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Hello- I have had a hard time finding any direction on this box fill question. Any help will be much appreciated. The questions reads:

I have a 4 x 1 1/2" square box with (4) 14-2's, (1) 14-3 with separate cable clamps. If I add a 4 x 1 1/2" extension how many 12-2's can be added?
A. 0
B.1
C.2
D.3

*** how do you calculate the cubic inches of the extension if it is not listed? Do you double the box size of the original box being it is the same size? Or can you not use it because the cu in is not listed?
Any direction would be helpful. Thanks! 2. Wouldn't a 4" sq box extension have the same cu in as the box itself with the same depth?

Obviously, that is not what they are looking for so I am guessing that you cannot use the volume without having the cu in info.

This is a poor question IMO.
Last edited by Dennis Alwon; 04-11-18 at 07:23 AM. Reason: Change to 4" sq. box 3. Wind kind of cable, does it have an EGC? I would use 2X of the 1900 box volume, calculate the exiting cables and see how much volume is left for the additional cables.  5. I have a 4 x 1 1/2" square box with (4) 14-2's, (1) 14-3 with separate cable clamps. If I add a 4 x 1 1/2" extension how many 12-2's can be added?
A. 0
B.1
C.2
D.3
You're allowed 10-#14's in the box without the extension collar which already over-filled. Use the information from T314.16 to calculate the volume of the box with the collar. Use the cubic inch area of the box to find the area of the collar. 6. Junior Member
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Its type nm cable. I originally started calculating it as a box fill question. I used 21 cu. in. from chart 314.16(A). Then I calculated (4) 14-2's and (3) 14-2's. Which would be 11 conductors plus clamps and ground would make it 13x 2.00=26cu in... then adding the extension which is not stated in question or listed under table 314.16 (A) do you double the cu. in of the box? to make it 42 cu in.? If so... then I would approach it like this.
I would remove the clamp and the ground that is factored into the 26 cu in before adding the extension and multiply those by 2.25 instead of 2.00. to make the total 26.50. Then each 12-2 added would account for 4.5 cu. in. (2 conductors x 2.25 = 4.5cu in) .....Take 42 cu. in. minus the 26.50 =15.5 available cu. in. to be filled. 15.5 divided by 4.5 = 3.4- 12.2's that could be added. So my answer would be 3.

Does anyone follow this or does it make sense? or am I totally lost?

The question might have stated (3) 14-2's not 4 the more I think about it. Either way it wouldn't factor into my reasoning above.

Thank you. 7. That is exactly what I did when I gave my answer of 3 also. 8. Originally Posted by lfobbe2 Its type nm cable. I originally started calculating it as a box fill question. I used 21 cu. in. from chart 314.16(A). Then I calculated (4) 14-2's and (3) 14-2's. Which would be 11 conductors plus clamps and ground would make it 13x 2.00=26cu in... then adding the extension which is not stated in question or listed under table 314.16 (A) do you double the cu. in of the box? to make it 42 cu in.? If so... then I would approach it like this.
I would remove the clamp and the ground that is factored into the 26 cu in before adding the extension and multiply those by 2.25 instead of 2.00. to make the total 26.50. Then each 12-2 added would account for 4.5 cu. in. (2 conductors x 2.25 = 4.5cu in) .....Take 42 cu. in. minus the 26.50 =15.5 available cu. in. to be filled. 15.5 divided by 4.5 = 3.4- 12.2's that could be added. So my answer would be 3.
You are correct. The extension box volume would fall under 314.16(A).

314.16(A) Box Volume Calculations. The volume of a wiring enclosure (box) shall be the total volume of the assembled sections and, where used, the space provided by plaster rings, domed covers, extension rings, and so forth, that are marked with their volume or are made from boxes the dimensions of which are listed in Table 314.16(A).  Posting Permissions

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