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Attic wiring with Nomex and EGC

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  • Attic wiring with Nomex and EGC

    Just put my rails up today and will be doing the wiring on Friday. I have a 7.5kW system using Enphase IQ7 microinverters on 2 strings. The system is on the opposite side of the house from the MSP. I bought a bunch of conduit but thought, why can't this be done in Romex? It would be a pain to get all the bends in my cramped attic, and it's a 240VAC circuit once it's in the attic. Some Googling showed some debate on this several years back, and the consensus was, yes this is acceptable. So here would be my plan:

    Enphase Q-cable -> #10 THWN in JB on attic -> through EMT into attic -> into JB -> to 10/2 Romex -> JB at end of attic -> #10 THWN -> Combiner through EMT

    Now, if you agree this is acceptable, how is the EGC run, since my plans spec #8? Can I run 10/2 and a separate #8 wire alongside it? Or should I just run 8/2? If I recall, it's against code to change wire sizes in a JB without a breaker....

    Thanks in advance!

  • #2
    I just had a thought, I could run #8 THWN to match the 8/2 Romex... It would be overkill, and cost maybe a hundred bucks more, but that would be to code.

    Then again, I would be attaching 12ga wire on the Q-cable to 8ga on the THWN.

    Comment


    • #3
      I was thinking of doing the same thing but had trouble finding #10 nm cable with #8 ground. I didn't think you could run a separate ground alongside nm? I opted for 3/4 FMC in the attic and transition to EMT outside on the wall to the panel. No inspection yet but AHJ said FMC was fine with ground wire (can't use FMC as ground) but unusual.

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      • #4
        Originally posted by peatmoss View Post
        I was thinking of doing the same thing but had trouble finding #10 nm cable with #8 ground. I didn't think you could run a separate ground alongside nm? I opted for 3/4 FMC in the attic and transition to EMT outside on the wall to the panel. No inspection yet but AHJ said FMC was fine with ground wire (can't use FMC as ground) but unusual.
        That's why I'm thinking the easiest route might be just 8/2 nomex. More expensive, but easier. I think it just means you need to run 8ga THWN.

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        • #5
          Somewhere, I thought I understood only DC power HAD to be in conduit. Your roof penetration has to be done in an approved manner, but once inside, it may only need to be labeled SOLAR SOURCE or some such.
          Do not cheap out for the enphase cables, or you will be tripping offline all the time from high voltage. That's the advantage of 500V DC strings, you make the long runs at high voltage and the inverter output can be very short.
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          • #6
            Originally posted by Mike90250
            Do not cheap out for the enphase cables, or you will be tripping offline
            all the time from high voltage. That's the advantage of 500V DC strings, you make the long runs
            at high voltage and the inverter output can be very short.
            AMEN to that. ALL of my lower voltage AC wiring has been or is being upgraded from the
            original so called ADEQUATE installation wire. Bruce Roe

            Comment


            • #7
              Originally posted by Mike90250 View Post
              Somewhere, I thought I understood only DC power HAD to be in conduit. Your roof penetration has to be done in an approved manner, but once inside, it may only need to be labeled SOLAR SOURCE or some such.
              Do not cheap out for the enphase cables, or you will be tripping offline all the time from high voltage. That's the advantage of 500V DC strings, you make the long runs at high voltage and the inverter output can be very short.
              I'm not sure I understand. The only Enphase cables I'm using is the Q cable that connects all the microinverters. It's a special chain of cable with the Enphase plugs on in. Once it goes in the JB under the panels, it transitions to THWN. I don't think there's any issue with using the Q cable in this manner, but please correct me if I'm wrong.

              One more question. Is a separate EGC required for each string of microinverters? I have two arrays that will meet in an attic JB, and share a conduit run to the combiner. Of course, the 240V lines will be separate, but can I wire nut the two EGC wires in the attic JB, and run one EGC the remainder? I don't see why not.

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              • #8
                Enphase Q cables are #12. From the attic I'll switch to #10. Are you saying that's not enough? I guess if you have a long string of Q cables then you will get voltage rise. I think the loss and voltage rise between #8 and #10 at 100 feet @ 240v/20 amps is negligible.

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                • #9
                  Originally posted by peatmoss View Post
                  Enphase Q cables are #12. From the attic I'll switch to #10. Are you saying that's not enough? I guess if you have a long string of Q cables then you will get voltage rise. I think the loss and voltage rise between #8 and #10 at 100 feet @ 240v/20 amps is negligible.
                  #10 should be fine, and agreed on the difference being negligible. I'm only planning on going #8 because I can then use 8/2 romex in the attic and use the ground in the romex, since my AHJ requires a #8 EGC.

                  I just need to figure out if I need a separate EGC for each circuit, or if I can combine them at the JB in the attic, and run only one to the combiner.

                  Comment


                  • #10
                    My understanding is that #8AWG is to ground the panels and the racking from any lightning strike. In my case I had Enphase wiring and DC wiring and I ran the #8 in conduit with the DC wiring. That #8 ran all the way to builing ground. The Enphase wiring after the J box was #10 Romex and the ground wire in that Romex was only terminated at the subpanel.

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                    • #11
                      Originally posted by Ampster View Post
                      My understanding is that #8AWG is to ground the panels and the racking from any lightning strike. In my case I had Enphase wiring and DC wiring and I ran the #8 in conduit with the DC wiring. That #8 ran all the way to builing ground. The Enphase wiring after the J box was #10 Romex and the ground wire in that Romex was only terminated at the subpanel.
                      Are you saying your EGC was only #10 at one point? I thought it had to be #8 from the racking all the way to the MSP?

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                      • #12
                        Originally posted by nsgoldberg View Post

                        Are you saying your EGC was only #10 at one point? I thought it had to be #8 from the racking all the way to the MSP?
                        No, I ran #8 solid to tie the racking and the panels together. That went into a J box with the DC cables and the #8 solid was crimped to #8 THHN stranded which ran all the way to the ground rod without interuption. The upgrade to #10 for the Enphase AC wires was simply to reduce voltage loss. It ran to a 20Amp breaker.

                        Comment


                        • #13
                          Originally posted by Ampster View Post

                          No, I ran #8 solid to tie the racking and the panels together. That went into a J box with the DC cables and the #8 solid was crimped to #8 THHN stranded which ran all the way to the ground rod without interuption. The upgrade to #10 for the Enphase AC wires was simply to reduce voltage loss. It ran to a 20Amp breaker.
                          Got it, thanks for clarifying.

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