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  • #16
    Re: surface mounting in block walls

    Those catalogs were very helpful.
    Thanks Woussko.
    Now we have 4x4 boxes (leaning towards the 2 and 1/8 deep).
    1/2 emt; most we will have is 6 number 12's in one conduit.
    This is a small addition; 2br 1 bath and a laundry; we are thinking of putting in a sub panel as the home runs will go 45 feet without it.
    4-20A circuits; 1 for the wet areas; 2 for the br's and 1 for exterior and future.
    Was wondering why ceiling boxes are octagonal.
    Also what is the O.D of 1/2 emt.
    Can you run 1/2 emt down the wall surface and into the top of the box without an offset coupling.
    Chenchen.

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    • #17
      Re: surface mounting in block walls

      They call it 1/2" EMTube but the inside diameter is not 1/2". My old 1999 NEC book has an internal diameter of 0.622". Don't know what the outside diameter is.
      Use THHN type wire like Woussko said it is thinner and has a hard covering for pulling in conduit. You also need to pull a ground.

      If you can find a 1/2" bender it is easy to use to offset the EMT. Usually somebody has one lying around. The offset fittings are very costly at least where I live.

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      • #18
        Re: surface mounting in block walls

        Unless it is a local code, he doesn't need to pull a ground if he is using solid runs of EMT. EMT is rated for grounding as long as you use the correct fittings, which is pretty much any commonly used fitting, pulling another ground would be redundant.

        Also, you can just go from the wall into a fitting, but it will not look good or professional. Any local rental store or hardware store should have a 1/2 EMT bender for rent for cheap. Doing a 1/2" box offset is pretty simple.

        The outside diameter of 1/2" EMT would be fairly close to 3/4" or 13/16".

        The only reason I have ever come up for ceiling boxes being octogonal is because the mounting straps on most fixtures are too short to stretch across a 4x4 diagonally. An octogon has a shorter distance between the screw holes.

        If you go over 6 conductors (not counting a ground) in a single conduit you have to derate your conductors to 70% of the 20 amps or 50% if you go over 10 in a single conduit. So keep your runs to 6, and you will only have to derate to the standard 80% which is what you have to do anyways.

        Jeff

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        • #19
          Re: surface mounting in block walls

          Didn't know that, in Ontario we need a ground in EMT runs.

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          • #20
            Re: surface mounting in block walls

            1/2 inch emt only in traffic areas; romex through the roof trusses to a JB then down the wall in emt at each of the boxes.
            Chenchen.

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            • #21
              Re: surface mounting in block walls

              I always recommend using 1900 (4X4") boxes for exposed work.
              Knock out the center knockout in the back of the box, drill a 1/4" hole in the wall and use a plastic anchor, fender washer and #10 sheetmetal screw to secure the box to the wall. This will allow you to plumb the box for a neat appearance. It is pretty difficult to drill holes right where you want them as the carbide drill usually kicks off your mark due to the irregular concrete surface.

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