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How do i run conduit from plastic outside jb to inside metal jb through wall?

How do i run conduit from plastic outside jb to inside metal jb through wall?

Old 07-24-18, 11:46 AM
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Question How do i run conduit from plastic outside jb to inside metal jb through wall?

I have a deck, it's completely covered, waterproof and has 3 3/4 walls and a little area to squat through to get underneath, it attaches to the back of the house and the basement is visible through a window. I want to cut the female end off a 10 AWG extension cord and run it into a box under the deck on the house, waterproof I assume, (it would be easier if it wasn't - you'll see in a minute) and then join it to 10 AWG THHN in the box which will run through the wall, in conduit of some kind and into a box inside - most likely or directly into a sub box where it will attach to a breaker.

I'm unsure how to connect EMT conduit, if I use that, to the outside weatherproof junction box, and likewise if I use LT flexible conduit how to attach that to a metal box inside? It would be easier for me to use the EMT given a 90 turn inside I'll need to make.

Thanks very much,


The photos show the outside starting point and the inside point. Someone had previously put some UF through a hole to power a GFCI and light under the deck (both in waterproof boxes).
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Old 07-24-18, 12:24 PM
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Forget the extension cord idea. You can just drill through the ledger joist and run UF-B cable from indoors to outdoors. Drill a 1/2" or 5/8" hole and seal up with silicone caulk or foam. The UF can run through holes bored in the deck framing just like Romex inside the house. The UF can be sleeved in conduit if you want but it is not required in a protected area like the underside of the deck. There are UF box fittings for exterior Bell boxes.

It's not the best practice to mix metal and plastic conduit parts because you break the continuous grounding path and potentially create an "island" of ungrounded metal. It can be done, but cautiously.

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