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04-14-2010, 11:18 AM   #1
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## Wiring Junction Box From Scratch

Let's say you want to install a brand new junction box with four cables(all 12/2), one entering the box on each side.

First of all, how much wire should you pull through into the box? Do you need to pull in the same amount for all four cables, or can/should some be shorter.

Also, when connecting wires together, do you just pull them straigt down to line them up or is there another method to that.

Finally, in this case we have of 12 wires in the junction box. How do you know if you exceeding the box fill?

Thanks.
dw1256

 04-14-2010, 11:43 AM #2 Just call me Andrew   Join Date: Mar 2009 Location: Albany, NY Posts: 2,271 Rewards Points: 1,032 Here's a good article on calculating box fill: http://www.selfhelpandmore.com/home-...tions-2002.php I usually have each cable extend about 6-8" out of the box. If the box is metal it must be grounded with a screw or clip. Also, if the box is metal, you need cable clamps at each knockout. If you have four 12-2 cables entering the box, each current-carrying cable (black & white in your case) counts as 1 wire. All the gounds together count as 1 wire. Clamps & fittings all together count as 1 wire. I think this is the proper calculation for your box. Each 12AWG wire takes 2.25 cubic inches. Current-carrying wires: 8 x 2.25 = 18 Ground wires: 1 x 2.25 = 2.25 Clamps: 1 x 2.25 = 2.25 Total Required 22.5 __________________ Andrew Last edited by secutanudu; 04-14-2010 at 11:49 AM.

04-14-2010, 05:08 PM   #3
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Quote:
 Originally Posted by dw1256 Let's say you want to install a brand new junction box with four cables(all 12/2), one entering the box on each side. First of all, how much wire should you pull through into the box? Do you need to pull in the same amount for all four cables, or can/should some be shorter. Also, when connecting wires together, do you just pull them straigt down to line them up or is there another method to that. Finally, in this case we have of 12 wires in the junction box. How do you know if you exceeding the box fill? Thanks. dw1256
we would hypothetically look at the code for your area and that would tell you the length of wires needed inside the box and the box fill numbers(of which 8 conductors will fit in most JB's). Hypothetically of course

 04-14-2010, 05:53 PM #4 Member   Join Date: Jan 2009 Location: South of Boston, MA Posts: 17,248 Rewards Points: 2,000 For me I oversize junction boxes so I don't have to worry about box fill I have some very large junction boxes in the basement that have been there a long time -since house was upgraded to 200a years ago Min size of box will depend upon the wire size I like to leave about 8" of wire for each cable with the larger boxes I pull them to the center & twist them together

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