Which boxes to use (box fill question)?

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Old 03-14-14, 08:58 AM
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Which boxes to use (box fill question)?

Hi everyone,

I've posted previously about my barn rewiring project and I have another question I'm hoping to get some help with - I can't figure out which metal electrical boxes to buy. I've been doing the box fill calculations and the ones I'm looking at on the Lowe's website don't seem big enough. I was hoping to use the rectangular handy boxes.

Here are a few of the different scenarios:
1. Daisy chained duplex receptacles on a 20A circuit (calculated that I need 15.75 cu. in.)
2. Daisy chained light switches on a 15A circuit that feed a branch of lights (calculated that I need 18 cu. in.)
3. Some of the light switches will be three-way switches and would have an extra wire (calculated that I need 20 cu. in.)

I guess my first question is...am I doing the calculations correctly? The second question is... can someone point me to the boxes that I should be using for this? I'm hoping to avoid going to 2-gang boxes for a single switch or duplex receptacle but if that's the only way then I understand.

Thanks again!
 
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Old 03-14-14, 10:24 AM
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I would just go with the deepest boxes you can fit in the wall.

Why are you looking at metal over plastic?
 
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Old 03-14-14, 10:43 AM
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I was hoping to use the rectangular handy boxes.
Handy boxes are not handy for anything other then one cable and one device.

I agree with PC, unless you are using a metallic wiring method, I would use plastic boxes.

If you are using metallic wiring, I would only use 4"x4" boxes with the proper mud ring for your wall finish. Although I like to use 1/8 deeper mud ring then the wall. (5/8 for 1/2" drywall) Gives you a little leeway.
 
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Old 03-14-14, 10:58 AM
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I'm looking at metal mostly because there are places where I will likely use conduit but I also like the look better in a barn of this age (silly, I know).

Maybe handy boxes was not the right word to use. I was really looking for single gang metal boxes that can accommodate that many wires. But the options seem pretty limited in size, so I'm not sure if I'm missing something.

If it matters, there aren't really any finished walls, so nearly everything will be mounted on studs / beams.

Any further advice or links would be much appreciated.

Thanks!
 
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Old 03-14-14, 11:10 AM
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No, you are correct calling them handy boxes. It is just they are so small that you really can't use them for much.

If you are doing exposed work use 4"x4" boxes (1 1/2" or 2 1/2" deep) and install single gang industrial covers on them. It is a good look, can fit lots of wires, and they are durable. We use them all the time in industrial spaces.
Example:
[ATTACH=CONFIG]28332[/ATTACH]
 
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Old 03-14-14, 11:58 AM
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Thanks Tolyn!

That seems like it'll work. Out of curiosity, if I were able to go without conduit and use plastic (cost seems a lot better) I have a couple of questions:

1. Are there plastic boxes that you can mount to the face of a wall / beam? I've only seen ones that seem to side-mount or that have to be recessed.

2. If I use a plastic box could I use a metal box cover? Are there any special grounding requirements if the cover is metal?

Thanks again!
 
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Old 03-14-14, 12:58 PM
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Plastic nail on boxes are really made for in a wall, not exposed, attached to the side of a stud. If you are looking for something that will attach to the surface you might want to look into this:
[ATTACH=CONFIG]28333[/ATTACH]

These are designed for PVC conduit which is attached with glue.

If you use a metal cover with a plastic box it will need to be grounded. Most cases it is better to use plastic with plastic, and metal with metal. Since you are doing everything on the surface, I would stick to metal.
 
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Old 03-14-14, 01:41 PM
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It seems like I need to pick and go one way or the other.

Sorry to have so many questions, but I'm trying to figure out a way to use plastic boxes that would still look okay. Would I be allowed to build a wooden box out from a finished wall which could house the plastic switch boxes? I'm trying to avoid cutting holes into the few walls that are finished because they're solid 19th century wood. I was thinking of something like this:

Name:  barn-3d-box.jpg
Views: 413
Size:  9.1 KB

Thank you again for all of the help!
 
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Old 03-14-14, 02:01 PM
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If your thinking of something like that, look into Wiremold. It is a better looking surface mounted raceway system.
 
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Old 03-14-14, 04:13 PM
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I guess what I really meant to ask is... is it legal to build out a wooden box around plastic electrical boxes?
 
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Old 03-14-14, 04:44 PM
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I don't see any reason that you can't. Just as long and the box is not recessed from the face of the wood.
 
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