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Thread: Nonmetallic box fill question

  1. #11
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    Quote Originally Posted by al hildenbrand View Post
    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.
    True, though most NM cable boxes anymore they are part of the manufactured box. Years ago I remember some fiberglass NM cable boxes we used to get that had a metal screw and clamp you had to install yourself where needed.
    I live for today, I'm just a day behind.

  2. #12
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    Quote Originally Posted by al hildenbrand View Post
    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.

    One has to assume the mention of a clamp means to count it but as I said earlier this is not a good question. At least the OP understands what he needs to look for. You can't always guess what a test writer is looking for.
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  3. #13
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    Quote Originally Posted by kwired View Post
    . . . most NM cable boxes anymore they are part of the manufactured box.
    I believe that the clamps in the Allied line thrust the cable forward into the middle of the box volume, there by eating a chunk of cubic inches behind the stripped wires in the corner against the clamp. . .

    Even though the clamp assembly in the Allied box is "part of the manufactured box" by virtue of being clipped in place, the loss of usable volume requires attention, in my opinion.
    Another Al in Minnesota

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    Quote Originally Posted by al hildenbrand View Post
    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.
    Since it is a test question, I am guessing internal clamps that are part of the box. Who knows?
    "Electricity is really just organized lightning." George Carlin


    Derek

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    Quote Originally Posted by jumper View Post
    Since it is a test question, I am guessing internal clamps that are part of the box. Who knows?
    I agree with your earlier point that, regardless, the NEC guides us to count the "NM box internal factory cable clamps."
    Another Al in Minnesota

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    Quote Originally Posted by al hildenbrand View Post
    I believe that the clamps in the Allied line thrust the cable forward into the middle of the box volume, there by eating a chunk of cubic inches behind the stripped wires in the corner against the clamp. . .

    Even though the clamp assembly in the Allied box is "part of the manufactured box" by virtue of being clipped in place, the loss of usable volume requires attention, in my opinion.
    I use those sometimes, doesn't change usable volume by any significant amount IMO, but I see what you are saying also. I also use P&S plastic device boxes - the clamps in those make almost no change to space within the box when you insert a cable, seems stupid to me to have to count this particular type of clamp they use on that line of boxes.
    I live for today, I'm just a day behind.

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    Quote Originally Posted by kwired View Post
    I use those sometimes, doesn't change usable volume by any significant amount IMO, but I see what you are saying also. I also use P&S plastic device boxes - the clamps in those make almost no change to space within the box when you insert a cable, seems stupid to me to have to count this particular type of clamp they use on that line of boxes.

    I have brought this up many times and no one around here counts that clamp in P&S boxes. The way the code is written I think that they should be counted. IMO, it depends on whether the box volume is based on the interior clear space or whether it includes the clamp space. If it includes the clamp space then one would have to count it.
    They say I shot a man named Gray and took his wife to Italy
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    Quote Originally Posted by Dennis Alwon View Post
    I have brought this up many times and no one around here counts that clamp in P&S boxes. The way the code is written I think that they should be counted. IMO, it depends on whether the box volume is based on the interior clear space or whether it includes the clamp space. If it includes the clamp space then one would have to count it.
    I have posted UL, Carlin, and CMP statements that all say you gotta count the clamps.

    You deduct it from cubic inches or the stamped wire allowance inside the box.

    Nobody does this in real life, only on tests AFAICT.
    "Electricity is really just organized lightning." George Carlin


    Derek

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    BOXFILL ANSWER

    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 ?
    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.
    You count 2 volume allowance for each device, a single volume allowance for the cable clamps, and a single volume allowance for the ground. (Essentially, 2 wires for each device (for the largest wire connected to each device), one wire for the clamps, and one wire for the grounds (per the largest ground in the box) If they are all #14AWG the volume allowance would be 2 cu. in. ADD - 6 cu. in. for the devices, 2 cu. in. for the cable clamps, 2 cu. in. for the grounds - that gives you 10 cu. in. total. 44-10 = 34 cu. in. 34/2 = 17 conductors. If you are using 12/2 w/ gnd Type NM cables then it would be (8) 12/2 / gnd Type NM cables

  10. #20
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    Quote Originally Posted by Eddie_B View Post
    You count 2 volume allowance for each device, a single volume allowance for the cable clamps, and a single volume allowance for the ground. (Essentially, 2 wires for each device (for the largest wire connected to each device), one wire for the clamps, and one wire for the grounds (per the largest ground in the box) If they are all #14AWG the volume allowance would be 2 cu. in. ADD - 6 cu. in. for the devices, 2 cu. in. for the cable clamps, 2 cu. in. for the grounds - that gives you 10 cu. in. total. 44-10 = 34 cu. in. 34/2 = 17 conductors.
    Yup. I agree with your work-up to this point.

    Quote Originally Posted by Eddie_B View Post
    If you are using 12/2 w/ gnd Type NM cables then it would be (8) 12/2 / gnd Type NM cables
    Is this a typo?

    #12 is 2.25 cubic inches per conductor.
    Another Al in Minnesota

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