Nonmetallic box fill question

[chicagosparky]

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.

 

[Dennis Alwon]

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?

 

[Dennis Alwon]

10- 14/2 cables = 20 conductors x 2 = 40

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

Total 44

 

[chicagosparky]

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]?

 

[chicagosparky]

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

Thanks !

 

[Dennis Alwon]

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

Thanks !

Yep-- look at 314.15 in the nec

 

[al hildenbrand]

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 ?

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."

 

[kwired]

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.

 

[jumper]

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.

 

[al hildenbrand]

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.

 

[kwired]

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.

 

[Dennis Alwon]

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.

 

[al hildenbrand]

. . . 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.

 

[jumper]

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?

 

[al hildenbrand]

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."

 

[kwired]

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.

 

[Dennis Alwon]

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.

 

[jumper]

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.

 

[Eddie_B]

BOXFILL ANSWER

BOXFILL ANSWER

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

 

[al hildenbrand]

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.

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.