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Thread: Silly Question Regarding Switch Boxes

  1. #1
    DIY Junior Member winklebe's Avatar
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    Default Silly Question Regarding Switch Boxes

    I am in the middle of a bathroom remodel. As part of the remodel I am changing the swing of the door and will need to move the switches from one side of the door to the other. Not a big task as I am rewiring the room for moved lights fans ect.

    However, when I look at the open wall that the box will be placed in I realized that the Void between the studs were the box will be located is currently being used as a Cold Air Return. The return is basically a vent at the top of the wall and using the studs and drywall as the passage.

    Does anyone out there see an issue with placing the wiring, switches and boxes in the same opening between the studs that is operating as a cold air return?

    Thanks

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    DIY scratch-pad engineer leejosepho's Avatar
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    The air passing by would certainly help keep the electricals cool, but it would also carry sparks to other places and it could even "fan the flame" if something gets too hot ... so I would guess the NEC does not allow that.

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    DIY Junior Member winklebe's Avatar
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    Agreed. What if I partitioned the Cold Air return and built a 2x4 box around the switches and wiring, narrowing the passage used for the cold air return. does any know of a specific requirement for the size of the passage used for the cold air return? I am guessing that its like 14" now and I would have it to about 5" wide .

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    DIY Member Lightwave's Avatar
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    Quote Originally Posted by winklebe View Post
    does any know of a specific requirement for the size of the passage used for the cold air return?
    Each return vent should be sized for the room (or collection of rooms) it serves. A simple rule of thumb is to match the effective cross sectional area of all supply vents in the immediate vacinity of a return vent.

    For example, if you have a room with one 6" round supply duct and one return, the return duct should be 6" or an equvalent rectangular dimension. Note that the equivalent dimensions of rectangular and circular ducting must be properly calculated using an air flow formula rather than with areas calculated with pi*r^2.

    Matching equivalent cross sectional area approximation does not take into account supply dampers or differences in the effective length of the return and supply ducts. To get a definitive answer, an ACCA Manual D calculation is required.

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    Moderator & Master Plumber hj's Avatar
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    IF it is a metal box, and all the openings are closed with plugs or wire connectors, I cannot see how ANY sparks could get out of it, and there would not be enough air to support any combustion inside the box either. IF there could be any problems, there are convection currents inside a stud space that would do the same thing as a return duct.

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    Electrical Contractor Jim Port's Avatar
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    Non-metallic cables are only allowed perpendicular to the return. Running lengthwise is prohibited.

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    DIY Junior Member winklebe's Avatar
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    Thanks for all of the input.

    Jim are you saying that I place the box in the return I can not run the Wires up the stud in the Return unless they are in a metal conduit?

    and if that is the case, would a 2x4 down the middle of the return creating a enclosure mitigate this requirement? or I could move the intake in the adjoining room to a lower placement on the wall and then have all the wiring above the return?

    I guess I am still a little lost..

    Maybe I am asking what would you do in this case?

    Thanks again all.

  8. #8
    Electrical Contractor Jim Port's Avatar
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    I think running a 2x down the wall would remove the wiring from the return and would be NEC compliant. Doing this may reduce the airflow required for efficient operation of the HVAC system.

    I hope this formats correctly. Here is the NEC section.

    (C) Other Space Used for Environmental Air. This section
    applies to space used for environmental air-handling
    purposes other than ducts and plenums as specified in
    300.22(A) and (B). It does not include habitable rooms or
    areas of buildings, the prime purpose of which is not air
    handling.
    FPN: The space over a hung ceiling used for environmental
    air-handling purposes is an example of the type of other
    space to which this section applies.
    Exception: This section shall not apply to the joist or stud
    spaces of dwelling units where the wiring passes through
    such spaces perpendicular to the long dimension of such
    spaces.
    (1) Wiring Methods. The wiring methods for such other
    space shall be limited to totally enclosed, nonventilated,
    insulated busway having no provisions for plug-in connections,
    Type MI cable, Type MC cable without an overall
    nonmetallic covering, Type AC cable, or other factoryassembled
    multiconductor control or power cable that is
    specifically listed for the use, or listed prefabricated cable
    assemblies of metallic manufactured wiring systems without
    nonmetallic sheath. Other types of cables and conductors
    shall be installed in electrical metallic tubing, flexible
    metallic tubing, intermediate metal conduit, rigid metal
    conduit without an overall nonmetallic covering, flexible
    metal conduit, or, where accessible, surface metal raceway
    or metal wireway with metal covers or solid bottom metal
    cable tray with solid metal covers.

    I typically try to work these things out when the building is being roughed in. Can you move the switches over just outside the return?

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