How to secure outlet boxes to studs when running surface mount EMT

Question

My workshop is not finished (i.e. walls are open) and I plan to keep it that way. My plan is to surface mount the EMT and outlet boxes to the wall studs as opposed to running EMT through the studs. But I wonder if this is a bad idea for the following reasons:

1. Some of the outlet boxes (mainly 1-gang) look to have no back holes through which I can run screws to secure to the studs. If there are holes, they are off center, which means they will get a lot of torque when plugging/unplugging.

2. Some 2-gang boxes have center holes in the back, but I think the boxes will wiggle a lot with just two screws right in the middle. Again, there will be a lot of torque on these screws.

I think I need a better way of securing the boxes to the studs, but I just don't see it right now. Are the problems I listed above real problems and is there a better way of doing this?

Answer 1

First, consider using 2-gang boxes even when you don't really need them. They have more practical splicing space, and easily accommodate GFCIs for instance (whereas they're a very tight fit in a 1-gang Handy-Box).

You don't need to use the fancy $4-6 cast boxes intended for outdoors. All you need (not outdoors) is the common 99 cent drawn or welded boxes (I prefer drawn).

The 4x4 and 4-11/16" 2-gang boxes have holes on the center axis. The 1-gang Handy-boxes do not, but they're still close enough to center that you should be able to mount them on a 2x4. But if they don't, you are welcome to drill mounting holes yourself, just push nice-n-hard and keep your speed up, so the drill is making curls instead of powder.

If you're worried about being near the edge of the wood and splitting it, pre-drill the hole and use a drywall screw etc., I prefer deck screws with Torx or Robertson.

Don't accidentally use the #10-32 tapped ground screw hole as a mounting screw.

Answer 2

Don't look at device boxes, which are one gang, two gang, etc. Handy boxes are OK for a switch or etc. but not what I'd use here. I wouldn't want plastic faceplates for shop use, even though the nylon ones are pretty durable.

You want 4x4 boxes

and raised industrial covers

The 4x4 (aka 4-square) boxes will have the holes where you want them. You can get raised covers for a single duplex receptacle, two duplex receptacles, single round receptacles, GFCI receptacles, just about anything you want.

They look good, and they are extremely durable.

Answer 3

In my layout (I've gone all conduit or MC-lite ala Chicago after due consideration of the local rural fire department's response time and rodent teeth) 1-gang boxes are practically useless just due to wire fill (cubic inch) issues. So I don't own any, but my recollection is most are optimized for side mounting to studs, which is a bit inconvenient for running conduit into them. If there are at least two holes in the back, I wouldn't worry about them being off-center.

The vast majority of my boxes are 4x4, which happen to have plenty of back holes. I slap on whatever mud ring or exposed work cover I need for the face depending what's in them. A few are the far more expensive but capacious 4-11/16" squares where fill requires. So for a single outlet or switch in exposed work, I'd use a 4x4x1.5 box with an exposed work cover, either single for the device or a double that includes blanking plates for the device you are not installing right now, if expansion might happen.

For my general outlet runs I wanted multiple circuits available at most locations, and in part due to wire fill requirements I hunted around for an affordable and capacious box, and landed on 5-gang "masonry" boxes - those have 10 mounting holes and two ground screw holes in the back, and two mounting holes on each side. I'm not quite sure why they happen to be the sweet spot in terms of capacity to cost, but they were when I was shopping.