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How to transition between panel groups on residential rooftop install

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  • How to transition between panel groups on residential rooftop install

    house with panels edit.jpg

    I am self-installing a 4K grid-tied PV system in California. I have 3 groups of panels, wired into 1 string. How do I get cables from one group of panels to the next? Do I run conduit between them? One source says "PV and USE-2 wires cannot be run through conduit." If not conduit, how do I keep those wires off the roof surface? If I run conduit, do I use PV wire, or transition to something else in the conduit, then back to PV on the other side?

  • #2
    Use EMT conduit. I believe what your source means is that USE or PV wire cannot be run indoors because it is not smoke rated, but outdoors is just fine. Be sure and ground the EMT conduit with bond bushings.
    BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed


    • #3
      Thank you. This is exactly the explanation I needed. Yes, my source mentions that you can't run PV in conduit because it's not flame resistant, and now with your explanation I get that what he means is, you can run it indoors. So it's PV wire in EMT on the roof between panel groups for the win!


      • #4
        i have similar situation and had a few additional questions that I have been pondering.

        - What size conduit would fit the 2 PV cables?
        - Would you also run a grounding wire in the conduit to ground the rails?
        - I presume you have to do the run the cable through without the MC4 connector? (I was hoping to not have to buy a mc4 crimping cable).
        - Since this is just to protect from the UV, is any cap at either end required?


        • #5
          I use 3/4" EMT. Yes, I run the ground wire through the conduit. And you're going to need a MC4 crimping tool (about $20) because you're going to need to make some extension cables, and they're significantly less expensive to make than they are to buy. And when you make them, you can make them whatever length you need. And yes, then you can pull the wire through conduit before you attach the MC4s. I don't have a cap at the ends of my EMT. Some people run the conduit to a box, then run the cable out a cable gland. Too much trouble IMO.


          • #6
            Thanks for the quick response. Sounds like a good plan. I thought the mc4 crimpers were significantly more so I'll definitely do some more research.