ECN Forum Forums General Topics of the Trade General Discussion Area Running Conduit in Slab

Solar -
Yes I mean rigid metal conduit ( rmc )
we screw a pvc female adaptor to the rmc 90.
As far as bonding the rigid metal conduit...
the bond is created when we install locknuts at the box then we pull a grounding conductor through the conduit then bond the box with a approved green ground screw. We pull grounding conductors in every conduit. Oh by the way I use schedule 40 pvc in slabs

Be Smart and Do It Right

[This message has been edited by luckyshadow (edited 02-04-2005).]

Lucky,

Thanks for your reply.

When Im running underground conduit, I like to use pvc, and then for the stub ups, cut a 10' stick of RMC in half, and bend stub 90's on the threaded ends. then you can change over with an F/A underground, and have a full 4 feet of RMC comming out of the slab, which I like to paint orange for safety (if its not going to be exposed). There is nothing worse that a guy drive over a 90'that has a short nipple with a lift and snapping the threads off. And with the extra length, if your going into an outlet inside a wall, you have no problem hickeying it over to exactly where you need it and cutting it to length. If you have many stubs that are gonna be going into a panel, then go ahead and strap them to strut, with the back of the strut where the face of the wall will eventualy be (if the panel will be mounted strait to the wall), and support the strut by using 1/2" or 3/4" emt on each side of the rack. With the 4' or so of RMC coming out of the slab, you dont have to waist time and money with changing over to emt or cutting custume RMC nipples, you just have to sawsall all the pipes down to the correct length, and use ridgid set screw connectors. and you can just break the emt stakes off at the level of the slab, once it it cured.

When running conduit and boxes in concrete walls, I like to really support the conduit to the rebar with tie wire every 5 feet or even closer, and make sure the boxes are REALLY WELL supported, because when it comes time for the pour, that concrete is gonna be dropping onto your work from up to 10 feet above, and you dont want anything dislodged. One more thing I learned when installing boxes in concrete walls, if the boxes your installing are on the open form side, that is, the side that the form is not in place yet, so workers have room to work. Try to make sure there arent 20 iron workers climbing around on the rebar, because they may be pulling the entire mat out, while they are on it, and your measurment for the face of your box will be off. You may end up with the face of the box up to even an inch deep inside the concrete (have fun finding it with a hammer). Which brings me to this point. Make exact as-builts for all your boxes, so you know where to look if this does happen. (nobody's perfect, and you might end up needing to search for a box or two.)

Now a question for the guys that are familiare with work in slab walls. I've never had a problem with using regulare metel 4sq boxes with mud rings, and just taping them up really good with duct tape, the inspectors never had a problem with it either. But are there specialty boxes for this purpose? And do you use them, or do you just go with the regular boxes? I'm guessing 300.6 b permits it.

davey

I use either a standard 4" square with mud ring or a standard masonary box - either way Duct Tape becomes your best friend ! You can't use too much in this application. Another trick I have been using and teaching my apprentices is ... when roughing in boxes in concrete forms I have them "pack " the boxes with as much paper , plastic as will fit. this way should concrete find a way in - the box is already filled up. I do this also when installing floor boxes in slabs. ( which I forgot to mention to RobbieD - sorry ) Makes for a surprise if the person opening up the box later on doesn't know about it, you should hear some of the comments.

We use 4^2s with mud rings duct taped here on the few times we have done it inside the walls. We usually don't bother trying to run inside walls, seems like half our boxes end up unusable after the concrete workers get through with it (And yes we oversecure everything).

Make sure to put a pull string in your underground before they pull. Its alot easy to fix an issue now than later. And later you know who to blaim if your pull string doesnt work after they pour.