Transitioning from 1/2" EMT to 3/4" RNMC

2516 Views 8 Replies 6 Participants Last post by qbert, Apr 4, 2009

kornbln

Discussion Starter · Apr 2, 2009

I have 1/2" EMT attached to the side of a house which comes down the wall into a weatherproof box with a receptacle. A 3/4" RNMC comes up from the ground next to the house, up the wall and into the same box using a male terminal adapter. The problem is whoever installed this didn't do it right. The weatherproox box has 3/4" hubs. The 1/2" EMT has a connecter on it inserted into the box. Just inserted. Not threaded in because it isn't the right size. What should I do to correct this? I was looking at a rigid reducing bushing which will work with an EMT fitting, but apparently they are only for use in dry locations. Should I cut the terminal adapter off the RNMC and glue on a reducer? I was looking at various reducing fittings in the Carlon catalog but I'm not quite sure I understand how they work. If I need multiple pieces, etc.

Also, I want to make sure I am correcting some other portions of this the right way. The original installation was done with die-cast EMT set screw couplings and box fittings. I've replaced all of those with raintight fittings. How does one make RNMC entering a weatherproof box raintight? Do I glue it in or use some sort of thread sealant or anything?

Hope this makes sense, otherwise I can draw a sketch.

Thanks

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rgsgww

· #2 · Apr 2, 2009

How far is the emt extending from the wall? Can you get a picture of it?

Is it possible to notch around the emt and install the proper connectors to install a box flush on the wall?

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kornbln

Discussion Starter · #3 · Apr 2, 2009

rgsgww said:
How far is the emt extending from the wall? Can you get a picture of it?

Is it possible to notch around the emt and install the proper connectors to install a box flush on the wall?

Not sure I understand what you are suggesting. Can't take a photo right now but here is a sketch...

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InPhase277

· #4 · Apr 2, 2009

Use a reducing fitting for galvanized plumbing pipe. No, it isn't UL listed for that particular purpose, but it is surely capable of standing up to a wet environment.

As to sealing a weatherproof box, you pipe is coming from the bottom, so there really isn't a need to seal the treads. Otherwise, the connection between the threads is still pretty tight. I have never had a problem with water entering a box in that manner.

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kornbln

Discussion Starter · #5 · Apr 3, 2009

InPhase277 said:
Use a reducing fitting for galvanized plumbing pipe. No, it isn't UL listed for that particular purpose, but it is surely capable of standing up to a wet environment.

That's not a bad idea but there has to be a code-compliant solution without the use of a plumbing part. I thought the threads are slightly different on plumbing vs electrical fittings. I wonder if the rigid reducer bushing I was looking at in the hardware store has a different listing than the one I linked to. The one I saw was actually steel, not die-cast zinc.

I thought about using a weatherproof box extension ring with 1/2" hubs but I'd like to avoid that...

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micromind

· #6 · Apr 3, 2009

An explosion-proof bushing would be watertight, but you'd have to go to an electrical wholesaler to get one. And they'd likely have to order it for you.

Rob

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kornbln

Discussion Starter · #7 · Apr 3, 2009

What about a reducer on the RNMC side? How do those work?

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goose134

· #8 · Apr 4, 2009

This easy, though it requires a number of parts. First use a reducing bushing in the 3/4 hole.Then for the sealing part, use a sealing locknut ( a steel locknut with a built in gasket) on a threaded close nipple. Screw on a GRC coupling. Then to the female end of the rigid coupling, screw in a threaded PVC fitting.

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qbert

· #9 · Apr 4, 2009

3/4 myers hub and 1/2 x3/4 threaded bushing and 1/2 emt compression fitting

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