box size


Old 01-09-08, 10:46 PM
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box size

What is the rule of thumb (code) for what size junction box is needed for 10-conductors (12 wire thhn). Also when making the connections are the connected wires counted as one or is it each wire that enters the box counted as one conductor. I plan on connecting THHN to romex to each circut which would then make it 5 thhn hot wires, 5 thhn neutral, 1 thhn ground, and 5-12/2 entering the same box. These connections will all be made in an attic, into a junction box (preferably plastic) with a blank cover.
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Old 01-09-08, 11:33 PM
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each #12 wire need 2.25 cubic inches in the box and what you have there :

5 thhn hot wires= 11.25 cubic inches
5 THHN white wire = 11.25 cubic inches
1 THHN ground wire = 2.25 inches

each 12-2/G NM required 6.75 cubic inches each so you have 5 of them so it will come out 33.75 cubic inches

33.75 + 11.25 + 11.25 + 2.25 = 58.5 cubic inches so you need a box that have at least 60 cubic inches or larger.

if my figures are wrong let me know escpally on ground wire part i am not sure if that nailed right.

but i did not include the romax clamp but they do count as well on metal box.

for that many wire i will like to use 4 11/16 deepwell box or larger [ some call 5X5 box ] or you can use the 6X6X4 box that will easly meet the fill wise.

if other pro feel my figures are wrong let me know [ i am used to figures with metric sized wires and boxes and larger standard wires as well ]

Merci, Marc
Old 01-10-08, 05:23 AM
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Marc, your figures are wrong, due to the grounds. Forget the fact that it is 12-2, and count each wire properly.

20 current carrying conductors and 1 ground. That makes 21 wires to figure for. That means 47.25 cubic inches forr the wires.
Old 01-10-08, 11:35 AM
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Thanks Racraft for correcting me on mixed bags.

for some reason i was look like this > after a long day on my work.

i will remember that next time and thank again.

Merci, Marc

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