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  1. #1
    Join Date
    Jun 2009
    Posts
    19

    Default Calculating Wires Allowed in Electrical Boxes

    Hello All,

    I'm trying to determine if any the boxes I've wired have too many wires. I am using all plastic boxes and 12 gauge NM wire with no clamps. This is how I'm calculating the allowed number of insulated wires allowed for the boxes I'm using. Please let me know if my method of calculating allowed insulated wires is correct??

    Example 1:
    =========
    Double Gang Switch Box (34 CUI) --> 34/2.25 = 15 wires allowed. Now subtract 1 wire for the ground & 2 wires for each switch (2*2 = 4) = 10 insulated wires allowed.

    Example 2:
    =========
    Single Gang Switch Box (22 CUI) --> 22/2.25 = 9 wires allowed. Subtract 1 ground - 2 wires for the switch = 6 insulated wires allowed.

    Example 3:
    =========
    Ceiling Box (25 CUI) --> 25/2.25 = 11 wires allowed. Subtract 1 for ground = 10 insulated wires allowed.

    Thanks,

    Chris

  2. #2
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,775

    Default Re: Calculating Wires Allowed in Electrical Boxes

    See attached
    Jack
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    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  3. #3
    Join Date
    Jun 2009
    Posts
    19

    Default Re: Calculating Wires Allowed in Electrical Boxes

    JLMCDANIEL,

    None of my boxes in the table you posted correspond to the box CI's I have installed. Is my calculation based on the box CI correct?

    Regards,

    Chris

  4. #4
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,775

    Default Re: Calculating Wires Allowed in Electrical Boxes

    Yes, your calculations appear to be correct for the CUI you listed.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  5. #5
    Join Date
    Mar 2009
    Posts
    1,387

    Default Re: Calculating Wires Allowed in Electrical Boxes

    Howdy, Are you including the ground wires in your rule of thumb? And are ya counting the wire nuts?

  6. #6
    Join Date
    Jun 2007
    Location
    Shamokin, Pa.
    Posts
    645

    Default Re: Calculating Wires Allowed in Electrical Boxes

    Quote Originally Posted by Timothy Miller View Post
    Howdy, Are you including the ground wires in your rule of thumb? And are ya counting the wire nuts?
    Remember to include the devices when you calculate your total.

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