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Thread: In floor electric

  1. #1
    Join Date
    Aug 2007
    Location
    Lancaster PA
    Posts
    24

    In floor electric

    I'm going to be pouring the slab in a month in the 40*60 man cave. About half will be woodshop. I'm still not quiet set on floor plan, but an close. Going to run sch40 pvc conduit under slab. Thought on boxes or general things to consider? Most all equipment out in the center is 220 single or 3 phase, less than 10 hp. Thanks!

  2. #2
    Join Date
    Jan 2014
    Location
    Panama City, Fl
    Posts
    9
    Assuming that an electrical panel is in visual range (NEC disconnect req), I prefer to use PVC boxes and hard wire everything with metal flex or heavy rubber cable. Use big floor boxes and the biggest conduit that will fit (probably 3/4"). Just don't like the idea of upward facing plug/receptacles and sawdust. Be generous, the cost of the boxes and PVC is trivial compared to the total project.

    I actually ran an air line over to my work bench in one of my spare under slab electrical raceways (didn't think of that in the original layout) and have small pneumatic tubing to operate air cylinders (DC blast gates) in with several of the electrical runs.

  3. #3
    Join Date
    Aug 2007
    Location
    Lancaster PA
    Posts
    24
    So to be clear, stub up 3/4. Once poured, cut off flush. Attach a plastic box and they cable/or flex metal conduit? Good idea about the airlines!

  4. #4
    What about making raceways in the concrete and putting metal grates over them. Now you still have access to the electrical to upgrade.

  5. #5
    Join Date
    Jan 2014
    Location
    Panama City, Fl
    Posts
    9
    The floor boxes that I used are round PVC and designed to be installed with the upper lip flush with the finished pour/ floor. There are 4 bosses for PVC conduit near the bottom and probably 6" deep. Might have to go to a real electrical supply house to get some with just a flat blanking plate cover (most standard trim/covers are for a receptacle).

    When you get ready to connect the machines just knock some holes in the cover. If you are directly under the machine just flex/ cable straight up, if you are running over a short distance then use a right angle flex connector and run the flex over along the floor. Getting right under the machine makes for a neat installation but can be a PITA depending on the exact configuration and what is going on with dust collection (mine is all in the floor). Sometimes setting over to one side away from foot traffic can be a little easier. You can daisy chain a couple of boxes back to the electrical panel (or you can make each a single home run). I also ran a couple of PVC stub ups from the last box over and up into a wall box. This gives you the option of getting a circuit over to that wall in the future or in my case an airline feeding backwards to the work bench. I did mine over 30 years ago and it has worked out pretty well but know what they say about hindsight.

    The trench duct would be the ideal in future flexibility but then you are into a Cadillac when maybe a Ford will do.

  6. #6
    On the jobs I worked on, when we ran PVC conduit under the slab we had to stub up with GRC. The GRC was sturdy enough to handle having a box mounted to it and stand on its own. We were sometimes required to secure it by other means so we used unistrut mounted to L brackets fastened with drop-in anchors into the slab if we couldn't secure it to a column or wall.

    I know you're only doing a shop but this might give you some ideas.

    Only the GRC will be exposed after the pour.


    Ready for concrete.


    After the pour.


    Boxes mounted to GRC coming out of the slab.

    During construction, some boxes get banged up and have to be replaced. Others can be bent back into shape. I like the metal boxes because they can take a beating and you can bond a ground to it. Any metallic conduit coming from that box is case grounded so you don't need to pull a ground wire.

    I realize a lot of this is overkill for your shop but it may help you design your layout.
    “Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  7. #7
    If you put in boxes flush to the floor, you can put in twice as many as you think you need. Then cover the ones you don't use and you can still walk over them. It allows you to not be married to your current floor plan and rearrange equipment in the future as you see fit. Also, over engineer - 30 amp as opposed to 20, and don't forget 110 as well as 220.

  8. #8
    Join Date
    May 2014
    Location
    Alberta
    Posts
    2,162
    When I built my shop I ran pvc conduit to two locations under my slab. One is the area where my tablesaws are in the center of my floor more or less. And the other was where I set up my jointer and planer side by side. After I poured my floor my electrician showed me RV pedestals,about 24''high and steel with a box that can house four receptacles. We used two receptacles on each pedestal for machines (220) and the others are extra 110v. the extra 110 are really nice in the center of the floor. Mike.

  9. #9
    Another option is to pour a trough across the floor and run the electrical, air, dust collection and even water as you needed it. A lip so whatever you use for covers leaves the floor flush. If there are no vehicles driving over it thick plywood will suffice and 1/4" or 3/8" steel checker plate will take forklifts and cars. My shop is 24'x 28', above my garage and I'm already wishing I'd run 110/220 receptacles to the centre.

    Pete

  10. #10
    If you're 100% certain nothing is ever going to be moved, run the conduit in the concrete. If you're less than 100% certain, just run it overhead and do cord drops.

    Anyone who's ever taken apart a dust collection system will tell you running it where you can't access it is planning for anger management classes. Sometimes stuff gets sucked up, and creates blockage. Pretty simple when it's a couple of connectors to pull a stick out.

  11. #11
    Agree with Martin Wasner. Have my machines powered with drops from ceiling, and have reconfigured my dc twice. You can always come up with a better arrangement for your machines after you have used them for a while. And then, you get a new machine and everything is screwed up.

  12. #12
    If you are pouring concrete, I would suggest in floor tracks. See photos of what I did. Large enough for dust collection, air, and electrical. I've been very happy with this approach. Setup so can be easily re-configured as needed with removable plates. Ran two tracks across entire width of woodshop. IMG_20170126_195147.jpgIMG_20170126_195209.jpg

  13. #13
    Nicely done David. That was what I was trying to get across earlier.

  14. #14
    Join Date
    Jul 2008
    Location
    Courtenay BC Canada
    Posts
    2,750
    David .. how deep are those troughs ? Is the slab over 4" thick ? are the holes lined ? or is there gravel at the bottom ?

    Thanks

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