Switch boxes nailed through the back???

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  #1  
Old 10-27-14, 12:41 PM
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Switch boxes nailed through the back???

OK for the gurus here,

I have a 1935 house, most walls seem to be 3/8" plaster on 3/8" rock lath. Wiring is BX with 3x2 switch boxes. Hard to say if the wiring is original or added later. It seems like the switch boxes are against studs based on my stud finder's beeps.

There's a few places where I may want to pull out one of these switch boxes to rewire/split circuits, so I wanted to figure out how they're mounted and more importantly how to reattach (or replace with new metal boxes since I'm not getting rid of the BX entirely and also using modern MC). I'd prefer to reattach in a "new work" fashion without resorting to plaster ears, Madison straps, etc. Arlington F101S boxes are an option if I can find them.

When I removed an outlet, to install a GFCI (three prong update per 406.4(d)(4)), I looked in the box to see how it attached. I didn't see any sign of nails or rivets in the side, plaster ears securing to lath (seen elsewhere in the house), nails across the back or anything like that.

I did see two bumps in the back of the box that looked like nail heads. Did they nail through the back into the clapboard and backing on the other side of the wall? Did I miss something else?
 
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Old 10-27-14, 01:51 PM
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There should be no fasteners inside the box to where they can work loose and become in contact with the wiring. BUT, who is to say it was a retrofit by someone in the past 70 years. They probably nailed into a backer board of some sorts rather than into the clapboard.
 
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Old 10-27-14, 06:41 PM
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A difficulty with fastening a box by its back is getting the front to be lined up with the wall surface.

You could be lucky and it comes out correctly, or you can use shims that might involve a lot of trial and error.

Many boxes notably 4x4 square boxes do not have fins to nail to the wall so fasteners are commonly inserted from the inside.
 
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Old 10-28-14, 04:07 AM
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Many boxes notably 4x4 square boxes do not have fins to nail to the wall so fasteners are commonly inserted from the inside.
Correct. I was thinking more of using bad fasteners such as roofing nails, etc. rather than screws which would not tend to back out. My emphasis should have been on the fasteners themselves.
 
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