number of conductors in a box

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  #1  
Old 06-29-13, 01:23 AM
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number of conductors in a box

I want to install 2 12-2 wires and a 20A outlet in a 4 x 2 1/8 x 2 1/8 metal box , bonded.

This is a total of 2 + 2 + 2 ( yoke) + 1 (ground) = 7 conductors . This is greater than NEC 314.16 code of 6.

This just does not seem practical. Many times you just want to go single box to box with just an outlet.

My question is do others violate this rule ?

Please do not respond just follow the NEC code.

Regards,
Robert
 
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  #2  
Old 06-29-13, 07:07 AM
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Your total fill is 20.25". Your box is 30.3". I'm not seeing an issue.
 
  #3  
Old 06-29-13, 08:09 AM
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thanks for the response wirenut110.

First I have a 4 x 2 x 2 box at 14.5 cuin.

next I took 7 conductors x 2.25 = 15.75 cuin.

15.75 is greater than 14.5.

Did I make a mistake in the calculations ?
 
  #4  
Old 06-29-13, 08:24 AM
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I was thinking you had a 4X4 2 1/8" deep. If you have a single gang box with a device then, yes, it's overfill. Your box is 16"


7x2.25=15.75 +4.5 for a device. Total=20.25
 
  #5  
Old 06-29-13, 08:34 AM
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Have to ask...whats a yoke? No electrician, but 12/2 would seem to only be 5 wires, since grounds only count as one. And I also read that wires that don't enter or leave the box (such as pigtails) aren't counted? Saw this exact same question on a search I did...and their calc was 18 (with internal clamps)...which would still be overfill of course.
 
  #6  
Old 06-29-13, 09:10 AM
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The yoke is the mounting strap that holds the device.

Pigtails do not count. Internal clamps do count as one.
 
  #7  
Old 06-29-13, 11:46 AM
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This is a total of 2 + 2 + 2 ( yoke) + 1 (ground) = 7 conductors. This is greater than NEC 314.16 code of 6.

next I took 7 conductors x 2.25 = 15.75 cuin.
This is puzzling. Your logic seems correct:

Table 314.16(A) lists your 4 X 2-1/8 X 2-1/8 in. box as having a minimum volume of 14.5 in.[SUP]3[/SUP] and the maximum number of 12AWG conductors as 6.

Table 314.16(B) requires 2.25 in.[SUP]3[/SUP] of free space within the box for each 12AWG conductor.

In the text:
314.16 Number of Conductors in Outlet, Device, and
Junction Boxes, and Conduit Bodies.
Boxes and conduit
bodies shall be of sufficient size to provide free space for
all enclosed conductors. In no case shall the volume of the
box, as calculated in 314.16(A), be less than the fill calculation
as calculated in 314.16(B).

(B) Box Fill Calculations. The volumes in paragraphs
314.16(B)(1) through (B)(5), as applicable, shall be added
together. No allowance shall be required for small fittings
such as locknuts and bushings.

(1) Conductor Fill. Each conductor that originates outside
the box and terminates or is spliced within the box shall be
counted once,

(4) Device or Equipment Fill. For each yoke or strap containing
one or more devices or equipment, a double volume
allowance in accordance with Table 314.16(B) shall be
made for each yoke or strap based on the largest conductor
connected to a device(s) or equipment supported by that
yoke or strap.

(5) Equipment Grounding Conductor Fill. Where one or
more equipment grounding conductors or equipment bonding
jumpers enter a box, a single volume allowance in accordance
with Table 314.16(B) shall be made based on the largest
equipment grounding conductor or equipment bonding jumper
present in the box.
With two 12-2/G cables and one receptacle, 1 for each conductor = 4, the equipment grounding conductors = 1, and a standard duplex receptacle = 2. That adds up to 7, which is 15.75 in.[SUP]3[/SUP].

That said, it doesn't seem reasonable that this box, which is the largest single-gang device box listed in Table 314.16(A), would be too small to allow the common practice of using two 12AWG cables to feed power in and out and supply one duplex receptacle. As you said,
This just does not seem practical. Many times you just want to go single box to box with just an outlet.
And here's the kicker: I entered this information in a box fill calculator that I've always trusted: Construction Monkey Box Fill Calculations. It said that the total volume requirement is 13.5 in.[SUP]3[/SUP]. and lists a device box measuring 4 x 2.125 x 2.125" is acceptable for this installation.

Maybe we're both missing something.
 

Last edited by pcboss; 06-30-13 at 09:58 PM.
  #8  
Old 06-29-13, 02:32 PM
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Box Fill

Instead of calculating box volume, why not use the box volume stamped inside the box?
 
  #9  
Old 06-29-13, 02:45 PM
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Instead of calculating box volume, why not use the box volume stamped inside the box?
Because that's only stamped inside non-standard boxes and fittings?
 
  #10  
Old 06-29-13, 04:12 PM
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Construction Monkey

Maybe we're both missing something.
The ground wire has to be included in the first info box. The last info box only asks the size of the ground wire.
 
  #11  
Old 06-29-13, 04:26 PM
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The ground wire has to be included in the first info box. The last info box only asks the size of the ground wire.
Good catch! That makes more sense.

OK, that gives 15.8 in.[SUP]3[/SUP] needed and calls for a deep device box: 3 x 2 x 3.5"
 
  #12  
Old 06-29-13, 09:51 PM
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Thanks for the help ...

Thanks everyone for the advice ....
 
  #13  
Old 06-29-13, 10:35 PM
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You're welcome. Sorry about the confusion.
 
  #14  
Old 06-30-13, 06:02 AM
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I don't know why in the heck I was thinking you had 3 cables coming in to your box.

Sorry for the misinformation. Sucks getting old.
 
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