Will I have enough Amps?

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  • Joe J
    Joe J Solar Expert Posts: 49 ✭✭
    #32
    Re: Will I have enough Amps?

    I was rereading most of the posts. The item I'm a little fuzzy on is the ISC (short-circuit current) and being able not to use a fuse. I'm going to use the 3 panels in series with 2 in parallel. I understand if you use 3 in parallel you would than have to fuse each string. Does the panel become the fuse? Meaning the panel will short before the wire does? If you have 3 panels in series does it not "see" or harm the one panel next to it because of potential being balanced? Also, by not running a fuse in this situation is this up to code? Fire safety? So, In laymen terms how does this work?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #33
    Re: Will I have enough Amps?

    Joe;

    When you have only two parallel strings (one or more) of PV's with identical Isc rating there is no danger of overheating the wire should one of the panel strings become even completely shorted as the other panel string can not under any circumstances produce more than its Isc rating (which the other is capable of handling). So as far as the producing string is concerned it is just pushing current to a short circuit which it can do forever.

    If you add even one more parallel connection to the mix the ration changes: the two good strings can now push 2X the Isc rating to the short, causing overheating of conductors and possible fire.

    Series connections do not affect current (but do affect Voltage and increase the arc fault risk).

    Now there is the possibility that the short may occur in the charge controller and the panels will push their Isc to that, which will usually just fry some fragile internal component in a fuse-like manner. This is very unusual and not much of a hazard. Inspectors may disagree about that and require some circuit protection between whatever array you have and the controller. Some may demand a shut-off no matter what.
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  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    #34
    Re: Will I have enough Amps?

    SquareD (Schneider Electric) QO-series LoadCenter boxes and breakers make a suitable, legal, and economical solar combiner box for small arrays running at less than 60 volts. The QO, QOB and QOU are rated to 50 amps at 48 Vdc 1 and 2 pole, 10-70 amp and 3 pole 10-60 amp. The QOU is UL listed for 60 Vdc per pole 80-100 amps, 1 and 2 pole, and 70-100 amps, 3 pole.

    You can go to Menards and get a 5 place QO box for about 20 bucks and the single pole breakers are 6 bucks apiece.
    --
    Chris
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  • Joe J
    Joe J Solar Expert Posts: 49 ✭✭
    #35
    Re: Will I have enough Amps?

    Will post new topic
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