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Thread: Power outlets in concrete floor

  1. #1
    Join Date
    Oct 2008
    Midlands of South Carolina

    Power outlets in concrete floor

    I have a pole building scheduled to go up in Aug (temp living quarters and shop). The concrete floor will be 40 x 70 ft. I am thinking it might be a good idea to have power outlets running down the center of the floor.
    Is there a standard spacing for this?
    Would it be better to drop power from the ceiling? (14 ft)
    Would the outlets make it difficult to level the concrete?

    Pros and Cons?

  2. #2
    Probably easier to drop from above,
    What about washing the floor, etc?...
    Are they going to be flush mounted? etc...
    It might be more difficult for the concrete guys to screet/level it with the boxes in the floor, plus you have to run the conduit for all the boxes, thru the floor before the concrete pour, etc.....
    Dave W. -
    Restoring an 1890 Victorian
    Cuba, NY

  3. #3
    Join Date
    Dec 2006
    Toronto Ontario
    Rick, commercial buildings use floor boxes frequently.

    They have a sliding interior that allows the box to be adjusted for height.

    If I was building a dedicated shop I'd put the dust collection and power in the slab.

    Regards, Rod.

  4. #4
    Flush floor boxes in the slab would be a very easy install, there are a number of manfacturers who make either rectangular or round PVC boxes that can be fed with Schedule 40 PVC. The NEC now specifies that the covers be gasketed to be able to handle the type of water that a mop down might involve. Since they're PVC, the boxes can be sawn flush after the pour, and adjusting rings allow for final leveling of the covers. Google a Carlon E971FB for an idea of what I'm talking about.

  5. #5

    You can use those protection boxes plumbers use for toilet rough ins. Basically, it shields yr terminal points with a 1ft square dead space so you can adjust the final position of yr receptacle after poured.

    You might consider pouring the concrete floor, and then adding sleepers and plywood or OSB atop that. The airspace under there will be a great place for running electrical. I also think the wood floor will be more comfortable to work on.

    Even if you don't want yr dc running underground, it'd be very cheap to do the 'rough' plumbing for that now...

  6. #6
    Join Date
    Oct 2007
    Post Falls, Idaho

    Code issues

    Be sure and check all of your local codes. I wanted to do the same thing on my pole building but was told that since I had a large enough door to permit vehicles, RVs, etc., that all outlets had to be a minimum of 48 inches (I think) above the floor and floor outlets were not permitted no matter what type they were. The inspector who did the final sign-off talked about propane and other fumes settling to the floor and causing significant hazards around electric sparks, yada, yada. He said if I had just man doors and not the large door I could run as many as I wanted. Just something to check on before spending the big bucks.

  7. #7
    Join Date
    Oct 2008
    Midlands of South Carolina
    I will check on the codes - had not considered that possibility.

    As far as DC ducts in concrete - I don't have a layout yet of tools and such - will depend on what I do with the temp living quarters. Not sure where I would run them.

    Will start with concrete floor - may add wood later (possible radiant heat)

  8. #8
    Join Date
    Nov 2006
    Fallbrook, California
    I have a 220 outlet and a 110 outlet in my floor for my table saw and its DC. Both are flush mounts. Surprisingly, considering all the other hassles I had with the Building and Safety people, there were no problems with code. My electrician knew just how to design and install them to code. I've already found it very handy having my table saw in the center of the shop and no cords to trip over. If I could start over I would have floor outlets installed where I plan to put my workbench. Since my workbench is very close to an outlet I'll use one of these:

    It's not a great solution, but it will work.
    Don Bullock
    Woebgon Bassets
    AKC Championss

    The man who makes no mistakes does not usually make anything.
    -- Edward John Phelps

  9. #9
    Join Date
    Oct 2006
    Mid Michigan
    You can put the power in the concrete if allowed by code in your area but prior to committing to them make sure you get a price, some of the boxes can be very expensive.
    David B

  10. #10
    Join Date
    Dec 2003
    West of Ft. Worth, TX
    The other possibility would be to build a trough down the middle of the shop. Have a ledge built on either side 1 1/2" below the finished surface, then you could run what ever you want down that, and wire to a box that is flush mounted, or on a stalk, in a piece of say 2 X 12 that fits the trough. Easy to change, easy to add to, easy to roll mobile equipment over. Don't know about code though. You'd still need to check on that. Jim.
    Coolmeadow Setters...Exclusively Irish! When Irish Eyes are smiling....They're usually up to something!!
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    No, I'm not an electrician. Any information I share is purely what I would do myself. If in doubt, hire an electrician!
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  11. #11
    Join Date
    Jul 2008
    Tomball, TX (30 miles NNW Houston)
    I put conduit in the floor of my shop for the TS, compressor and the water well/treatment equipment.

    Wish I had put DC in the floor for the TS. I'm happy with it.

    It does make the finishing of the conrete a little more difficult but ever house on a slab has pipes sticking up.

    Finishing is an 'Art & a Science'. Actually, it is a process. You must understand the properties and tendencies of the finish you are using. You must know the proper steps and techniques, then you must execute them properly.

  12. #12
    Quote Originally Posted by J. Scott Holmes View Post
    I put conduit in the floor of my shop for the TS, compressor and the water well/treatment equipment.

    Wish I had put DC in the floor for the TS. I'm happy with it.

    It does make the finishing of the concrete a little more difficult but every house on a slab has pipes sticking up.

    The worst thing one do is use PVC for the stub up, 1) it needs support & cannot be used where "subject to physical damage" (Sch 40) , 2) PVC is likely to shatter so use rigid steel conduit for the portion coming up through the slab. With PVC a equipment grounding conductor is required anyway & metal boxes need to be bonded to it, so the mixing of metallic & non-metallic conduits is a non issue.

  13. #13
    I placed four pvc boxes in my slab and stubbed it all out with 1" pvc conduit with no problems.

  14. #14
    Join Date
    Sep 2008
    Raleigh, NC
    Personally, as a former electrician, I wouldn't do this, particularly flush-mount recepticles. In a woodshop, wood dust is going to get into things, no matter how good of a dust collection system you put in. The problem with flush-mount recepticles is that every time the floor's swept, unless you're really cautious, you're likely to get wood dust in the outlet. Eventually, that can cause tight plugs, or perhaps even non-functioning outlets because the wood dust charcoals on the contacts and insulates them. It takes a while for this to happen, but I've seen (and repaired) such problems.

    There are several other issues - accidentally rolling a mobile machine over one and damaging it, spilled liquids causing a short, and the irritation (and expense) if a fault develops between the distribution box and the outlet, which requires a conduit pull to replace the wiring.

    Finally, you've also the consideration that they're not movable. It's pretty rare for a WW to not decide to rearrange the shop at some point to accomodate another machine or another bench, etc...

    The same issue arrises with stub-boxes placed 12" above the floor, with the added fun of having something ideally placed to give you a trip or whack in the shin when you're carrying a large, awkward and heavy board.

    My choice would be overhead cord reels. They're easy to relocate, they're out of the way when not in use, and easy to repair/replace.

  15. #15
    My DC and elec. is under concrete. Very handy I might add.

    I did not put in the flush boxes. I ran the conduit up above the concrete, an inch or so. Then I mounted the boxes on the conduit.

    Good planning and layout is the key here.
    Like for a table saw, plan the electric outlet so it will be under your outfeed table.

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