how to hook mc connectors in parallel

mikeo
mikeo Solar Expert Posts: 386 ✭✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
HI all. I am going to help upgrade a neighbors 12 volt off grid PV systems that supplies power to one of his outbuildings and the new 200 watt panels have MC connector pigtails. There will be five 11 amp (18.4 Vmp) parallel panels requiring a set of #2 AWG wires from the panels to the breaker box that supplies the charge controller. The distance is between 15 and 25 feet depending on wire routing. The panels will be mounted side by side in a single line and will cover 16 ft of roof. I understand the MC pigtails are 10 gauge and will need to be spliced under the panels into the 2 gauge wires. How is the best way to do this? There are no code inspectors to deal with but I want meet the intent of the code for safety considerations?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #2
    Re: how to hook mc connectors in parallel

    Given that each string needs a series fuse/breaker for over current protection... You will probably end up needing some combiner (home run everything back to one point, install combiner panel, run 2 awg from there back to the battery shed.

    Or, you will need a "combiner box" every 20'. :confused:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    #3
    Re: how to hook mc connectors in parallel

    yep get mc extension cables long enough to get to a combiner and cut them in half giving you a male and female end then run those to your combiner box. use a breaker for each panel then you will be all set
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #4
    Re: how to hook mc connectors in parallel
    Or, you will need a "combiner box" every 20'.
    I think I have talked him into spending a little more money for an Xantrex XW 60 MPPT controller, a bit of overkill but will simplify installation, as I can series 4 panels (instead of 5) for 76 volts nominal and set the controller for his 12 volt system. This way I can just buy 1 30 or 40 ft MC cable and cut it in half and run it to his current breaker box. I will need to change out his breaker for a 150 volt rated 20 amp DC breaker but that shouldn't be too difficult. No combiner box on the roof and no parallel string fuses needed. This will give him 44 amps to charge his 630 amp 12 volt battery bank which should be OK. This should cost him a little less money as he is trading 1 panel for a more expensive charge controller but saving money on not having to buy string fuses and combiner boxes and more expensive wiring. Plus making it much simpler for me.
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  • SolMan
    SolMan Registered Users Posts: 15 ✭
    #5
    Re: how to hook mc connectors in parallel

    Do you need overcurrent protection between XW60 and PV array also...?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #6
    Re: how to hook mc connectors in parallel

    It is not that th XW60 need over current protection--you will design the wiring to handle 156% of the panel's rated output short circuit current (if you follow the NEC rules for solar design).

    The fused/breakers required for solar arrays is to protect 1 string of solar panels (internal panel short or wiring short) from the power of two or more solar panel strings supplying their current into the short on one strings... Hence, the requirement for a Fuser/breaker per String when three or more stings are connected in parallel (i.e., fuse/breaker combiner box).

    Many people will put a disconnect/breaker somewhere in the panel input to the charge controller--but that is not a requirement. You can also just use a switch instead.

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