What is the best way to mount an electrical box in concrete block to prevent blow-out when the column of blocks is filled with concrete?
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You could bed it in mortar in advance. Seal all of the unused openings and other holes with caulk. Use 'leak-tight' or glued conduit fittings.
Alternately, you could bolt the face of the box to a scrap of wood (somewhat larger than the hole for the box), then screw the board to the block wall to create a dam.
For either of these, the 'blue' PVC boxes are not the best choice, due to their potential for 'racking' [been there- whoops!]. Grey [exterior type] PVC or the brown 'bake-o-lite' boxes would be better. Not sure if the aluminum ones will hold up long term. I embedded an aluminum one in mortar years ago, and it has been fine. Steel just seems to be asking for troubles...
Best of luck.
I would run PVC conduit into a standard mason's box , Galvanized steel with the device mounting tabs on the inside of the box, with a standard female adapter. Seal openings in the box with duct tape.
Mount the box, face to the board, with a piece of wire fed through two holes in the back of the box and either around a 1 by 2 or, if you busted the hole a bit oversized and want to keep the concrete in the wall, a piece of plywood. Snug the wire up tight to keep the face of the box hard against the wood if using the ply. You could use tape to seal the interface but it isn't usually necessary.
Mount the board or plywood to the wall, holding the box in its final position, with a couple of short Tapcons. Pour the concrete and after setting up cut the wire and remove the board. The two wires coming out of the back of the box are easiest cut with nippers and the small stubs pounded flat so they don't damage any insulation.
I wouldn't run cable to this assembly as it makes repairs a PITA. If the rest of the house is wired in NM, Romex, sleeve the cable down the conduit you stubbed up above the concrete. If the house is run in flex or conduit just hook it up normally. Any problems later and you can yank out the cable, mount a box if needed, and run new in.
Though, if you are covered by the code police then you might want to check if busting a hole in the block is allowed. NOT allowed here on exterior walls.
Interesting. I haven't had any problems as long as some discretion exercised. I can usually keep the hole neat and close to the exterior of the box. Close enough not to worry about anything but fines and cream coming out the gap. Very few issues if the cores are being filled with concrete.
Don't forget to install a ground screw into the metal box before the grout is poured.
~Peter
Good point. Frequently forget about it and have to do a little work with a scribe and a pair of Kleins, the electricians hammer, to free up the hole. Good thing green concrete is soft.
Thanks for the help. I am a newby to the forum. What is the proper ettiquete ... should I respond and thank everyone who responded? How do I terminate the question once I have gotten a good answer?
IMO, a separate message to each respondant is unnecessary, but several people do that. A single message thanking people individually is a gracious thing to do. I've never noticed anyone getting his feelings hurt by a thanks to all message.
No need to close out the thread. You may yet get responses from people who don't log in as often. Other people may think about it for a while and then decide they have something to add. Eventually it'll die a natural death.
No Emily Post or whoever on Breaktime. Usually an "attaboy" is appreciated, however, on a very slow connection, it is sometimes less than thrilling to wait several minute to see the post that simply says "thanks"...
Breaktime threads are not terminated - unless the Breaktime police decide that you have far exceeded normal decorum, which is very rare. Often, threads take on a life of their own, so it is better to not feel that you "own" a thread that you started.
The proper response is to write your thanks on a $50 bill and mail it to each contributor, at least the good ones. Everyone else get $20.
A simple 'Thanks all' would do. You can address any of those who were particularly helpful or annoying by name with the the appropriate praise or abuse. Have fun.
Telling us how everything worked out is an amenity that is appreciated. Often people post problems, many times multiple solutions are offered but we never get to hear which solution worked and how, or if, the problem was solved.
Are you running conduit out of the box? If so use a steel masonary box w/ the face covered in duct tape,and a ground tail in it.Mortar it in place as you lay up the block.Grout your cells later and the box will never move. Or is this an after the fact deal?