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  • Combiner Box and Breakers

    Greetings everyone
    I need some direction on this one... I'm going to have 3 strings going into a combiner box, each is to have it's own 15 amp breaker, once combined (max of 9 amp each), I was going to run some # 6 wire in conduit back to a din mounted 50A breaker before going to the charge controller. I know the # 6 wire is over-kill.

    My question is this: Instead of having the 3 breakers in the combiner box, would it be acceptable to return all three strings to my panel area in the basement (with smaller gauge wire) and mount the string breakers there?
    Do you ever need to re-set a string breaker?

    Thanks in advance
    Jan

  • #2
    Originally posted by JanS48 View Post
    Greetings everyone
    I need some direction on this one... I'm going to have 3 strings going into a combiner box, each is to have it's own 15 amp breaker, once combined (max of 9 amp each), I was going to run some # 6 wire in conduit back to a din mounted 50A breaker before going to the charge controller. I know the # 6 wire is over-kill.

    My question is this: Instead of having the 3 breakers in the combiner box, would it be acceptable to return all three strings to my panel area in the basement (with smaller gauge wire) and mount the string breakers there?
    Do you ever need to re-set a string breaker?

    Thanks in advance
    Jan
    DC breakers are very different beasts compare to AC breakers and much more expensive. Are you sure you need them in the first place or you're simply calling fuses as 'breakers'? Usually fuses are used to prevent fire when one string develops short and 2 others feed it through the common point in combiner. IMO it would make no difference where you put fuses on each string as long as they are well isolated from each other before common point.

    Comment


    • #3
      Yes, you can run the PV wiring to the location of your choosing for the combiner box. Just measure the length of the run and note wire size then check power lose on a voltage drop calculator. Try to keep loses less than 3 percent. The less the voltage drops the more power you get to the controller. Longer runs may require a higher PV voltage or a larger wire size. Also DC circuits need to be in their own enclosure unless it is in an approved epanel.

      A string breaker offers not only safety and protection, but is also a handy switch for troubleshooting and testing.
      Last edited by Raj; 09-11-2017, 04:31 AM.
      3.6 kw PV, Classic 150, Radian GS4048A, LFP 195A

      Comment


      • #4
        Originally posted by max2k View Post
        DC breakers are very different beasts compare to AC breakers and much more expensive. Are you sure you need them in the first place or you're simply calling fuses as 'breakers'? .....
        Let me suggest a different viewpoint. DC breakers only, no fuses. Many fuses/holders are not rated to be Interrupters. That means you can't "pull the fuse" to turn something off, the fuse will drag a welding arc across the holder.
        Midnight Solar supplies Switch Duty rated breakers for about the same cost as a fuse & holder, and it is many times more convenient to use to power down something, check 1 string at a time (all strings should produce the same power, easy to locate a bad string) and useful for rebooting the Controller.

        In the winter, I had 1 string breaker trip. Cold clear air, and bright sun can deliver high power to cause a nuisance trip. With breakers, it was easy to discount a fault had occurred.
        Powerfab top of pole PV mount (2) | 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

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

        Comment


        • #5
          Thanks so much for the replies.
          I was leaning towards string breakers as mike90250 seemed to suggest. I've done quite a lot of electrical work over the years both home and marine. I'm not a fan of fuses frankly. I also like the idea of being able to trouble shoot things easily. To be clear Solar is totally new to me do bear with my questions please.

          At the beginning of the post I was just unsure where was the best place to have the string breakers, I know I can mount them in the combiner box but I'm leaning towards running the strings back to my area in the basement where the solar controls will be. It should not be too difficult, the run from roof combiner box to the basement is approx 35 ft. I'll have to pull 3) 10 gauge wires - one for each string - the max amps for each string is 9 at approx 110 volts. I'll tie all the negative leads together in the combiner box and bring that back via a # 6 gauge wire. For the ground I was planning on using a # 8 or 6 gauge wire.

          The only down side to this config is that I'll be using a combiner box on the roof that really won't combine anything - it will just be a transfer box, Then I'm going to need a DC (din ?) breaker box in my solar control area of the basement prior to going into the charge controller.

          Regarding that, I had a recommendation from Wholesale solar to use a BigBaby box with two breakers - one going to the charge controller and another between the controller and the battery bank. BTW - this is going to be an off-grid system. [ 48v with 380 AH battery bank ].

          All that said the output of the three string breakers will feed the single (50A) breaker going to the charge controller.

          Does all that sound reasonable?

          Thanks again.
          Jan

          Comment


          • #6
            I was able to use a 6 position box, for both my combiner and controller & inverter breakers.
            https://www.facebook.com/12021279471...854757/?type=3

            Powerfab top of pole PV mount (2) | 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

            solar: http://tinyurl.com/LMR-Solar
            gen: http://tinyurl.com/LMR-Lister

            Comment

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