box fill for metal 42 cu in box

Discussion in 'Electrical Forum discussion & Blog' started by Antonio4791, Jul 6, 2011.

  1. Antonio4791

    Antonio4791 New Member

    Messages:
    11
    Location:
    South Pasadena CA
    Hi all,

    I'm adding 4 new circuits to my main panel for a kitchen remodel. To get the new wires from the panel into my house, I added a new conduit from the panel which enters into my crawl space. The new conduit goes to a junction box. I will have 4 hots, 4 neutrals and 4 grounds coming into this box, via the conduit (1 inch EMT). Going out of the junction box I will have 4 romex cables (going to the 4 new circuits).

    I have a 42 cubic inch metal box. There is nothing in the box other than spliced wire and wire nuts. I think this should be OK. Here is my calculation:

    I have 8 hots, 8 neutrals and 8 grounds in the box. The grounds as a whole count as one conductor. The 8 hots and 8 neutrals add to 16 conductors. That's a total of 17 conductors. To my knowledge each 12 awg wire counts as 2.25 cu inch. So I have 17 x 2.25 = 38.25. So I think I should be fine. Can someone confirm this.
  2. BobL43

    BobL43 DIY Senior Member

    Messages:
    1,792
    Location:
    Long Island, NY
    This one interests me as well:)
  3. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    Your math is correct.
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,647
    Location:
    Cave Creek, Arizona
    My chart calls a # 12 = 2.62 cu.in. which would make you a bit undersized, but in the real world it probably does not make a big difference.
  5. jbfan74

    jbfan74 Electrical Contractor

    Messages:
    131
    Location:
    Newnan, GA
    You could have used one ground wire from the panel, but the math is correct, just like Mike said.
  6. Antonio4791

    Antonio4791 New Member

    Messages:
    11
    Location:
    South Pasadena CA
    thanks

    Thanks guys. I'll continue with my plan.

    Now I will have everything on dedicated circuits.
  7. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    The NEC allowance for #14 is 2 CI, for #12 2.25 CI.
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