Two breakers on one wire.

rgk1
rgk1 Solar Expert Posts: 135 ✭✭✭
in Off Grid Solar & Battery Systems #1
My old system was very simple and only had a breaker on the solar input for convenience and is located inside the power shed.  However, I now have 4 panels with two series and then parallel via a combiner box with breakers that is located outside the power shed.  I didn't really think anything about it till now.  Is it OK to have the solar positive going into the breakers in the combiner box and then the combined output of that going thru another breaker on the "shutoff" box inside the building? Breakers in series? 
4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    If I'm understanding correctly, it's OK to have breakers in series as long as the breaker with the lowest current threshold is sized to protect the smallest conductor within the series circuit, in other words if each breaker in the combiner is rated below the current carrying capacity  the feeders to the controller, then the convenience breaker could be oversized because it serves as a disconnect, not as an over current protection device.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #3
    Thanks mcgivor! That is the way it is.  Solar panels to combiner breaker sized for 10awg (think I used a 15a). Combiner output to convenience breaker is 4awg and has 20a breaker - then on to controller. Just didn't want to end up with effective 35a worth of breaker before a trip.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #4
    May have given some  potentially  misleading information, if the combined current of the parrallel circuits exceeds the current carrying capacity of the feeders to the controller, then it would be required to provide overcurrent protection for the feeders, so the convenience disconnect, breaker, would need to be sized at no more than 125%, than that of the conductors rated current carrying capacity..
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #5
    You have lost me a bit.  Two positives wires from panels - each 10awg and string VOC 91.4V / 9.15A each going into its own 15a breaker in the combiner (15A protects the 10awg?).  Combined output out of combiner box is 4awg and VOC 91.4V / 18.3A - in theory.  This 4awg goes to the convenience disconnect (20A breaker protects the 4 gauge?) then to controller with 4 gauge wire as well. 
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited October 2020 #6
    Just wanted to be clear that I understood exactly what the configuration was as it's easy to misinterpret something..
    What you described is fine if the current is the rated IMP value from the panels,  actual current will be less in most conditions. Should the 20A breaker trip , it could be replaced with a larger value but not exceeding the maximum for 4 AWG.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #7
    Correct, the values used are the highest listed on the panels. Thanks again for the help!

    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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