plastic or metal boxes?

[davidj]

I'm just about to start on the electrical in our 20x30.  A friend recommended using 4" metal boxes with mud rings everywhere - more solid and you don't have to worry about the depth of the finish surface.  This seems appealing - not quite the cheapest route but it delays some decisions and allows more changes later (e.g. adding another receptacle is easy).  Any reason why not to take this approach?  Do the mud rings work fine with e.g. T&G paneling? I was thinking of using flat 2x6's behind each box which should make them really solid and allow for extra blocking to support the T&G once we've decided whether it's going horizontal or vertical (or turned into sheetrock because we spent all of the money on electrical boxes :->).

[MikeT]

As usual, I will let the better answers come from others, but here is my take and how I approached things:

Metal vs Plastic:  plastic is cheaper and acceptable.  With plastic, you tie all the grounds together in the box to one another.  With metal, you tie the grounds to the box. 

With respect to the boxes and mud rings, I think you have that choice with plastic too.  Using the boxes for two receptacles/switches will give you more room for wiring.  I think that adding an outlet later is more difficult than just the size of the box because you would be running wire through finished walls, but that is another issue.

On my project, I used the plastic boxes almost everywhere.  In addition to being 5x cheaper, you do not have to buy extra strain relief like you do with the metal boxes.  With the plastic boxes, wires have to be secured to a stud with a staple within 8" (I think that is right), and with the metal boxes, you get 12" (again, I think).

Now for the corrections.....

[muldoon]

metal is necessary for outdoor installations because the weather and the uv will breakdown the plastic.  inside however you do not need the metal and plastic will suffice.  personally I prefer the plastic inside because they are not conductors and you dont have to worry about something becoming hot in a worst case situation when that elect tape falls off and the wire nut loosens form cold/hot expansion after 10 years in the wall.    Either is fine, the plastic is my personal preference inside. 

you should be securing the wires to studs with the proper attachment hardware, not really staples.  the staples pinch the wire, and its pretty easy to puncture if your not careful.  not exactly a correction, but if someone is about to start this effort - they probably should get the right stuff for it. 

[MountainDon]

Plastic meets code when used with Romex or NM, is less expensive and in my book easier to work with. BUT, there is one thing I do not like about them. It is possible for an installer to tighten the recetacle/switch screws too tightly and strip the plastic threads. There must have been a gorilla wiring my house because I have had several with problems. BUT I have had no problems with any that I have installed. I used plastic in our cabin build.

I've never used mud rings so have no comment on them.

I spaced my boxes to suit the type of wall covering, 5/8" drywall or the slightly thicker T&G.

When it is stated that metal is necessary for outdoors that is only necessary if the boxes are exposed. An outlet in an exterior wall can be fitted to a plastic box. You would of course use a gasketed outdoor cover plate.

Staples made for the purpose of securing Romex or NM wiring have a flat plastic or metal plate to prevent cutting into the wiring.

[rocking23nf]

metal boxes outdoors? usually you use plastic boxes outdoors with waterproof seals on it. during my years as an electrician I never once saw or used an outdoor box that was metal. Now i did do commercial work, but I would think the theory would be the same. Its the same with conduit, once the line reaches an outer wall, you use a LB connector and switch to Plastic pipe.

In your house, I would use metal boxes, they are cheap, they dont strip out. They last forever.  Only 1 wire in a box needs to wrapped around the ground screw, the rest would splice onto the end of the ground.

Also if you are using metal recepticals, they mount really easy with 2 nails, one at top, one at bottom.

[MountainDon]

I have some metal, surface mount boxes for outdoors weather proof outlets around the house. Some sort of cast metal.  They are 25 years old.  Now that you mention it though I have also used plastic Carlon ones in recent years. I forgot about those.  


This one states it is aluminum though


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