Best practice for connecting 1/2" metal conduit to 3/4" PVC conduit using a box, in a wet location.


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I am connecting my shed to a 110V 15A GFCI-protected circuit. The wire on the side on the house is THWN inside 1/2" metal conduit. The wire going to the shed is UF-B buried direct and protected by 3/4" nonmetallic (PVC) conduit protecting the UF-B where is it above ground. This is all standard code-compliant stuff and I don't have any questions on that part. My questions are about how to connect these two conduits using a weatherproof box.

I need to connect the THWN that is inside the 1/2" metal conduit to the UF-B that is inside the 3/4" nonmetallic conduit before it goes underground. I will do this inside a weatherproof box attached to the side of the house. The box will have the 1/2" metal conduit connected to the box on the top, and the 3/4" PVC conduit connected on the bottom. I would prefer to use a metal weatherproof box, but a PVC box would be OK if it's code compliant.

Questions:
1. Metal weatherproof boxes have all 1/2" threaded holes OR 3/4" threaded holes. So, the first question is, which one to use? Whichever I uses, I would have to use some sort of adapter for one of the conduits.
2. If I use a metal box with 3/4" threaded connections, the 3/4" PVC conduit is easy to connect. Can I use a 3/4" to 1/2" metal reducer bushing for the 1/2" metal conduit? Can I made this bushing rain tight?
3. If I use a metal box with 1/2" threaded connections, the 1/2" metal conduit is easy to connect. What would I use to connect the 3/4" PVC conduit?
4. I prefer to use a metal weatherproof box, but PVC weatherproof boxes are available with mixed 1/2" and 3/4" threaded connections, so the PVC box would eliminate the size adapter problem. If I used a PVC weatherproof box will this be NEC-compliant?
 
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You said: "... I would prefer to use a metal weatherproof box, but a PVC box would be OK if it's code compliant. ..." Yes, it can be metal. Ensure the metal is of the same material to that of the 1/2" conduit (don't connect dissimilar metals, ie.

QUESTIONS:
1)
You are correct, most exterior rated enclosures are threaded. You should use a 3/4" Then purchase from the same wholesaler a 3/4"-1/2" threaded reducer.
2) See answer above, yes above are raintight
3) I would avoid doing it that way. If you chose to do anyways, you need 1/2" by 1" close nipple, a 3/4"-1/2" threaded reducer, then a 3/4" threaded rigid coupling.....its no point in doing it that way, look clumsy too!
4) Yes, PVC is fine. Your 1/2" conduit needs a ground now though. Ensure you connect your green installed in the 1/2" conduit to the green/yellow in your UF-B. Wire it together well in this type of box as it is a dielectrical substance. Having done your, installation will be just fine.


Any other questions, just ask.
 
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Joined
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You said: "... I would prefer to use a metal weatherproof box, but a PVC box would be OK if it's code compliant. ..." Yes, it can be metal. Ensure the metal is of the same material to that of the 1/2" conduit (don't connect dissimilar metals, ie.

QUESTIONS:
1)
You are correct, most exterior rated enclosures are threaded. You should use a 3/4" Then purchase from the same wholesaler a 3/4"-1/2" threaded reducer.
2) See answer above, yes above are raintight
3) I would avoid doing it that way. If you chose to do anyways, you need 1/2" by 1" close nipple, a 3/4"-1/2" threaded reducer, then a 3/4" threaded rigid coupling.....its no point in doing it that way, look clumsy too!
4) Yes, PVC is fine. Your 1/2" conduit needs a ground now though. Ensure you connect your green installed in the 1/2" conduit to the green/yellow in your UF-B. Wire it together well in this type of box as it is a dielectrical substance. Having done your, installation will be just fine.


Any other questions, just ask.
Thanks. I think I am going to use a PVC box with 3/4" connections. On the top of the box I can use a 3/4-1/2 reducer for the 1/2" EMT conduit (TAYMAC boxes include reducers). On the bottom I just need a 3/4" PVC slip-thread adapter for the 3/4" PVC conduit. The THWN and UF-B ground wires will be connected in the box.

Just curious - in Canada do they refer to the connections as 3/4" and 1/2", or 19mm and 12.7mm? ;)
 

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