Electrical box for exterior flood light

Discussion in 'Electrical and Wiring' started by kdrymer, Jul 10, 2019.

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  1. Jul 10, 2019 #1

    kdrymer

    kdrymer

    kdrymer

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    I bought this exterior weatherproof round electrical box to surface mount to the exterior wall on my garage for a flood light, in which I will have NM Romex 14/2 cable entering through the back of the box. I haven't been able to find a NM style cable clamp connector that will work with this box, because the knock out holes are threaded. Is there something else I can use to secure the cable, or should I be looking for a different kind of box?

    https://www.lowes.com/pd/Hubbell-Ta...ard-Round-Ceiling-Wall-Electrical-Box/4005487
     
  2. Jul 10, 2019 #2

    hornetd

    hornetd

    hornetd

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    Those hubs are 1/2" pipe threads just like the ones on 1/2" rigid metal conduit. The threads of a "3/8ths" NM connector are the same.
    [​IMG]
    Just remove the lock nut from an NM connector and thread it into that back hole of the box. You will need to drill a large enough hole into the wall to fit the screws and ears of the NM connector behind the box OR you will have to slide the box over the cable, tighten the NM connector onto the cable with the threads facing the inside of the box, and turn the box to thread the connector into the inside of the box. Remember that type NM cable is not laboratory listed for use in wet locations so you will have to calk the threaded hub around the cable and the edge of the box very carefully to exclude any water from in or behind the box. Do not calk the bottom edge so that any water that does make it past the calking on the top and side edges can readily drain away and not accumulate.

    Another way to do this, if the cable is not to be fished into a wall to reach the back of the box, is to thread a rigid conduit nipple
    [​IMG]
    into the box wrench tight after applying Teflon pipe tape or pipe thread sealant (Pipe Dope) to the threads. Do not apply wrenches or pliers to the threads of the nipple. In the case of the close nipple shown above you tighten it by tightening the two adjacent threaded fitting and box hub. That nipple will go through any cleanly drilled 7/8" hole. As long as the hole was drilled at a right angle to the mounting surface the back of the box will fit tightly on that surface. Clapboard, ship lap, and similar sidings will not have a surface which is plumb so if your siding is similarly irregular then do not drill a "Level" whole but rather one that is at right angle to the mounting surface so that the back of the box will sit flat on that surface. Since you will have waterproofed the Rigid Conduit Nipple threads there will be no need to calk the edges of the box. The nipple used should be just long enough to have threads protruding on the inside of the mounting surface. The nipple will need to be longer if the inside wall is sheathed with finish materials of some sort. Screw a threaded rigid conduit connector
    [​IMG]
    to the inside end of the rigid conduit nipple. The end of the connector only needs to be inside the stud cavity in an unfinished wall. In a finished wall with unconcealed, surface run, NM cable the rigid conduit coupling will need to be flush with the wall surface or no more than 1/8th" recessed into the surface over which the NM cable will run. In an unfinished wall screw a straight NM connector into the coupling and then install your cable into the connector and tighten. If the wall is finished, and you are using surface wiring, thread a right angle NM connector into the coupling so that it will sit tight to the wall. In either case use an insulated bushing on the threads that protrude into the inside of the box.


    In either case all of the hub blanks must also be waterproofed with Teflon tape or pipe dope. Do not fasten the box to the outside wall until you have the NM clamps screwed into the boxes threaded hub or you have correctly positioned the right angle NM connector for the direction the surface mounted cable will come from.

    If the cable is to be fished to the box's location use the technique in the first paragraph after fishing the cable out of the hole in the outside wall.

    Good Luck!

    --
    Tom Horne
    Retired Electrician.
     
  3. Jul 10, 2019 #3

    bud16415

    bud16415

    bud16415

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    A regular conduit clamp fitting or any type of conduit connector will screw right in those pipe threaded holes. just remove the ring nut.


    https://www.lowes.com/pd/Sigma-Elec...ce-Entrance-Connector-Conduit-Fitting/1087221
     
  4. Jul 11, 2019 #4

    kdrymer

    kdrymer

    kdrymer

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    Thank you both for the help!
     
    bud16415 likes this.

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