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Thread: Some art 690 advice needed please

  1. #1
    Join Date
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    Some art 690 advice needed please

    It's all updated in the '17 , and to be truthful i didn't have the best handle on it to begin with

    So here's the scenario, bare with me....

    Older home, 100A service drop to two meters, house & offpeak hot H20, all older se cable into two mains, 100A house, 30A hot H20

    Panel has been upgraded (Siemens 30 cir cu buss w/main)

    Off peak hot h20 is gone , small two banger 30A disco remains, meter still exists and is sealed

    Solar guy wants to install >(21) LG panels rated 330 watts each / approx 6.93 KW ,with Solaredge inverter SE6000H-US

    Claims the panel can't handle it

    But the poco will allow a 'line tap' the unused hot h20 as a (rewired to) net meter

    Where do i start with this? Does the service need to bump up to a 150? 200?

    Thx in advance

    ~RJ~

  2. #2
    Join Date
    May 2011
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    4,640
    Well, start in Article 705, not 690... Specifically 705.12.

    The service does not need to bump up because it's well above the 35A output required by the inverter.

    If the new Siemens panel really has 100A busbars and not 125A busbars then the solar guy is most likely correct that the panel can't code compliantly handle the backfeed. If by some chance the load breakers on both busbars both add up to 65A or less then it would be okay, but that's not likely. I express a little skepticism about the busbar being 100A if it is a relatively new upgrade, since I don't see too many new 100A rated busbars anymore rather than 125A, but it's certainly possible. If the busbars are actually 125A then your services are not needed.

    If the utility indeed allows the second meter to be used for the solar and the customer understands the metering regime and gives that the go ahead (I only say all that because it wouldn't be allowed around here), then that service disconnect presumably needs to be upgraded to a 60A disconnect with 35A fuses to allow the inverter output. (Or downsize the system to a 5000W inverter, which would produce a bit less energy but might cost less than whatever you charge to replace the disconnect. Oh wait, you probably don't want to tell them that, huh? )

  3. #3
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    Thanks Jag...

    So i'm finally in the right article & 705.12A seems a lot less restrictive than 705.12B to me.

    Seems I could park a nema3r disco next to & use the old off peak hot H2O meter as a net meter w/o much worry

    POCO is cool with it here, they've a 'net meter' contingent that's a lotta help.

    They call 705.12A a 'line tap' , yet I feel i'm missing something in that B needs some calc done against the service (or at least panel) size, where B forgoes any of it?


    Unfuzz me , but by my reading it would appear that if the panel was a 150A on 100A serv ent wiring , it'd fly for B??

    ~S~

  4. #4
    Join Date
    May 2011
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    I think it is implied that the total (continuous) output connected under A and B can't exceed the service rating. But that isn't explicit.

    Utility import and solar export currents can't add together on the service conductors, so they only have to be sized for the larger. Residential solar systems don't usually trigger an upgrade to the service conductors, unless there's some ancillary reason (such as no longer meeting a 230.71 minimum, or a utility's non-NEC rule). I.e. one can usually just replace a panelboard. In your case only the service entrance conductors for the 2nd meter might be at issue.

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