MC4 Parallel Wiring & Voltage Drop

zulu Registered Users Posts: 1
For an RV roof installation, I was originally planning on using MC4 splitters to combine two panels in parallel right at the panels themselves. Then run thw wires back to a single overcurrent breaker in front of my controller.

However, since the current doubles after the connection, the voltage drop was potentially greater than 3% for a long roof run.

Instead, I'm thinking of just running a pair of wires back from each panel -- it'll mean using two overcurrent breakers instead of one, but I won't have voltage drop worries.

Sound right?


  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
    Re: MC4 Parallel Wiring & Voltage Drop

    It does not really matter... If you run a pair of 12 awg wires or one set of 9 awg wires (yes, there are no 9 awg wire commonly available)--The voltage drop will be about the same (wire area doubles about every 3 awg). So, a pair of 12 AWG or one set of 8 AWG--The 8 AWG will have a bit less voltage drop because it is >2x the wire area) and it will cost 2+x as much (mostly, you are paying for the copper).

    If you have 3 or more panels in parallel, you should have a series protection fuse for each panel before they are bused together.

    And, lastly, if you are having issues with too much voltage drop, there are MPPT controllers which allow you to put two (or sometimes more) panels in series--Cuts the voltage drop down dramatically.

    All About Charge Controllers
    Read this page about power tracking controllers

    And here are a couple smaller/lower cost (but very good quality) MPPT charge controllers:

    Morningstar SunSaver 15 Amp MPPT Solar Charge Controller
    Rogue 30 amp 12/24 volt MPPT


    PS: An option to using the MC4 Y connectors--You can buy short lengths of Male/Female MC4 cables too... Plug into the panels and wire the cut ends into the balance of your wiring:

    8 Foot MC4 Extender Cable Male/Female

    and you may want an MC4 tool to pop apart the mated MC4 connectors:

    Disconnect Tool for MC4 Connectors (set of 2)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset