Outlet Box Volumes

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  #1  
Old 10-03-06, 12:50 PM
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Outlet Box Volumes

I have two conditions that I am working on:

1st. CONDITION:

Install a new 12A,120v circuit (12/2wg,NM-B) to an "existing"
2"x3"x2-1/2"D flushed in metal box.
Provide a new 20A duplex receptical.

After reviewing the NEC (Article 370.6(a) Standard Boxes and Table 370-6(a) Metal Boxes) it appears that the "existing" box will have enough volume for the number and size of the conductors, internal clamps and receptacle.

Am I correct in my code interpretation?



2nd. CONDITION;

Install a new 12A,120v circuit (12/2wg,NM-B) to a "new" first floor box. Then extend the circuit from this box to a "new" box on the second floor. Both boxes to be flushed in and to be metal. Each box to have a 20A duplex receptacle.

After reviewing the NEC (Article 370.6(a) Standard Boxes and Table 370-6(a) Metal Boxes) it appears that a 2"x3"x3-1/2"D box on the first floor will have enough volume (for the number and size of the conductors, internal clamps and receptacle) to allow me to extend the circuit from this box to the second floor box.

Am I correct in my code interpretation?

This may sound elementary to most.
I just want to make sure that I am interpreting this portion of the code correctly.

Your comments would be appreciated,
Thanks Bob
 
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  #2  
Old 10-03-06, 01:09 PM
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bdek,
welcome to the forum. that was a detailed explaination of what you have going on, but you missed one very important point.

How many of what size wires do you have in each box.???

That is what the box fill calculations depend on.
 
  #3  
Old 10-03-06, 03:57 PM
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Outlet Box Volumes (fill)

jwhite,

Thanks so much for your response.
I apologize for not giving you the exact information.

1st. CONDITION:

Cable into the existing box: 12-2wg NM-B
(1)Duplex Receptacle: 12A/120v
Box fill: (3) conductors/wires

Will the existing box (2"x3"x2-1/2"D) with clamps handle the fill?


2nd. CONDITION:

Cable into box: 12-2wg NM-B
(into first floor out to second floor)
(1)Duplex Receptacle: 12A/120v
Box fill: (6) conductors/wires

Will a 2"x3"x3-1/2"D box with clamps handle the fill?

Thanks again Bob
 
  #4  
Old 10-03-06, 04:22 PM
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You need to tell the number and size of the wires in the existing box in condition 1.

For condition 2 you would have 7 wires. 2 in, 2 out, 2 for device, and 1 ground. 7x2.25=15.75 cu in. This does not count the clamp volume which would equal one more at 2.25 for a total needed volume of 18 cu in.
 
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Old 10-03-06, 10:05 PM
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Outlet Box Volume (fill)

pcboss,

Thanks for the help. Now have a better understanding of how to calculate the fill volume for a box. Also doesn't help to have old incomplete references.

1st. CONDITION (revised)

Have existing flushed 2"x3"x2-1/2" metal box with (2) clamps.
(empty abandoned box @12.5cu in.)

Would like to provide:
Cable to box: 12-2wg NM-B
(1) Duplex receptacle: 12A/120v


Volumes required:

2 for wires in
2 for device
1 for ground
1 for clamps

Total: 6 wire volumes x 2.25 = 13.5 cu in
Therefore I would need to replace the existing box
@ 12.5 cu in with either a 14 or 18 cu in box.

or

Can I remove one of the clamps to reduce the clamp
volume to 1.12 cu in? This would reduce the total
required wire volume from 13.5 to 12.38 cu in in the
box. I would then be able to to use the existing 12.5
cu in box for the project.

Again I would appreciate your comments,
Thanks Bob
 
  #6  
Old 10-04-06, 05:04 PM
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Box volume requirements

NEC 2005, Article 314.16
Clamp volume is based on largest wire present.
 
  #7  
Old 10-05-06, 05:44 PM
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Outlet box volumes (fill)

1st CONDITION:
I have changed out the box to 18 cu in. - - which is required.

Thanks everybody for all the responses. I have learned a lot with this project.
Great forum on Do It Yourself.com
Bob
 
  #8  
Old 10-07-06, 10:54 PM
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Technically, you don't need to count the ground wires, or any pigtails.

Here's a quick table on the maximum number of individual wires in a box. (Again, don't count pigtail or grounding wires.)


Box Shape Box Depth 14-gauge 12-gauge
2"x3" 2 1/2" deep 3 3
rectangle 3 1/2" deep 5 4

4"x4" 1 1/2" deep 6 5
square 2 1/8" deep 9 7

Octagon 1 1/2" deep 4 3
2 1/8" deep 7 6

Best wishes.
 
  #9  
Old 10-08-06, 07:58 AM
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"Technically, you don't need to count the ground wires, or any pigtails."

314.16 (A) (5) disagrees with you regarding the ground wires.
 
  #10  
Old 10-09-06, 12:02 AM
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Hi jwhite,

Thanks for the correction, and my apologies to anyone I may have misled.

I got the information I quoted from a book called, "The Complete Guide to Home Wiring", p. 36, and published under the auspices of Black&Decker, in 2005.

A few other notes:

I've ordered the new 2005 edition of the NEC, and it should arrive early next week. After this, I think I'll just use the "bible" rather than risk getting it wrong again.

I have been consulting the online 2005 edition of the NEC, and I couldn't find 314.16(A)(5). I didn't look at the 2002 or earlier editions, so the reference could be in one of those versions. Here's the link:

http://www.nfpa.org/freecodes/free_access_document.asp


Thanks again!

Rick
 
  #11  
Old 10-09-06, 03:15 AM
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my fault it is (B) (5)
 
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