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Thread: Micro-Inverters in the Attic

  1. #1
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    Burleson, Texas
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    Micro-Inverters in the Attic

    Hi all,

    I am looking to install a PV system on my roof using micro-inverters, but my situation wont allow for these inverters to be mounted on the roof, so i want to install them in the attic below the array and join them together there. Im aware that the DC cabling inside the attic is required to be in conduit or enclosure before it reaches the inverters, but once its converted to AC is Romex ok to join the inverter outputs together?
    is there any other rules im missing?

  2. #2
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    Dec 2012
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    Quote Originally Posted by MikeNZ View Post
    Hi all,

    I am looking to install a PV system on my roof using micro-inverters, but my situation wont allow for these inverters to be mounted on the roof, so i want to install them in the attic below the array and join them together there. Im aware that the DC cabling inside the attic is required to be in conduit or enclosure before it reaches the inverters, but once its converted to AC is Romex ok to join the inverter outputs together?
    is there any other rules im missing?
    You are potentially overlooking the consequences of Rapid Shutdown requirements in recent Code cycles. One advantage of micro-inverters is that the uncontrolled DC from the panels does not travel outside the array, avoiding some of the rapid shutdown requirements. Bringing the DC inside the attic may trigger those requirements and shutdown at the microinverter itself would not be sufficient.

  3. #3
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    Quote Originally Posted by MikeNZ View Post
    Hi all,

    I am looking to install a PV system on my roof using micro-inverters, but my situation wont allow for these inverters to be mounted on the roof, so i want to install them in the attic below the array and join them together there. Im aware that the DC cabling inside the attic is required to be in conduit or enclosure before it reaches the inverters, but once its converted to AC is Romex ok to join the inverter outputs together?
    is there any other rules im missing?
    Microinverters typically mount up under the module backsheet inside the frame. I don't see how you could mount modules but not modules with micros. Mounting microinverters in the attic would be, IMO, a wiring nightmare. You'd have to either have a roof penetration under every module or home runs between every module and its inverter. It's not something I would ever consider.

    Some AHJ's I deal with allow microinverter interconnections with Romex but some also require a #8 ground wire.

  4. #4
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    Quote Originally Posted by ggunn View Post
    Microinverters typically mount up under the module backsheet inside the frame. I don't see how you could mount modules but not modules with micros. Mounting microinverters in the attic would be, IMO, a wiring nightmare. You'd have to either have a roof penetration under every module or home runs between every module and its inverter. It's not something I would ever consider.

    Some AHJ's I deal with allow microinverter interconnections with Romex but some also require a #8 ground wire.
    I've seen some resi roof mounting systems that won't allow MLPE boxes under the modules. They are zero clearance systems that attach the modules flat to the roof. I don't see them often because with no back of module airflow it really heats up the modules and reduces the output but they are out there. RSS will probably kill them off.

    Since you will have a lot of roof penetrations OP make sure your sealing technique is 100%. Better yet, use a string inverter.

  5. #5
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    May 2011
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    Just use a racking system that allows them on the roof.

    Rapid shutdown doesn't apply if DC is only one module worth.

  6. #6
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    Quote Originally Posted by jaggedben View Post

    Rapid shutdown doesn't apply if DC is only one module worth.
    How so? Plenty of DC modules have Voc > 30V.

  7. #7
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    Micro Inverters should be listed for 30-40c ambient, not 50-60c in attic space, or garage space.

    Same reason smoke detectors won't work, and not required in attics or garages.
    Roger Ramjet NoFixNoPay

  8. #8
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    Quote Originally Posted by ggunn View Post
    How so? Plenty of DC modules have Voc > 30V.
    I guess if one extended the DC conductors beyond the length of the module leads then 2017 requirements could be triggered. Otherwise I see it as quite unlikely they'll be outside the array boundary. Perhaps my comment was unwarranted though; yes it could be an issue if one installed them just so.

    Quote Originally Posted by ramsy View Post
    Micro Inverters should be listed for 30-40c ambient, not 50-60c in attic space, or garage space.

    Same reason smoke detectors won't work, and not required in attics or garages.
    Roof surfaces get really hot too. The Enphase IQ7 has a max temp rating of 65C. There are a bunch of reasons I think it's a bad idea but that's not high on the list.

  9. #9
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    Quote Originally Posted by pv_n00b View Post
    Since you will have a lot of roof penetrations OP make sure your sealing technique is 100%.
    It's not IF a roof penetration will leak, it's WHEN. Punching that many holes in the roof is just BEGGING for roof leaks that will be impossible to get to, what with being underneath the apparently zero-clearance mounted panels.

    You want to put as few holes as possible in a roof, and do it absolutely correctly when you do. Call a roofer for roof penetrations, and let someone else take the liability.

    Find a different racking system that allows the inverters to be mounted behind the panels, and make the roof penetration somewhere that's NOT directly under the array, so it can be serviced later.


    SceneryDriver

  10. #10
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    Quote Originally Posted by SceneryDriver View Post
    Find a different racking system that allows the inverters to be mounted behind the panels, and make the roof penetration somewhere that's NOT directly under the array, so it can be serviced later.
    We frequently put Soladeck boxes under the array for aesthetic reasons, but it's just one penetration per array that's not into a rafter and getting to it is pretty easy.

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