100 amp service, and 30 amp GVFX selling power?

verdigo
verdigo Solar Expert Posts: 428 ✭✭
in Grid Tie and Grid Interactive Systems #1
It just occurred to me that my antique 100 amp breaker box might not be legal to support up to 30 additional amps from my GVFX3648 inverter. It wouldn't break my heart to replace it but if its okay I wouldn't bother as the pole to house cables would have to be replaced as well.

The electrician and inspector are coming by today to okay my plans or not.

Thanks

Dennis
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: 100 amp service, and 30 amp GVFX selling power?

    This is an interesting point because the answer is "no" or "yes". :D

    The 100 Amp service is at 240 VAC whereas the GVFX output is 30 Amps @ 120 VAC.
    If you put a transformer on the inverter and up the Voltage to 240 the available current halves to 15 Amps which is within the 20% NEC rule.
    But if you don't then you're hitting one bus bar with 30 Amps which is over it.

    Then there's the question as to whether or not an inspector would understand it either way. :roll:
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  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    #3
    Re: 100 amp service, and 30 amp GVFX selling power?
    Cariboocoot wrote: »
    Then there's the question as to whether or not an inspector would understand it either way. :roll:

    The inspector just left. I had to tell him what a charge controller does. He is going to get a utility guy to come out with him at some later date. He was a real nice guy though. I was having a tough time explaining the by-directional hot. That it was to power the internal battery charger, and that it sends power out to the grid. Told him it was magic and "hey look, it has a UL sticker too".
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  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    #4
    Re: 100 amp service, and 30 amp GVFX selling power?
    verdigo wrote: »
    The inspector just left. I had to tell him what a charge controller does. He is going to get a utility guy to come out with him at some later date. He was a real nice guy though. I was having a tough time explaining the by-directional hot. That it was to power the internal battery charger, and that it sends power out to the grid. Told him it was magic and "hey look, it has a UL sticker too".

    Oh man. Don't even get me started about inspectors not understanding the basics of a solar installation. Strict grid tie- maybe -but once you add in battery back up, charge controllers and basically anything DC forget it. The grounding issues are also a whole 'nother can of worms that they're likely to not understand...:roll:

    Good luck!
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #5
    Re: 100 amp service, and 30 amp GVFX selling power?
    verdigo wrote: »
    It just occurred to me that my antique 100 amp breaker box might not be legal to support up to 30 additional amps from my GVFX3648 inverter. It wouldn't break my heart to replace it but if its okay I wouldn't bother as the pole to house cables would have to be replaced as well.
    0. With a GVX output of 30A, the NEC requires you to size the backfeed breaker at 30 x 1.25 (for an inverter with batteries) or 30 x 1.25 x 1.25 (for a pure grid tie inverter).
    The only ways that you would be OK with the existing box would be:
    1. Use a transformer or autotransformer to spread the backfeed between L1 and L2.
    2. Put a smaller breaker in place of the existing 100A main.
    3. Hope that the bus in your 100A panel is actually rated at 125A (not unlikely, but hard to document for an old panel.)
    SMA SB 3000, old BP panels.
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  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    #6
    Re: 100 amp service, and 30 amp GVFX selling power?
    inetdog wrote: »
    0. With a GVX output of 30A, the NEC requires you to size the backfeed breaker at 30 x 1.25 (for an inverter with batteries) or 30 x 1.25 x 1.25 (for a pure grid tie inverter).
    The only ways that you would be OK with the existing box would be:
    1. Use a transformer or autotransformer to spread the backfeed between L1 and L2.
    2. Put a smaller breaker in place of the existing 100A main.
    3. Hope that the bus in your 100A panel is actually rated at 125A (not unlikely, but hard to document for an old panel.)

    I am already there on the auto transformer. Putting a smaller breaker in place of the 100 amp main I don't get?
    4
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #7
    Re: 100 amp service, and 30 amp GVFX selling power?
    verdigo wrote: »
    I am already there on the auto transformer. Putting a smaller breaker in place of the 100 amp main I don't get?
    4

    The NEC allows you to source upto 120% of the panel buss bar rating for a 2 sources of power. The 100 amp main suggests that the largest back feed would be a dual 20 amp 240V L1/L2 breaker. To do a 30 amp 120V back feed would require down sizing the main input breaker to less than 91 amps to stay inside the letter of the code..
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  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    #8
    Re: 100 amp service, and 30 amp GVFX selling power?

    Gotcha. hadn't thought of that.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #9
    Re: 100 amp service, and 30 amp GVFX selling power?
    mtdoc wrote: »
    Oh man. Don't even get me started about inspectors not understanding the basics of a solar installation.
    I had an inspector come out to look at a 300kW rooftop system once with me (design engineer) and the project manager. When we got to the roof the inspector looked over at our bank of 42 SMA SB7000's and said, "Those are microinverters, right?" The PM and I just looked at each other.
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