NM Cable into Rooftop Jbox

[solarken]

I understand NM-B Cable is not permitted in wet or damp locations. The JB1.2 juncion box from EZ Solar is a fully flashed, surface-mounted box with a Nema-3R rating, and I install them under a solar module so they do not get direct splashing rain, only runoff down the shingled roof, within which the flashing is interleaved just like the shingles. In addition, sealant is used for secondary protection around the roof penetration area of the enclosure.

I am thinking of using the approach in the attached graphic for Microinverter AC wiring transition from Enphase Q-cable to NM-B for the run through the attic toward the combiner. All the NM-B I have has what appears to be THHN or THWN phase conductors within it, with PVC and nylon insulation, although it is not marked. The sheathing would be trimmed back to just beyond the NM connector, in the female PVC connector, andso would be well within the attic space, and not protruding into the Jbox. The Jbox in my opinion is just as dry as the attic, since it uses all the same principles to keep the space dry as is used to keep an attic dry. In fact, when you look at the ridge vent, and the box vents in the roof at this house, it sure looks like those are much more likely to allow a little water in than this Jbox that is flashed and caulked and sitting beneath a solar module.

I have read a few other posts that touch on the subject but not exactly with the application I am talking about here. Any thoughts about this approach? Any code references that I can use if I get any concern from the AHJ?

 

[hbiss]

That's no different than entering the back of an outdoor mounted panel with NM that we discussed many times here.

1) You can't strip NM and run the conductors by themselves even for that short length. They are not THHN because they are not marked.
2) How do you bond the metallic NM connector?

Use UF, don't use the connector and staple it close to where it enters the conduit. Run the sheath all the way into the box.

-Hal

 

[jaggedben]

This is one of those things people do all the time that is technically something that can be called out but in my experience rarely is and in my opinion mostly shouldn't be. I think NM entering a weatherproof box is fine. (I even see cable stripped and pulled through an LB and nipple up the wall from the crawl space to the panel, no one seems to care, and I struggle to understand what could go wrong.)

If it bothers you or you know an AHJ will call it out the solution is UF. Simple.

All those connectors aren't doing anything for you, code wise or practically. Just use a plastic strain relief connector straight into the back of the box. Or if you want to use a metal nipple and connector, put a grounding bushing in the box.

 

[Dennis Alwon]

NC has an amendment that allows nm in conduit outdoors but for no more than 6'.

NC Amendment

Exception: The raceway shall not be considered a wet location if:

(1) The section of raceway routed in a wet location above grade does not exceed 1.8 m(6 ft) in length;(

2) Any fittings or conduit bodies are water tight and listed for use in wet locations; and

(3) All termination points of the raceway are only open in any of the following: a. A dry location; b. Equipment suitable for outdoor use; orc. Equipment listed for use in a wet location.

 

[Dennis Alwon]

The installation is fine but extend the nm jacket into the JB.