What size box for...

Old 10-26-00, 02:59 PM
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10ga. wire, going to have three wire nuts, Each nut will connect 3 10ga. wires.

What size box do I need?
Plastic and/or metal please...

Old 10-26-00, 08:05 PM
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hello pete,
from the info in your post i cant say for sure what size box u need. you stated there will b 3 wire nuts with 3 #10 wires in each totaling 9 #10 wires. u didnt say if there were going to be any devices or internal clamps.
box fill calculation is as follows
# of conductors X 2.5 for #10
each strap for a device adds 2 conductors
each internal clamp adds 1 conductor
grounds count as 1 conductor no matter how many u have.
useing the info in your post as an example
with 1 wirenut being for a ground, and 1 device and 1 internal clamp.
6 x 2.5 = 15 (# conductors not counting grounds)
1 x 2.5 = 2.5 (grounds)
2 x 2.5 = 5 (device)
1 x 2.5 = 2.5 (internal clamp)
15 + 2.5 + 5 + 2.5 = 25
u would need a box of at least 25 cubic inches.
cubic inches for metal boxes can be found in tabel 370-16 a of the nec, this also states max # of same size conductors in a box or can be figured by takeing
length x width x higth. cubic inches for plastic boxes r stamped on the box.
Old 10-26-00, 08:58 PM
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Sparky you did good!

Now I have a concern about the type of connection that he is using to connect 3 - 10 ga. wires. I wanted to point out that the connector used to slice these three 10 ga. wires together must be rated for that many wires of that size.


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