My neighbor asked me to help him run power from his breaker panel to his shed out back adding two outlets and two lights. I added a 20 amp breaker and pulled #10 wire from the shed to the house in 3/4 conduit and in a junction box about ten feet inside the attic I transitioned from thhn #10 to NM-B cable and added the 20 amp service breaker.

Everything worked fine but my concern is should there be more to the transition than a box and some wire nuts?


Assuming it's like you describe, and you've done the work to code, that sounds fine. With #10 you certainly won't have to worry about voltage drop.

I trust your THHN wire is also rated THWN-2. Most is.

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    I believe the Romex should also be clamped to the box as a form of strain relief, but many plastic boxes have that built-in. – Hari Ganti Mar 20 '17 at 17:53

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