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Thread: solar backfeeding onto a panel with a generator feed

  1. #1
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    solar backfeeding onto a panel with a generator feed

    I am installing 20 amps of Solar onto a 100 amp panel. I noticed the panel also has a 30 amp breaker wired into a generator.

    I am unclear about these rules if there are any. Does this generator limit the amount solar I can put onto this panel?

    thanks

  2. #2
    Join Date
    Jun 2012
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    NW Ohio
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    Well even if you did have rules to go by, the fact that the generator is on a 30 and your solar can supply a max of 20 that would be a total max of 50 amps that could be supplied to the panel if both were "on line" when the panel is rated for 100.

    The pitfall here is that I don't know how well a generators regulator handles seeing some foreign voltage being supplied by your solar system.

  3. #3
    Join Date
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    No ATS? Is there some kind of interlocking that prevents main and generator from being on at the same time? That interlock would also have to prevent solar and generator being on at the same time.

    In my opinion you don't have to count both generators for interconnection rules if they can't feed the same panel or feeder simultaneously. And you're going to need to make sure they can't.

  4. #4
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    As noted, if there is any chance that the inverter output is greater than the local load while the generator is connected you will risk damaging the generator, or at least causing the inverter to shut down. Or use a PV inverter that is specifically designed to work with a generator. That capability is usually only found in a hybrid (battery standalone plus line interactive) inverter system.

    Sent from my XT1585 using Tapatalk

  5. #5
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    I am not so sure the generator is even used, but it is there and the breaker is installed. The building is a farm stand with a number of refrigerators so I understand the need for a generator. Property has new owners whom I doubt even know they now own an old generator.

    That said, seems like I could just have the solar breaker and generator breaker adjacent to one another and put one of those toggle switches in that prevents both from being on at the same time.

  6. #6
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    Quote Originally Posted by bbartmasse r View Post
    I am not so sure the generator is even used, but it is there and the breaker is installed. The building is a farm stand with a number of refrigerators so I understand the need for a generator. Property has new owners whom I doubt even know they now own an old generator.

    That said, seems like I could just have the solar breaker and generator breaker adjacent to one another and put one of those toggle switches in that prevents both from being on at the same time.
    The usual way to configure a system like this is to have an ATS which prevents the generator and the grid to be connected to the loads at the same time (i.e., to each other) with the solar connected to the grid side of the ATS.

  7. #7
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    Quote Originally Posted by ggunn View Post
    The usual way to configure a system like this is to have an ATS which prevents the generator and the grid to be connected to the loads at the same time (i.e., to each other) with the solar connected to the grid side of the ATS.
    Therefore when the TS is a mechanical interlock between the main breaker and the generator breaker the only way to add PV would be to do a supply side tap.

  8. #8
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    Quote Originally Posted by GoldDigger View Post
    Therefore when the TS is a mechanical interlock between the main breaker and the generator breaker the only way to add PV would be to do a supply side tap.
    True, but I have seen them where the TS is between the main panel and a subpanel where the sub has the protected loads and the PV is connected in the main panel.

  9. #9
    Join Date
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    Two places where I see the strangest electrical stuff, agriculture and primary schools. You don't say if the is the service panel or not, so maybe it's a critical load sub-panel and there is an isolation contactor between it and the service that opens when the generator is running, "cough" probably not "cough." It's kind of up to you and the local inspector what you are going to have to do. You do not want the generator and the PV system on and connected together and the usual is to put the PV interconnection somewhere that would be isolated from the generator when it is running or to put a contactor in the PV circuit that opens if the generator is started.

    If the generator is something the owner or a handyman installed without a permit then the inspector might catch it and the owner would have to bring the whole thing up to code. Very messy.

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