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eventual question: for a sealed PVC conduit external to house, does that qualify as a wet or damp location preventing use of non metallic (NM or NM-B) indoor type wire? And does underground feeder (UF) type of wire need to be used within that conduit?

scenario is regarding schedule 40 PVC gray electrical conduit {outdoor rated} run on outside of house from 1st floor (load center access) to access attic above 2nd floor. And this is along side same type gray PVC conduit of the same length that encloses single phase 2-wire 240 volt feeder from pole to house leading down into the electric meter socket/box (typical U.S. setup). Both conduits are the same length about 14 feet on the outside of house. Only practical means of getting new electrical run is along outside of house and penetrate attic wall, everything above concrete foundation and above grade by at least 3 feet.

  • a) difference between "raceway" and "conduit". does this definition matter? This is regarding circular conduit, schedule 40 NEMA TC2 the type used to connect to meter sockets. I think it's PVC, the gray electrical circular conduit definitely schedule 40 or above.
  • b) using the types of outdoor conduit bodies available today (21st century) they are quite durable and water tight, they come with gaskets on their covers. With solvent welding the plastic pipe and such good conduit bodies available does this run of conduit still classify as a wet/damp location such that the typical NM-B THHN indoor romex single run cannot be run within a 2" or 3" piece of conduit, per NEC interpretation?
  • c) does drainage matter for what has been described?
  • d) does a dual rating of THWN on the romex allow it? I don't remember at the moment if the typical romex 14/2 or 12/3 wire is also THWN. What about other wire ratings such as XHH or XHHW?

NEC-2017 sections:

  • 310.B and 310.C page 70-145
  • 334.10 and 334.15 page 70-191
  • Why run cable in conduit? Miserable, stiff pull. – Harper Apr 4 '18 at 23:38
  • Only practical means of getting new electrical run is along outside of house and penetrate attic wall. Not running UF-B or similar outdoor cable up outside of house for ghetto look... only one run to AC air handler in attic within conduit is a clean simple look. – ron Apr 5 '18 at 1:40
  • too many "pros" willing to pass off the easiest way to do it and say that's how it has to be done because of code – ron Apr 5 '18 at 1:42
  • Sorry I mean why run cable in conduit? Why not run individual wires... virtually all are wet rated. Everything I do is in conduit, it's easy mode with wires. – Harper Apr 5 '18 at 2:16
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Yes, that conduit counts as a wet location

All raceways in wet locations are considered to be wet on the inside as per NEC 300.9:

300.9 Raceways in Wet Locations Abovegrade. Where raceways are installed in wet locations abovegrade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations abovegrade shall comply with 310.10(C).

This means that the answers to your questions are, in turn:

a) Conduit is a kind of raceway (see the definition of "conduit" in Art. 100) (there are also surface raceways)

b) You will still get condensation in the raceways even if the joints are sealed by solvent welding. So, you will need to use wet-location-rated wire or cable (not NM!) in the conduit.

c) Drainage does matter -- 314.15 states that boxes and conduit bodies in wet locations must be arranged so that water is not trapped. It also provides that you can field-fit drainage openings no larger than 1/4" to boxes or conduit bodies in damp or wet locations, or use listed drainage fittings in knockouts for that matter. Take advantage of this, as drainage is your friend, and so is pressure moderation!

d) NM has a paper separator layer in it that makes it unsuitable for wet locations, period, even if the inner conductors were dual-rated. In general, stuffing cable down conduit is more annoying than it's worth, so you're better off getting dual-rated (THHN/THWN or XHHW-2) wires of the appropriate gauge and using those instead of a cable.

  • do you or anyone know drainage is handled for conduit fitted to the meter socket boxes for the incoming service from the pole?? I have a milbank 200 amp box, 2" conduit enters top and exits bottom, goes about a foot to a LB conduit body to enter through house- above foundation but below ceiling in basement with 90° going to load center. thanks. – ron Apr 5 '18 at 1:36
  • @ron -- I'd put a slight up pitch on the conduit going into the house, and then use a drill bit to put a 1/4inch hole carefully into the bottom front cover of the LB while the cover is off. (I'd rather put it in the bottom, but you'd have to pull the wires out of the LB to do that without risking insulation damage.) – ThreePhaseEel Apr 5 '18 at 1:57

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