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Thread: Nonmetallic box fill question

  1. #1
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    Nonmetallic box fill question

    Came across the following question: A 3 gang nonmetallic box, with devices is marked 44 CU. IN. The box is equipped with cable clamps.
    How many # 14 AWG 2/C w G NM cables are permitted to enter the box ?
    In Table 314.16 (B) it shows each # 14 requires 2". 44/2 = 22 conductors, each cable has 2 conductors plus ground. Do I count the ground as a conductor resulting in 3 conductors per cable? If this is the case, 22/3 results in 7 cables? Lastly, do I account for the cable clamps?
    I'm studying to take the Virginia master electrician's exam & going through as many test questions as possible.

  2. #2
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    You count the grounds one time and the cable clamps one time. Bad question because are you to presume there are devices in the box?
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  3. #3
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    10- 14/2 cables = 20 conductors x 2 = 40

    grounds and clamps count as 2---- 2x2 = 4

    Total 44
    They say I shot a man named Gray and took his wife to Italy
    She inherited a million bucks and when she died it came to me
    I can't help it if I'm lucky



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    Quote Originally Posted by Dennis Alwon View Post
    You count the grounds one time and the cable clamps one time. Bad question because are you to presume there are devices in the box?
    Whether there are devices, is unclear. So allocate a single quantity for all grounds [1] and another single quantity for for all clamps [1]?

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    So I just count 1 for all the grounds & another 1 for all the clamps ?

    Thanks !

  6. #6
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    Quote Originally Posted by chicagosparky View Post
    So I just count 1 for all the grounds & another 1 for all the clamps ?

    Thanks !
    Yep-- look at 314.15 in the nec
    They say I shot a man named Gray and took his wife to Italy
    She inherited a million bucks and when she died it came to me
    I can't help it if I'm lucky



  7. #7
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    Quote Originally Posted by chicagosparky View Post
    Came across the following question: A 3 gang nonmetallic box, with devices is marked 44 CU. IN. The box is equipped with cable clamps.
    How many # 14 AWG 2/C w G NM cables are permitted to enter the box ?
    Quote Originally Posted by Dennis Alwon View Post
    Bad question because are you to presume there are devices in the box?
    The question, as written above, does not say how many devices, but it does say there are devices which means more than one. I'd answer for three devices because of three gangs (how often have you seen a device-device-blank in a three gang?).

    From 314.15, each device counts as "two conductors".
    All the Equipment Ground Conductors, together, count as only "one conductor".
    All the cable clamps, together, count as only "one conductor."
    Each individual current carrying conductor counts as "one conductor."

    From the question, all the conductors are #14 gauge which is two cubic inches per conductor. Therefore:

    3 - Devices = 3 (device) x 2 (conductors / device) x 2 (cubic inches / conductor) = 6 cubic inches
    All EGCs = 1 (conductor) x 2 (cubic inches / conductor) = 2 cubic inches
    All cable clamps = 1 (conductor) x 2 (cubic inches / conductor) = 2 cubic inches
    __________________________________________________ ______________________
    Total = 10 cubic inches used by devices, EGCs and cable clamps, which leaves 34 cubic inches from the box volume of 44 cubic inches.

    34 cubic inches divided by 2 cubic inches per #14 conductor = 17 conductors.

    To get the maximum cable count in this assembly, note that all the cables are # 14 AWG 2/C w G NM. The black and white are the current carrying conductors, and there are two per cable. "Two" goes into 17 eight and one half times.

    Therefore, the answer is "eight cables."
    Another Al in Minnesota

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    I don't know if right or wrong, but I never count clamps on non metallic boxes, I have always figured they were factored into the count/volume listed on the box. Not like you typically have an option to remove or not use them either like you may have on other box types.
    I live for today, I'm just a day behind.

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    Quote Originally Posted by kwired View Post
    I don't know if right or wrong, but I never count clamps on non metallic boxes, I have always figured they were factored into the count/volume listed on the box. Not like you typically have an option to remove or not use them either like you may have on other box types.
    Nobody counts the clamps, but you are supposed to count them.
    "Electricity is really just organized lightning." George Carlin


    Derek

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    Quote Originally Posted by kwired View Post
    I don't know if right or wrong, but I never count clamps on non metallic boxes,
    The question, as written in the OP, does not say if the cable clamp is part of the manufactured box, or if the cable clamp is a snap in clamp in a K.O.
    Another Al in Minnesota

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