Remote combiner box vs. separate homerun from PV

Ravs
Ravs Registered Users Posts: 13 ✭
in Solar Beginners Corner #1
I am waiting patiently for my PV equipment to arrive, but in the meanwhile I have been poring over all the great posts and information on this forum and it has helped me understand most of the basics of a PV system.

My system will be a 5.67 kw system comprised of 6 x 3 strings of 315 watt panels and an SMA 6000 grid tied inverter, somewhat oversized to allow peak production on frigid Minnesota days.

If I have the choice, why would I ever want to have a remote combiner box if there are sufficient terminals on the inverter itself to homerun each of the three strings? Conductor length should not be an issue (<50 feet), and why invite another connection? Just curious what the consensus is out there, or if combiner boxes serve other purposes other than simply a parallel connection of all three strings. Seems like the sizing tools on the inverter websites promote multiple strings. Isn't is all simply about meeting the input current and voltage requirements at the inverter and nothing else? I used to think that the individual string terminations at the inverters actually were tracking separately strings, but that is not the case.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #2
    Re: Remote combiner box vs. separate homerun from PV

    I know my combiner box fuses each string before it combines them.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,641 admin
    #3
    Re: Remote combiner box vs. separate homerun from PV

    NEC/Building Codes requires that for 3 or more strings connected in parallel, each string requires a Series Fuse or Breaker rated per the solar panel's data sheet.

    Because solar panels are power sources (sort of like batteries), when three or more strings are wired together, the fuses protect each string, if it gets a short, from being over current supplied by the other two or more parallel connected strings.

    For two parallel strings (or just one series string), no series protection fuses are required.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • bart
    bart Solar Expert Posts: 30 ✭
    #4
    Re: Remote combiner box vs. separate homerun from PV

    One part of his question was missed.

    Is there an advantage or not (code or otherwise) to mounting the combiner box on roof next to PV or mounting next to inverter below?

    Bart
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,641 admin
    #5
    Re: Remote combiner box vs. separate homerun from PV

    From the otherwise point of view--mounting the combiner box on the side of the home where you don't need a ladder to access it -- a plus.

    Also, if you can keep direct sun and rain of off the box--you should have less corrosion and mechanical failures (circuit breakers and even fuses are very easily damaged by water and heat).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #6
    Re: Remote combiner box vs. separate homerun from PV
    bart wrote: »
    One part of his question was missed.

    Is there an advantage or not (code or otherwise) to mounting the combiner box on roof next to PV or mounting next to inverter below?

    Bart

    From an electrician's POV; If I had to work on the system, it would irritate me no end if I had to keep climbing up and down a ladder to get to the combiner while working on the rig. So I'd prefer it on the roof where it's handy.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #7
    Re: Remote combiner box vs. separate homerun from PV
    bart wrote: »
    One part of his question was missed.

    Is there an advantage or not (code or otherwise) to mounting the combiner box on roof next to PV or mounting next to inverter below?

    Bart

    When you say "inverter below" is your inverter on the roof under the panels, or on a wall, where it can be reached by standing on the ground ?

    I'd prefer to stand at ground level, and never use a ladder after the install, if homeruns came to a ground accessible box, I'd be very happy. Sure, you pay a bit more for the wire, but the time saved not having to get on the roof, is worth it to me.


    PS-
    got the water pump wired and plumbed:
    With so much rain this year, trenches have not been able to be dug. We finally had a break, and got them in. Roger and Mike helped glue over a mile of pipe (several runs in the same trench, 240V power, pond water, drinking water, signal for tanks full) the contractors stuffed it into the trench and covered it back up. We'll have 9,000 gallons of stored irrigation water & fire hydrant supply, and 3,000 of drinking water.

    Water & Power Trenches (+900')
    http://www.facebook.com/album.php?aid=2046878&id=1196643274&l=5f0faaf572
    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

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    gen: http://tinyurl.com/LMR-Lister ,

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