2" ko's.
 
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Use deep boxes. They are 3.5 inches deep. How much room in a box do you think you need to house a couple switches? Visit your local Electrical supply house and they will show you all kinds of things that will suit your needs.
 

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Discussion Starter · #11 ·
Consider going with either a 4-SDW-FB-SPL or a 5-SDW-FB-SPL and you'll have 30.3 in³ and 40 in³ respectively. That will allow you to pick any rise mud ring to flush up with your wall finish.

Those boxes are designed to mount with the bracket flush with the wall stud. Code allows 13 #12 in the 4s deep box and 18 in the 5s deep box. The mud ring will add a little more in³ so figure out which box is going to meet your needs, if either, and you'll be using what most electricians would for your situation. Leave the SPL off if you want all 1/2" ko's.
Yes this is a much better way of dealing with it. I went with your plan, even found the stud mount for those boxes. Just hope it will fit 12 wires. I went with the 40 cu one.

Thanks for your help, exactly what I needed.
 

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How many 12/2 NM cables are you needing to run into the box or are you running conduit to it?
 

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Discussion Starter · #13 ·
How many 12/2 NM cables are you needing to run into the box or are you running conduit to it?
No conduit. It’s a regular wood stud wall. One gang is an LED dimmer / multi location master.
Other gang are two x 2 pole switches (multi location).

I haven’t figured out the wiring exactly yet but I’ll be using 14 gauge. Because multi location I may need some 14/3 - but total core count will be around 12.
 

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The code allows for 21 #14 wires in that box. You can easily tolerate as many as eight 14/2 cables into that box and have room left over since that isn't including the extra volume created by the mud ring. I doubt you need all that! :wink2:
 

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Discussion Starter · #16 ·
2 x 3 way switches (one gang)

Second gang will be a “3 way dimmer” - technically a master multi-location dimmer for recessed cans.
 

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Well then go with the deeper metal 4x4 two gang box and you can even put a metal extension on it with a mud ring (mud rings have stamped on them Cubic Inches). Just be sure your wall cavity depth can handle it. You should have plenty of room then.


Here is a box fill calculator for you if it helps that you can follow and get more familiar with.


Box fill calculator. Use this for this project and for your future needs.
 
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