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Thread: Electric Boxes and Mud Rings

  1. #1
    Join Date
    Jul 2009
    Location
    Sandwich, MA
    Posts
    98

    Electric Boxes and Mud Rings

    I'm a bit confused about mud or plaster rings for electrical boxes and know some of you guys can provide the needed guidance.

    I will be using 4 x 4" metal boxes to each hold a single 240 volt receptacle in my workshop. The workshop is wood-framed 2 x 4" construction. The walls will be insulated with fiberglass batt, then covered with 3/16" thick plywood sheets as paneling. The paneling will be screwed to the studs so that it is relatively easy to remove in case I want to modify the wiring in the future.

    There appears to be two types of metal covers for the metal electrical boxes. Type One has a flat perimeter, which touches the edges of the box, and the inner portion of the cover is raised either 1/2" or 5/8" depending on the cover design. Type Two is entirely raised, typically 1/2", even along the outer perimeter where it is sitting on the outer edges of the box.

    My understanding, which may well be completely wrong, is that Type One is called a mud ring or plaster ring that is installed on top of the box prior to drywall being installed. The drywall will cover the flat perimeter portion of the mud ring. The raised portion of the mud ring will sit in a hole cut into the drywall so that this portion of the mud ring is flush with the outer surface of the drywall.

    My understanding is that Type Two is used for exposed wiring (no dry wall or surface covering of any type) and I suspect this type of cover should also be used with a handy box which has rounded corners so that it won't "catch stuff" like an exposed square-cornered metal box can.

    I'd appreciate if some of you experts would tell me where my understandings stated above are wrong.

    Here's where I'm really confused. If I'm using a single 240 volt receptacle in the box, the box cover will have a single small hole in the center of the cover for the front face only of the receptacle to protrude through. This means that the receptacle would need to be installed into the mud ring from the back side and the mud ring installed on the box prior to the dry wall being installed. If this is true, then the receptacle could not be replaced if it failed or if a different type of receptacle was needed in the future without cutting away the drywall from the perimeter of the raised portion of the mud ring. While I'm planning on using wood paneling instead of drywall, the same problem applies since I would prefer not having to cut the paneling to replace the receptacle or to unscrew and remove the entire panel to replace the receptacle.

    Is the solution to install a mud ring with a full single-gang opening instead of a mud ring with a single small hole for just the front face of the receptacle to protrude through? Then install the paneling to cover the non-raised portion of the mud ring? Then install the receptacle into the full-single gang opening in the mud ring? Then install a single-gang cover plate on top of the mud ring and paneling? This single-gang cover plate would have the small hole in the center for the protruding front face of the receptacle. This would allow the receptacle to be replaced in the future without cutting the paneling by removing the single-gang cover plate, then removing the receptacle. If so, I assume that the box should be installed sufficiently deep within the wall cavity so that the back of the single-gang cover plate is flush with the outer surface of the paneling. Am I completely off base here? If I am, what solutions do you guys propose?

    Thanks

    Bob DeRoeck

  2. #2
    If you can't get the receptacle out without ripping the drywall up you are using the wrong sort of cover. It doesn't meet the code level for accessibility.
    A mud ring doesn't cover up where the device goes, it essentially just narrows the opening from a double box to that you would get from a single box.
    Further, the mud ring opening (or the box if you're not using one) must be within a quarter inch of the finished surface.

  3. #3
    Join Date
    Dec 2006
    Location
    SF Bay Area
    Posts
    36
    Speaking not as an electrician, but as a homeowner who's done a bit of work replacing receptacles and boxes in my house.

    Mud rings fit on 4" square boxes, providing a greater box volume for receptacle/switch installations. They are installed, sheetrock is placed, and the rock is cut for the smaller opening provided by the mudring (either 1 or 2 gang). Any (most?) receptacles/switches can be mounted in the mud ring. Switch or receptacle cover plates are then mounted to the receptacle/switches.

    The 2nd type of cover you describe is used for exposed installations. The switch/receptacles are mounted to the inside face of the cover, which is then attached to the exposed box. Access to the switch or receptacle comes by unscrewing the cover.

    Here is a link to a catalog which has some of the Leviton cover plates for 1/2 gang boxes/mudrings.

    Here's where I'm really confused. If I'm using a single 240 volt receptacle in the box, the box cover will have a single small hole in the center of the cover for the front face only of the receptacle to protrude through.
    Only if you're installing exposed boxes. These box covers are not used for in-wall installations.

    This means that the receptacle would need to be installed into the mud ring from the back side and the mud ring installed on the box prior to the dry wall being installed. If this is true, then the receptacle could not be replaced if it failed or if a different type of receptacle was needed in the future without cutting away the drywall from the perimeter of the raised portion of the mud ring.
    As answered by Ron in the previous comment.

    Is the solution to install a mud ring with a full single-gang opening instead of a mud ring with a single small hole for just the front face of the receptacle to protrude through? Then install the paneling to cover the non-raised portion of the mud ring? Then install the receptacle into the full-single gang opening in the mud ring? Then install a single-gang cover plate on top of the mud ring and paneling? This single-gang cover plate would have the small hole in the center for the protruding front face of the receptacle. This would allow the receptacle to be replaced in the future without cutting the paneling by removing the single-gang cover plate, then removing the receptacle. If so, I assume that the box should be installed sufficiently deep within the wall cavity so that the back of the single-gang cover plate is flush with the outer surface of the paneling.
    Again, I'm not an electrician, just a homeowner elaborating on my understanding of these installations based on my experience. Were this my shop, I'd probably go about it as you described above. As Ron said, set the box depth so that the edge of the mud ring is flush with (or slightly inset from) the exposed side of the plywood.

  4. #4
    Join Date
    Jul 2009
    Location
    Sandwich, MA
    Posts
    98
    Thanks, Murray.

    You has cleared up my confusion.

    Bob

  5. #5
    I know this wasn't part of your original question, but I would be reluctant to put 3/16 paneling over bare studs. Too flimsy!

    It wouldn't cost you very much extra to go 1/2 inch. This will also line up your jambs for windows, doors, and even the mud rings.
    Last edited by David Larsen; 04-23-2011 at 1:10 PM.

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