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I recently installed some outdoor conduit, with weatherproof boxes and (the most expensive bits) raintight compression connectors. Because this is EMT conduit, set screw connectors were also available, but, obviously not wet rated.

I recently got to thinking, however, that THWN is, on its own, wet rated and the conduit merely serves as physical protection.

So, do I need to install raintight/weatherproof connectors for conduit when the wires within are already wet rated?

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    You do need fittings rated for a wet location. So yes the listed fittings are required. It may sound silly especially if you have dug up or pulled a low point in outside conduit and found it full of water. Any time I have a long outside run I add drain holes in the boxes. Listed fittings do reduce the amount of water that can enter the pipe. – Ed Beal Jun 7 '17 at 18:53
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Short answer: Wet locations only require corrosion resistant materials. But I would use compression connectors outdoors anyway.

From the National Electrical Code

358.10 Uses Permitted.

(A) Exposed and Concealed. The use of EMT shall be permitted for both exposed and concealed work.

(B) Corrosion Protection. Ferrous or nonferrous EMT, el-bows, couplings, and fittings shall be permitted to be in-stalled in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by cor-rosion protection and approved as suitable for the condition.

(C) Wet Locations. All supports, bolts, straps, screws, and so forth shall be of corrosion-resistant materials or protected against corrosion by corrosion-resistant materials.

Good luck!

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Only outdoor electrical conduit should be used outdoors.

Water-resistant wire just resists water. It is not meant to be immersed in water. If your conduit or boxes fill up with water, it will short out and/or you will get leaks.

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  • 1) It's EMT which can be installed outdoors. 2) The boxes are outdoor, weatherproof boxes. 3) Obviously if it gets filled it will short. That's often why there is a drain hole provision. – Hari Ganti Mar 31 '17 at 20:27
  • You've never had underground conduit... Even PVC is full of water 99% of the time. – Tyson Mar 31 '17 at 20:29
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    @TylerDurden less about the conduit than using the conduit as the grounding path. But agreed; bad news. In any case trying to keep outdoor conduit from filling with water is a lost cause, you win that war with the water-rated wire. – Harper - Reinstate Monica Mar 31 '17 at 21:24
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    @TylerDurden Out of curiosity, what exactly are you referring to when you say "standard conduit"? I'm actually unsure if you mean Sch 40 PCV, EMT, RMC, etc. – Hari Ganti Mar 31 '17 at 21:57
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    Also, concerning the outdoor ratedness of EMT, NEC 358.10(A)(2): [The use of EMT shall be permitted for both exposed and concealed work for the following:] In dry, damp, or wet locations. – Hari Ganti Mar 31 '17 at 22:00

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