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I'm running three 8awg THHN thru 1/2" sch-40 to garage, attaching same to existing 10awg NM-B at a J-box TBD in basement ceiling. I may change 10 to 6awg in future. So my questions are ..

  1. metal or plastic j'box, how to join wires internally.. alt for wire nuts ? Something like this but this is aluminum .. is there a copper version that's similar?

  2. read that THHN wire is NOT suitable for "wet" locations. My conduit will be inside wall until inside garage, is this considered wet? Also wire markings indicate this is also THWN so assume this is a non-issue .. please comment and/or confirm.

Thanks, Ron

Ron C
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  • Metal or plastic boxes are both allowed. Some people prefer metal over plastic, for grounding and fire resistance. A garage attached to the house should be consider inside/dry location. – crip659 Feb 25 '23 at 16:43

2 Answers2

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As already answered, check the labels but your wire is probably fine.

Metal vs. plastic? Almost always metal is better.

10 AWG to 6 AWG or 8 AWG? Ideal makes wire nuts that will work - e.g., WT54 Blue or 66 Gray/Dark Blue or B4 Blue/Gray.

manassehkatz-Moving 2 Codidact
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Virtually all modern THHN is also marked as THWN or THWN-2, and possibly also MTW or other grades. So long as one of the several grades is wet, it would be fine if it needed to go outside, but for a connection to an attached garage, not run on the outside of the building, the conduit is a dry location anyway.

Ecnerwal
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  • Thanks, any thoughts on best practice to join 10 & 8 and 8 & 6 awg or box type preference ? I'm leaning toward plastic .. conduit ready, non-conductive, and since I'm using bare ground-to-insulated green for EV charger, white will be dead ended in the box (not used). – Ron C Feb 25 '23 at 19:32