DC Breaker sizing & Combiner boxes

HuckMeat
HuckMeat Registered Users Posts: 24 ✭
in PV Installers Forum - NEC, Wiring, Installation #1
I'm getting ready to order parts for installing a system, using strings of 3 REC-225 panels, Isc=8.2A

In my Combiner boxes, what size DC breaker do I need? I'm looking at the outback and midnite combiner boxes. I'm assuming this is sized based on Isc? (And NOT Imp).

Second, can I daisy chain combiner boxes, i.e. collect the panels on each polemount, then collect them at the center-most polemount in another combiner and use larger breakers there, to get everything onto my large cables back to the inverters/charge controllers?

Thanks in advance,
m
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #2
    Re: DC Breaker sizing & Combiner boxes

    From their spec. sheet (PDF):
    Max Series Fuse Rating (A) 15

    If you use the same large gauge cable to tie all combiner boxes together--then you should not need any fusing/breaker on the main cable going back to the charge controller.

    But, yes, you can cascade breaker boxes (you do this the other way with house wiring. 200 amp main breaker, 15-50+ amp fuses for each circuit).

    Personally, I don't like to install "extra" fuses/breakers. They are extra costs and points of failure if they are not needed.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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