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Situation: outside service panel with a meter and plenty of breaker spaces, mounted on siding surface. The panel does not appear to be moisture-tight, there are no gaskets on the covers and entry for the existing subpanel feeder is from rear via a standard SER cable coupling (through the siding and back KO). enter image description here Is this considered a "wet" location by the code? (I think it should).

What cable type should I use to connect a new subpanel that will be directly behind it, connected via a nipple (separated only by the siding thickness, say 3/4")? THHN or THNW (or other wet-location certified equivalent)?

If I wanted to add an outlet with a weather-proof in-use cover and box - what cable can I use for it? (probably "wet" only).

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NEMA 3R (outdoor) does not normally have gaskets, it just has a drip pattern that channels water away from live components, and wire is required that is wet location rated. The labeling on the reverse of the cover of the cabinet should indicate the NEMA rating.

The term "Cable" normally describes a multiconductor assembly, which isn't really appropriate for a new wet location in-use receptacle. There are limitations included in the installation documents that tell you where penetrations are allowed in the cabinet that keep the 3R rating. Probably easiest to use a short piece of 1/2" PVC to a weathertight junction box and use THWN conductors. The W is wet location. All THHN conductors I have ever seen are dual rated THHN/THWN, but keep your eyes open, there might be an exception.

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  • The existing back KO entrance is custom made and it's not a wethertight. It have passed inspection when this new service was installed thought it's questionable.
    – Michal
    May 23, 2021 at 15:49
  • Indeed, the label says "TYPE 3R ENCLOSURE RAIN_PROOF".
    – Michal
    May 23, 2021 at 16:04
  • I think the raceways that ourt in weather-unprotected areas are considered "wet" location but the insides of pannels or junction boxes that are NEMA 3R are not "wet" as they are not raceways. Also the rear entry to this pannel may be considered "dry" as it does not leave the weather protected "inside".
    – Michal
    May 26, 2021 at 3:53

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