PV connection to feeder?

Brent
Brent Solar Expert Posts: 64 ✭✭✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
Hope someone might be able to clarify this for me.

I would like to add two SunnyBoy inverter AC outputs to a 100A load center [100A bus & 100A brkr] in a garage [use as an AC combiner as well as supply existing loads]. Each inverter will require a 20 A breaker in the load center. The load center currently has 3 - 20A breakers. The bus rating of the main service panel will handle the PV source current ok. I will need to label the garage 100A breaker in the service panel as a PV circuit.

If I label the load center 100A panel to specify that any additional loads are not to be added can I use it in this manner?

I could find no specific Code reference in the 2010 California Electrical Code handbook addressing an AC combiner having branch ckts. If anyone knows of the specific article allowing or disallowing this I would be grateful.

The alternative would be to have a dedicated AC combiner for the inverters and a dedicated run to the main service panel but this is not very practical in this application.

Thanks,

Brent
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: PV connection to feeder?
    Brent wrote: »
    I could find no specific Code reference in the 2010 California Electrical Code handbook addressing an AC combiner having branch ckts. If anyone knows of the specific article allowing or disallowing this I would be grateful.
    The 120% rule specifically states that the total of all of the source breakers (in this case main plus PV) cannot exceed 120% of the busbar current rating of the panel.
    It does not mention loads at all. But the reason for the 120% rule in the first place is to prevent load current from overloading the bus. No loads, or very limited loads, and that is not a problem. Unfortunately the NEC does not recognize an exception to the 120% rule if you limit loads.
    Now if you put a 75A main breaker in or find a 100A panel with busbars rated at 125A you will be OK.
    If there are no loads at all, it is a combiner rather than a subpanel supplying loads.
    A similar argument has been applied to the ampacity of the wires from a line-side-tap to a subpanel or combiner box. With mixed results.
    SMA SB 3000, old BP panels.
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  • Brent
    Brent Solar Expert Posts: 64 ✭✭✭✭
    #3
    Re: PV connection to feeder?

    Thanks for the input. I forgot to mention that I planned to limit the main breaker on the load center to 60 Amps. In reference to 690.64(B)(2) the sum of all breakers supplying power to the panel equals 60+20+20=100A.

    Brent
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #4
    Re: PV connection to feeder?
    Brent wrote: »
    Thanks for the input. I forgot to mention that I planned to limit the main breaker on the load center to 60 Amps. In reference to 690.64(B)(2) the sum of all breakers supplying power to the panel equals 60+20+20=100A.

    Brent

    You actually can go to 80 amps on the panel to meet the 120% rule for the panel buss bar. 80+20+20= 120 amps . 60 amps keeps you way below.
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