Wiring In Concrete Ceiling & Covering Junction Box

Discussion in 'Electrical Forum discussion & Blog' started by christo, Jun 6, 2009.

  1. christo

    christo New Member

    Messages:
    22
    Hello
    Several questions kindly.
    I have a 10" concrete ceiling and I want to route the feed from an existing junction box to a point that is centered in my dining room to hang my fixture.
    My plan is to notch out a channel approximately 2 feet from the box to my center point. Any special wire needed.

    Also the depth of the box is 4" that needs to be filled in so that I may blend it in with my ceiling covered by joint compound. Perhaps foam for 3" then finish with joint compound feathered in to match the ceiling grade then painted. The whole point is to eliminate the swag of the chain/wire dreaded look. Why electricians put boxes way off center, I never understood.

    Any advise would be greatly appreciated.
  2. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    If this is a actual pre or post stressed beam concrete ceiling then you can not cut any kind of notches into it.

    As for wire, as I understand it you can't just run wire in concrete, it has to be inside of some sort of conduit.
  3. christo

    christo New Member

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    22
    The concrete was poured in place. The notch should not be any bigger than 1 inch tops 1.5
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,047
    Location:
    Cave Creek, Arizona
    ceiling

    IF that is a 10" SOLID concrete ceiling the obvious question is how big was the plane they intended to land on it, or were they planning on using it as a driveway for semi trucks? We cannot answer the question because we do not know if there are tension cables or reinforcing metal in that lower 1 1/2" of the ceiling/floor. The physics of stress would make the bottom of the slab the most likely point for any reinforcement because that area is under stress while the upper portion is under compression. I cannot imagine any "patch" that will make a 4" deep box look "invisible".
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    My personal thought is that it is a VERY bad idea to cut a notch in that. You should probably check with a structural engineer first for a blessing or the correct way to do it, if allowed at all. If I had to guess, this is a flat in a high-rise. There's a lot of liability involved here...you don't want to be responsible by doing it wrong or compromising the structure.
  6. christo

    christo New Member

    Messages:
    22
    I should have mentioned I have already done two sections by notching out about a 3/4" channel the length of about 4' to run track lighting without any problems. I did not have to deal with a junction box however. I'm not an engineer but I hardly think that this would undermine the concrete. It is only 3/4 of an inch. I did not have any issues with metal or rebar.
    I live in a condominium, hence the poured concrete. Gentlemen, I DO UNDERSTAND ALL OF MY CONSEQUENCES.

    My problem is this 4" junction box to conceal. I guessed the slab was 10"
    Maybe it is 8" I do know that the junction box is 4"

    This run I am trying to accomplish would be only 2' Again does anyone think I could use foam for maybe 2" or so, then use a high strengh quick crete then then finish it with joint compound feathered in to match the ceiling grade then paint it.

    If someone has another way, I would very much appreciate any help.
    Last edited: Jun 7, 2009
  7. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    I wouldn't chop out any concrete, ESPECIALLY for a Jbox.

    I'd do it right and furr the ceiling down if I wanted concealed wiring.
  8. christo

    christo New Member

    Messages:
    22
    Thanks for replying 220/221

    Could you please explain a little further, as I am not at all clear on what you said.

    Thank you.
  9. ask condo administrators for their understanding of what part of the slab (which is your ceiling, and is the neighbor's floor) you can safely take out. Every person posting above has said it the same way: this is important, very important. The entire building might collapse if it is weakened in specific ways. Unbelievable in your mind? Consult a couple others. Everyone who has posted above has said the same thing. It's now time for you to talk to others in the building.
  10. Cookie

    Cookie .

    Messages:
    5,658
    Location:
    .
    I know someone who uses fake decorative timbers which spanned their ceilings and from that timber you could maybe put a junction box instead of the concrete ceiling. Just a suggestion. To me that might be better than to maybe compromise the structure of the ceiling.


    http://www.fauxwoodbeams.com/about_portfolio.php
    Last edited: Jun 8, 2009
  11. christo

    christo New Member

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    22
    Thanks for responding Cookie

    Good idea on various applications, however that would not fit my decor.
  12. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    Install metal hat channel on the concrete ceiling and drywall over that. That gives room for cable/conduit between the ceiling and the drywall.

    It's not an inexpensive task but it is the proper way to do it.
  13. christo

    christo New Member

    Messages:
    22
    Hello 20/21

    Thanks for the idea, however that would be out of my budget and would force me to scrap the project which I really don't want to do.
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    And repairing the ceiling if it cracks your upstairs neighbor's floor is in the budget? There are right and wrong ways to do things, and I think if you asked a structural engineer, he would blanch at what you are trying to do.
  15. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    Notching the cement creates a stress relief point
    Any stress (existing or new) can then cause the concrete to fracture
    Once it does they will then find out why it fractured
    Then you will be on the hook to pay for full repairs

    Hopefully it will only fracture & not be a catostrophic failure

    To meet code it has to be in conduit
    Now you are talking an even deeper notch
  16. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    Move your table ? :cool:
  17. christo

    christo New Member

    Messages:
    22
    The consensus of opinion seems to say my project is a no no. Not sure what I will do. Maybe consult a structural engineer. Thanks, however for all those taking the time.
  18. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    Unless you know one personally it would be cheaper to create a drop ceiling for the lowest j-box you could find. Drywall, some lumber or metal channels, nails, cornerbead and paint. Less than $100 if it's a relatively small area. This project could be accomplished nicely in a day or two at the most.
  19. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,386
    Location:
    Yakima WA
    You said in one of your posts that you understood all of the consequences. I've got to say that you don't understand the consequences or you would not be asking the question. First, condos usually mandate that licensed and bonded contractors be used for plumbing and electrical work and that the condo association approve the work before it is done. The contractor is required to pull permits for the job and that means it will have to be inspected. I know that's a lot of bother that you'd like to avoid, but you legally can't. As it has been pointed out, your idea will weaken the structure which will put you on the spot for any and all problems that arise. If and when the condo association finds out what you have done, you will meet with more attorneys than you thought existed. It doesn't matter that doing the job right will cost more money than you want to spend. You either do it right or you don't do it. You are in dangerous water, best heed the warnings.:eek:
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