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junction box capacity

| Posted in Energy, Heating & Insulation on January 26, 2004 01:16am

I’m going to install a new Tamarack whole house fan.  I want to replace the single gang box to the hall light with a new double gang “old work” box to hold the light switch and the fan timer.

The fan timer is around twice the volume of a typical single pole switch.  How many 12 and 14 gauge wires can I fit into double gang “old work” box?  Fan requires two hot leads ( one extra for powered doors) and I’d like to someday get a new furnace and make 3-way switch w/ the fan and furnace (code req’d here).  So box volume and wire capacity may be my problem in terms of a cleaner look and code violations.

Thanks for all help.

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  1. User avater
    BillHartmann | Jan 26, 2004 04:04am | #1

    If you look on the main FHB web page there is an article that gives the specifics of figuring box fill. It is simple, but I don't want to bother repeating it. Each yoke is counted as 2 units. They don't make any distictions between a simple device and a "fat one" like a GFCI.

    You need to check the volume of the old work box. If it is plastic it is mold in the box.

    If that is not big enough you can get the extra deep plastic boxes. If I understand this correctly it is replacing an existing box so you are up against the stud. Cut the "flanges" off that hold the nail and put the box in place and then run some screws from the inside of the box into the stud.

    1. AdamB | Jan 29, 2004 03:40pm | #2

      what kind of screws was that.... the black sheetrock Piffin screws? or the gold general construction type?

      1. User avater
        BillHartmann | Jan 29, 2004 05:20pm | #3

        If it is grand home building you use the gold plate GRK screws.

        If it is find home building you use the ordinary gold construction screws.

        If it is average home buinding then you use the Piffin screws.

        Actually for something like this SR screws are fine or whatever you have.

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