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Thread: Pancake Box Fill

  1. #11
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    Quote Originally Posted by electrofelon View Post
    I like the allied molded boxes the best, but have to resort to the blue bombers frequently. There have been some discussions on the clamps in NM boxes and I thought the general consensus was that they dont count as clamps? I usually just look at the volume and do my own calc. I know they often have the number of conductors also molded in but just habit I guess I do my own calc.
    No, the general consensus is that no one cares.

    UL, Carlton, and the NEC CMP all say you gotta deduct the clamps from the marked volume but it pretty much never ever happens and prolly never will. Inspectors don’t care or bother either.

    But jumper knows the truth...worthless info, but technically correct.
    "Electricity is really just organized lightning." George Carlin


    Derek

  2. #12
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    Quote Originally Posted by jumper View Post
    No, the general consensus is that no one cares.
    thanks for the correction
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  3. #13
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    Deduct clamps from marked volume and a 27.5 cu in 2 gang box with 8 possible entries, using only 14 AWG cables -

    16 cubic inches are taken up by clamps.

    4 cubic inches are taken up by devices.

    7.5 cubic inches are left for conductors - that limits you to entering that 2 gang box with only one 14-2 cable.

  4. #14
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    Quote Originally Posted by kwired View Post
    Deduct clamps from marked volume and a 27.5 cu in 2 gang box with 8 possible entries, using only 14 AWG cables -

    16 cubic inches are taken up by clamps.

    4 cubic inches are taken up by devices.

    7.5 cubic inches are left for conductors - that limits you to entering that 2 gang box with only one 14-2 cable.
    Um, you do know that all the clamps count as one conductor like EGCs.........

    314.16(B(2)
    "Electricity is really just organized lightning." George Carlin


    Derek

  5. #15
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    Quote Originally Posted by jumper View Post
    Um, you do know that all the clamps count as one conductor like EGCs.........

    314.16(B(2)


    Oops.

    Still significant enough reduction there is only room for three 14-2 in that 2 gang box.

  6. #16
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    Quote Originally Posted by kwired View Post


    Oops.

    Still significant enough reduction there is only room for three 14-2 in that 2 gang box.
    A 27.5cu in 2 gang box w/internal clamps, 2 devices, and all 14ga wire:

    2 cu in deduction for all clamps
    8 cu in taken by devices
    that's 10 cu in, leaving 17.5cu in left. That's 8 conductors, 7 + all grounds, gives 3 14/2 as you say, or two 14/2 and a 14/3, remainder 1.5 cu in. However, isnt one allowed rounding up here, or no?

    27.5cu in for a 2 gang is pretty small; many are 34-38cu in.

    Back to the original question, I've no problem running a single 12 or 14/2 to a pancake box regardless of its marked capacity. The 314.16(B)(1) exception is what I was thinking as well for omitting the ground.

    I too hate pancake boxes but sometimes you have to put a box right on a stud or joist, like sconce lights in bathrooms. If possible, i'll use something like an arlington box that has box capacity on the side of the lumber

    ETA: I do not consider those heavy duty plastic tabs in carlon boxes as internal clamps. Now, a butterfly clamp in a metal box one screws down on top of NM, yes.
    Electricians do it until it Hertz!

  7. #17
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    Quote Originally Posted by JFletcher View Post

    ETA: I do not consider those heavy duty plastic tabs in carlon boxes as internal clamps. Now, a butterfly clamp in a metal box one screws down on top of NM, yes.
    Isnt that what it comes down to - if those plastic tabs are clamps or not?
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  8. #18
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    Quote Originally Posted by electrofelon View Post
    Isnt that what it comes down to - if those plastic tabs are clamps or not?
    Not as far as pancake boxes go. Switch boxes, like these:

    https://www.homedepot.com/p/2-Gang-3...FUsFDAod7SsH_A

    I count the clamps.

    This plastic box with a side clamp inside:

    https://www.homedepot.com/p/2-Gang-3...ADJC/202197929

    I also count the clamp

    This kind, as well as the flimsier carlon boxes with the little wings that dont really clamp:

    https://www.homedepot.com/p/1-Gang-2...120R/202199225

    I DONT count those, nor do I count the large mounting and device screw bosses against box fill on arlington boxes like these:

    https://www.homedepot.com/p/Madison-...SB1G/203340257

    My methods may not be directly up to the letter of the code but I very seldomly if ever come close to maxxing out box fill in new work. I dont like smashing wire back in the box or having to tear it out/replace it if i need to pull a feed from it.
    Electricians do it until it Hertz!

  9. #19
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    I still feel that counting the clamps in NM boxes is left over from the days when the clamps were separate items screwed into the back of the boxes. It does not make sense that the manufacture would remove the molded clamps to calculate box fill. They are just think pieces of plastic covering the ko that do not take up any room. With screw in clamps the clamps are added after the box is manufactured and volume measured so there is definitely more room with the clamps removed.
    Curt Swartz
    Electrical Contractor

  10. #20
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    Quote Originally Posted by electrofelon View Post
    Isnt that what it comes down to - if those plastic tabs are clamps or not?
    Quote Originally Posted by curt swartz View Post
    I still feel that counting the clamps in NM boxes is left over from the days when the clamps were separate items screwed into the back of the boxes. It does not make sense that the manufacture would remove the molded clamps to calculate box fill. They are just think pieces of plastic covering the ko that do not take up any room. With screw in clamps the clamps are added after the box is manufactured and volume measured so there is definitely more room with the clamps removed.
    Quote Originally Posted by JFletcher View Post

    ETA: I do not consider those heavy duty plastic tabs in carlon boxes as internal clamps. Now, a butterfly clamp in a metal box one screws down on top of NM, yes.
    The push in tabs are clamps.

    Carlton, UL, and CMP all say so.

    I have posted the info before and could go find again, PITA but doable.

    Do you think think I would be crazy enough to assert such a statement about the clamps if I could not back it up? Here of all places?

    No one deducts those including me, but you all wanna push it I would be happy do oblige and prove it later.

    Who is feeling lucky?
    "Electricity is really just organized lightning." George Carlin


    Derek

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