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Thread: Junction Box

  1. #1
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    Default Junction Box

    I don't have the table for calculating the box size needed for this. It seems to be the right size. What do you think?

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    Tom Rees / A Closer Look Home Inspection / Salt Lake City, Utah

  2. #2
    Robert Meier's Avatar
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    Default Re: Junction Box

    IMO it's almost impossible to overfill a box that size. If this is a wet location the NM cable is not permitted in that raceway. Guessing that it's a 12"x12"x4" box that would be 576 cu inches. For #12 conductors you would need 2.25 cu in per conductor that would be 256-#12 AWG conductors permitted in that box and grounds only count as one conductor.

    Last edited by Robert Meier; 02-21-2012 at 07:11 PM. Reason: Added calculation

  3. #3
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    Default Re: Junction Box

    Thanks Robert, I was almost sure but thanks for the calculation. Could you elaborate on the NM cable in raceway?

    Tom Rees / A Closer Look Home Inspection / Salt Lake City, Utah

  4. #4
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    Default Re: Junction Box

    The use of NM in the raceway is not the issue. The issue is the raceway is outside. Outside is a wet location, NM is not for use in wet locations.

    All answers based on unamended National Electrical codes.

  5. #5
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    Default Re: Junction Box

    Got it. Thanks.

    Tom Rees / A Closer Look Home Inspection / Salt Lake City, Utah

  6. #6
    brianmiller's Avatar
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    Default Re: Junction Box

    Quote Originally Posted by Jim Port View Post
    The use of NM in the raceway is not the issue. The issue is the raceway is outside. Outside is a wet location, NM is not for use in wet locations.
    Are not the JB and conduits shown in the picture rated for exterior/wet locations? We is keying you that they are not?

    b


  7. #7
    Robert Meier's Avatar
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    Default Re: Junction Box

    Quote Originally Posted by brianmiller View Post
    Are not the JB and conduits shown in the picture rated for exterior/wet locations? We is keying you that they are not?

    b
    The problem is when the raceway is installed in a wet location the inside of that raceway is also considered a wet location and NM cable is not permitted in wet locations.

    300.9 Raceways in Wet Locations Above Grade.
    Where raceways are installed in wet locations above grade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations above grade shall comply with 310.8(C).



  8. #8
    brianmiller's Avatar
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    Default Re: Junction Box

    Quote Originally Posted by Robert Meier View Post
    The problem is when the raceway is installed in a wet location the inside of that raceway is also considered a wet location and NM cable is not permitted in wet locations.
    Thanks, Robert.....I understand WHAT you are saying...but I'm not understanding, then, what you are calling a raceway. What is the difference of having the service equipment panel with NM cables inside of it on the exterior of the house/wet location versus the Junction Box in the OPs picture?


  9. #9
    Robert Meier's Avatar
    Robert Meier Guest

    Default Re: Junction Box

    Quote Originally Posted by brianmiller View Post
    Thanks, Robert.....I understand WHAT you are saying...but I'm not understanding, then, what you are calling a raceway. What is the difference of having the service equipment panel with NM cables inside of it on the exterior of the house/wet location versus the Junction Box in the OPs picture?

    In this installation nothing, but according to the NEC NM cables inside of a raceway in a wet location are not permitted. The reason being that raceways in wet locations are subject to moisture on the inside even if they're completely sealed like PVC which is glued together. Since they're subject to moisture a cable or conductor not rated for wet locations can eventually fail.

    In this case the raceway is short section of piping below the LB conduit body.

    One other note if this is under on overhead structure it might not even be a wet location.


  10. #10
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    Default Re: Junction Box

    Quote Originally Posted by Robert Meier View Post
    IMO it's almost impossible to overfill a box that size. If this is a wet location the NM cable is not permitted in that raceway. Guessing that it's a 12"x12"x4" box that would be 576 cu inches. For #12 conductors you would need 2.25 cu in per conductor that would be 256-#12 AWG conductors permitted in that box and grounds only count as one conductor.
    AND you calculate the #10 conductors at 2.5cu in. The grounds will also be calculated at 2.5.


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