combiner box

I want to add another 50 watt panel to my small system. Do I need a combiner box? My GE panels come with junction boxes, can I just run the + - of panel "B" on panel "A" then from Panel "A" +- to the charge circuit braker or fuse?

If I have to use some sort of combiner, can I use this puppy?

what are the advantages/disadvantages of not having a combiner box?
On the GE spec sheet it has "Maximum Series Fuse Amps 5" is 5 amp the size I should use for a fuse per panel? If I do parallel the panels w/o a combiner box? what fuse amount would I use?

Thanks in advance.


  • mike95490mike95490 Solar Expert Posts: 8,207 ✭✭✭✭✭
    Re: combiner box

    Tell us more of what the rest of your small system is. What are the models of the other panels, what is your charge controller ?

    My first wild guess is you don't need a combiner, but I've been wrong before.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • BB.BB. Super Moderators, Administrators Posts: 28,880 admin
    Re: combiner box

    The idea is to prevent solar panel failures (i.e., fires) if there is an internal short in one panel when it is connected to a large parallel array (one shorted panel and a bunch of other panels driving current into the short--or a shorted battery controller).

    In your case, just add an inline 5 amp fuse going out to each panel. Might have to home run all the panels to one location where it is easy to wire everything.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: combiner box

    by the way it is how you are talking, i'd say you have 1 50w pv now and are adding the 2nd to it. if the controller can handle the extra power there is nothing wrong with one pv feeding into the original and then off to the controller. you can combine on the inside of pvs that have accessible junction boxes. one thing you will have to watch for is that you would now have double the current flowing on the original wires to the controller. the voltage drop calculator in the sticky would help you in determining if your wiring is ok or needs upgraded because of this extra current being carried.
    now in the case of daisy chaining many paralleled pvs the combiner would be a better idea. i see nothing wrong with using the one you point out, but it should be in a weatherproof enclosure for obvious reasons unless the combining is done inside of your home.
    edit: do note the negative has to be combined too, but it doesn't need the fuses. the following is an option for those connections:
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: combiner box

    I've used this Blue Sea Systems product (#5015) before. It's ~$35 plus shipping from West Marine (

    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: combiner box

    Thanks guys,

    Niel, for my wires I will be using the MC connectors w/ the 50 ft wire extension cut in half. The cut ends will be pigtailed to connect to my Blue Sky controller and the other end to the panel. The wire run is only 25 ft, do you still think I might have an issue w/ the wire size (#10)?

    Crewzer - thanks for those links.

    FYI - I have 50 watt GE panel, Blue Sky controller w/ remote IPN, MK 200 AH battery, 600 W inverter.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: combiner box

    if i'm reading you right that the total + and - wire lengths will be 50ft this will be just over 3% voltage drop percentage for 2 50w pvs. ideally, you should like to get that % lower, but it will work. if the run is 50ft (50ft + and 50ft -)then no, it's way to long for the amount of current carried that i estimated at about 7amps for both 50w pvs.
  • System2System2 Posts: 6,290 admin
    Re: combiner box

    sorry 50 ft cable cut in half to give me 25ft- 25ft+
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