You won't find a specific discussion of this in the NEC. Maybe you'll understand once you know the story.
NEC requires equipment be suitable for its' location. For decades, it was assumed thea this meant compression fittings inwet locations. Then, one day about four years ago, some eager young engineer at UL had the bright idea of actually subjecting compression connectors to the "rain test." The connectors failed. OOPS!
UL responded by releasing a staten=ment that there were no fittings approved for wet locations. Manufacturers responded by re-designing theirs, and submitting them for testing. The new ones have, in theory, been available for two years now.
Just don't tell the local supply house that- they have "never heard of" the new style fittings, and continue to only stock the "unapproved" ones. I have yet to actually see one of the new ones- or have any inspector ask about them. My being in the "high desert" might have something to do with this lack of concern.
From an NEC standpoint, the new style fittings must be used in any wet location.
358.42 Couplings and Connectors. Couplings and connectors used with EMT shall be made up tight. Where buried in masonry or concrete, they shall be concretetight type. Where installed in wet locations, they shall be of the raintight type.
I have some of the new connectors, but some others have been on back-order long enough that I think my supplier forgot about it. I need to reorder. Per usual I see advertisments and fliers about things like this before the suppliers stock them.
The actual test for "wet location" stuff is to subject them to an artificial rain, with a pre-determined wind.
Typically, a trough will be set up about 7 ft. above the floor. This trough will have many, many 1/8" holes in the bottom, and a nail inserted into each hole. This causes the water to "drip" off. A large fan is used to "suck" the rain at a particular angle- if memory serves me, this is about 15 degrees off vertical. The item being tested is then subjected to this "rain" for a set period. "Passing" criteria vary somewhat by item, but the intent is to establish that there is no hazard created. Generally, some water entry is allowed.
Its more a listing thing rather than a code thing. NEC requires RT, but its listing that allowes it to be RT.
My understanding is that the old style compression fittings are still listed RT in Canada. Not sure if that will hold water...
The new style have been slowly hitting the supply houses here, and I have a stash of them in the van right now, I like 'em. Pricey, but nice. Ya gotta be nice putting them together, if you're too aggressive you'll find that O-ring stuck in the connector during your pull. Not a fun find.
Mark Heller "Well - I oughta....." -Jackie Gleason
Every time this comes up, I say this. I don't understand the issue here. The old EMT couplings are more raintight than threaded rigid couplings. Why is it a problem when the inside of the EMT is wet, but not when the inside of the rigid is wet? Don