Adding a box extension to increase fill capacity

Reply

  #1  
Old 09-19-05, 04:35 PM
Member
Thread Starter
Join Date: Nov 2004
Location: USA
Posts: 973
Received 0 Votes on 0 Posts
Adding a box extension to increase fill capacity

I have a metal junction box, 4x4x2 1/8, which, per table 314.16(a) is 30.3 cu in and suitable for 13 12G conductors. It has two conduits entering it.

It currently has 4 wires simply passing through it, in one conduit, out another, with no splices (but sufficient wire looped so it could be spliced), three wires entering from a conduit (these are currenty not connected to anything in this box), and a ground wire entering from each conduit (yes, the box is bonded to ground).


I need to add to this box three runs of 12-2wg Romex and a 12-3wg Romex, which obviously puts me over the fill limit. I need to determine how far over I would be, and whether I can simply add a 4 x 1 1/2 square box extension for the extra fill capacity needed. The existing conductors are long enough, even with the extra box depth.

I do not want to replace the box entirely as I'd prefer to leave the four wires alone which pass through unspliced.


Questions:

Do the four wires passing through count once each, or twice each?

A 4 x 1 1/2 square box is 21.0 cu in, or 9 12G conductors per table 314.16(a). When adding an extension, do I simply add these numbers to the original boxes capacity?
 
Sponsored Links
  #2  
Old 09-19-05, 06:44 PM
ampz's Avatar
Member
Join Date: Feb 2004
Location: Philadelphia
Posts: 536
Received 0 Votes on 0 Posts
Each wire passing thru {unspliced} counts as one. Just add the cacity of the extension to the cacity of the original box & caculate fill.
 
  #3  
Old 09-22-05, 11:38 AM
Member
Thread Starter
Join Date: Nov 2004
Location: USA
Posts: 973
Received 0 Votes on 0 Posts
Thanks ampz.

The conductors which passed through the box in question went to another box which was also overfilled (I need only look in the mirror to find the offender), so I needed to make a change there. Since I was taking things most of the way apart, I went ahead and replaced both boxes with larger ones.

The language of 314.16(B)(1) makes me think that those conductors which passed through the box should have counted twice each. It says "A looped, unbroken conductor not less than twice the minimum length required for free conductors in 300.14 shall be counted twice". I believe I had enough looped to have met that requirement. When I redid things, I ended up replacing the conduit with a slightly longer conduit run, so the extra conductor length went away. (I'm glad I left it long the first time!)


As I'm learning about box fill, I'm definately seeing the light on using extra large boxes. I'm starting to lean towards 4 x 2 1/8 square metal boxes as a minimum. I've also learned to be careful to buy the box with the correct size knockouts. It's frustrating when you get home, look at the box, and note that the smallest knockout is 1". Thankfully, home depot is just five minutes away.
 
  #4  
Old 09-22-05, 06:38 PM
ampz's Avatar
Member
Join Date: Feb 2004
Location: Philadelphia
Posts: 536
Received 0 Votes on 0 Posts
Sorry I missed the emphasism on how large the looped conductors were.Always have reducing washers handy{ 1" to 3/4", 3/4" to 1/2"}.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: