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Old 06-24-2007, 09:43 AM   #1
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Location: Levittown, Pa.
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Rigid Metal Straight Threads

I am planning to use rigid metal conduit under a length of concrete. The job requires me to cut out a 16 inch square hole in the concrete and dig down 12 inches to make a connection at a rigid metal elbow. I am concerned about the straight threads on the elbows,couplings and compression fittings that I will use. These straight threads do not allow for a tight connection to prevent water seepage to the inside of the conduit. How should I proceed to seal these fittings? I will use THWN conductors. Is sealing even necessary?
I have already been advised not to use sealant on the threads due to the chance of insulating the fittings. What about coating the connections after assembly?
I have already installed a run of Rigid PVC from a Gfci that is mounted on my front wall to another spot where it will connect to the Rigid metal conduit. This will end up in a receptical in the garden area.
So I am thinking that sealing the threads won't matter in my case as the rigid metal will lose grounding continuity at the Pvc connection and will only be grounded by the THWN green wire.
Should I be concerned and how to proceed on this?

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Old 06-24-2007, 11:05 AM   #2
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Rigid Metal Straight Threads

You will have water in that conduit no matter what you do. If you want, seal the joints after assembly. I guess it will slow water entering the conduit. Over time, water will condense inside the consuit, whether or not it leaks. That is why "W" rated conductors are required. (You have that covered with THWN)

John from Baltimore
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Old 06-24-2007, 11:42 AM   #3
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Rigid Metal Straight Threads

I'll be proceeding with confidence.
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