Electrical Box in 2x6 T&G ceiling

Discussion in 'Electrical Forum discussion & Blog' started by Count Fred, Mar 12, 2008.

  1. Count Fred

    Count Fred New Member

    Messages:
    3
    I have a 2x6 car decking ceiling with a 2x4 cavity above through which to run electrical and plumbing. I'm puzzled by the best type of box to use to mount light fixtures in the room below. Obviously I'm going to want to cut into the ceiling to get the box flush with the bottom surface of the T&G, but I will then need to fasten the box somewhere in the ceiling. Most boxes only want to account for 1/2 wallboard, and I effectively have 1.5" of material to deal with.

    Is my best bet going to be a ceiling fan type box, with a 2x4 between the cavity joists?

    Thoughts,
    JFS III
  2. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,734
    Location:
    Central Florida
    Most light fixtures expect a 4" "ceiling box" which is a kind of rounded-off square box (also called an "octagon box"):

    ceiling box.jpg

    I always mount them as you described -- on a 2x4 in the joist cavity. A similar box is available for about 3x the price called a "ceiling/chandelier box" and comes with hardware for mounting fixtures like fans or (!) chandeliers, but the weight of your fixtures will determine which you need.

    Get the kind of box that has knockouts in the bottom (shown), since you won't be able to bring the cables in to the side of the box. Drill or saw a hole in the 2x4 to match up with the bushing in the box and pass the cable through the hole.

    They make these boxes with a mounting tab attached, which would eliminate the requirement for the 2x4 (just mount it to the side of a joist), but I don't like them -- you're limited in where you can mount the box, and I wouldn't trust them with any weight:

    octagon box.jpg

    Do you have access to the space above the ceiling?
    Last edited: Mar 13, 2008
  3. frenchie

    frenchie Jack of all trades

    They also make them with a hanger bars, like in this pic. The steel version (couldn't find a pic) will have 5 K/O's on the bottom, use the center one to attach to the hanger bar, leaves you 4 you can use.

    (edit: "can't find a pic" - doh! - the top picture in Mikey's post is the kind of box I mean)

    Attached Files:

    Last edited: Mar 13, 2008
  4. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    Why not use a remodel box and screw through the edge of the box in to the 2x6. I know screws through side of box may not be code compliant, but it would work. Other option could be a remodel box with longer screws for the tabs, or possibly with a box extension if they make an octogon extension.

    Jason
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,262
    Location:
    New England
    I think you can use screws to attach the box, but can't have screws running through the box with exposed threads that could cut the insulation.
  6. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    Thats why they make these...
    http://www.contractor-books.com/SmartBox.htm
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