Installing romex on Micro-inverter system

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System
System Posts: 2,511 admin
in PV Installers Forum - NEC, Wiring, Installation #1
First off, this is my second micro-inverter installation (in the same city). I am located in Southern California, and have to deal with an AHJ that is notorious for being difficult with Solar installations. I am using 38 sanyo 220 w mods, and 38 enphase m 210 240v.
This AHJ, like most, requires that any PV dc array conductors shall have a means of disconnect before entering a building. As we know, we have AC power out of the micro's and enphase has released papers, with nec code reference as support, justifying the use of the connectors as form of disconnect.
http://www.enphaseenergy.com/downloads/Enphase_White_Paper_AC_Connectors.pdf .

1. Has anyone experienced this issue, and what was the outcome?

The next issue is, the installation is for new construction, (resi), and the GC does not want the home runs to be visible. This creates loads of difficulties, due to the fact that their is very little room to run conduit in the ceilings and walls. The AHJ requires that all exterior raceway, (metal), be GRC. They also require that any rooftop conduit must extend 18" past the horizontal plane of the roof, inside the building, be GRC.

2. If I comply with these requirements, can I install a junction box 18" below the roof plane and use romex 10/3 for my branch circuit home run?

Because of the layout I have (4) branch circuits consisting of

38 mods 38 micros
6 micros 6x.88x1.25= 6.6 A
12 micros 12x.88x1.25= 13.2 A
11 micros 11x.88x1.25= 12.1 A
9 micros 9x.88x1.25=9.9 A

All branch circuits 2 pole 15 A circuits

Total ampacity of the system is 41.8 A
600 A main ( plenty of capacity )

Table 250.122 states that you may use a 10 awg egc ,for equipment or raceway with an ampacity not to exceed 60 A.

3. With this knowledge is possible for me to use the bare ground in the 10/3 romex for my egc?


Thanks for the Assistance
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #2
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    Re: Installing romex on Micro-inverter system

    1. Re: DC disco - Enphase is supposedly about 10% of all residential installs these days, so chances are they have encountered this before. Why not ask them? They may make you install a roof-top AC disco switch - but IMO (and Enphase's) is redundant as you pointed out. I've never heard of anyone installing a DC disco on an Enphase install - that'd require you to install 38 of them to comply!

    2. Re: GRC - Really, they make you use GRC instead of EMT? Talk about over kill. Anyway, yes, you should be able to run your conduit into a junction box under the roof and then run 10/3 romex.

    3. Re: ground run - depends on your AHJ. I have heard of some not even allowing romex and forced an installer to replace all romex with EMT. IMO - it's OK and saves a LOT of copper - your AHJ may say otherwise.

    BTW - you might consider center feeding your larger strings to reduce losses. Will make you use an extra pigtail and cap, but makes a bit of a difference with higher power panels and can reduce communications issues as well.

    http://www.enphaseenergy.com/downloads/EnphaseAppNote_Vdrop_Calculations.pdf

    What's the AHJ in this case out of curiosity?
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  • System2
    System2 Posts: 6,290 admin
    #3
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    Re: Installing romex on Micro-inverter system

    Sorry, the reason that I pointed out the AHJ requiring the DC disco; is that they have had difficulty differentiating between the two.I.E.... a rooftop mounted Solar Pv array with conductors entering the living space needs a disconnect, (mechanical), whether it is DC or AC conductors. Once they hear these specs they automatically think form of disconnect, be it dc or ac disco. I would rather leave the AHJ out for anonymity. If you want me to pm I can.
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