Junction box question

wtonduMarch 28, 2012

In my motorhome I have a standard sized junction box (with cover) that has three 12/3 AWG romex runs in it. All three are wires are tied together - three grounds together, three white together and three black tied together with Wire nuts. All are 120V feeds.

I need to install another junction box adjacent to this one with an electrical outlet. I want to add a 12/3 nomex run from the existing junction box to the new junction box / outlet.

My question is can I splice a fourth 12/3 wire in the original junction box? Do I just need to use next size up wire nuts? There is room in the box. What is the proper way to splice 4 12/3 AWG wires? Should I even have four leads in a box at all?

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randy427

What you have are 12/2 cables (if you are positive they're not 14/2) The ground wire does not count as a conductor in classifying this cable.
There are many 'standard' sizes of junction boxes. You'll need to know the volume of yours.
For #12 conductors, you need 2.25 cu in of box volume for each conductor. (For #14, it's 2 cu in) You currently have 7 conductors (only one of the grounds count) and want to increase it to 9.

    Bookmark   March 28, 2012 at 10:47PM
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wtondu

Assuming the junction box is big enough, what's the proper way to connect the wires? Just use a bigger wire nut?

    Bookmark   March 29, 2012 at 11:38AM
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brickeyee

Wire nut allowed combinations are printed on the side of the 100 box of Ideal wire nuts.

    Bookmark   March 29, 2012 at 3:48PM
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Ron Natalie

Or you can use this, courtesy of our fine friends at Ideal Industries

Here is a link that might be useful: Listed Wire Combinations

    Bookmark   March 30, 2012 at 10:50AM
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randy427

Or you could try the push-in connectors on page 15 of the catalog below.

Here is a link that might be useful: Ideal Push-In Connectors

    Bookmark   March 30, 2012 at 8:04PM
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brickeyee

"Or you could try the push-in connectors on page 15 of the catalog below."

Wait till you see the price per connective.

    Bookmark   March 31, 2012 at 9:07AM
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