Wire Gauge Question

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opensky
opensky Registered Users Posts: 13 ✭
in Solar Beginners Corner #1
I'm new to solar and I'm having trouble determining what gauge of wire I need to go from the combiner box to the controller I have Sun Electronics panels - 200w, 33.2V Open circuit, and 7.28A. I'm wiring them in 2 series of 3. So the voltage will be 99.6 and the amperage will be at 14.56. The distance from the combiner box to the Outback FM60 is about 120 feet. I'm thinking I'll need either 4, 5, or 6 gauge. Also, this will show my ignorance but, will stranded wire work or does it need to be solid?

While I'm at it, I should back up. How should I get the pv cables to the combiner box? I was planning on putting the combiner box inside which means putting it about 30 ft from the panels. First off, is that pointless? If not, should I run four separate pv cables (two positive and two negative) and connect them at the combiner box? Or should I reduce to two at the panels and run two to the combiner box?

THANKS!
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
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    Re: Wire Gauge Question

    welcome to the forum,
    i would like you to clarify the vmp of the pvs as the v drop calculations aren't involving the voc so i couldn't read very far into your post as i thought it incomplete for information from the start. the voc is helpful in determining how many pvs you could place in series for use with that cc. also verify for me that the 7.28a of current is the imp.
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  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    #3
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    Re: Wire Gauge Question

    Hi the fm60 manual has some charts giving wire sizes and distances. If you haven't bought the fm60 yet you can download it from the Outback site.
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
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    Re: Wire Gauge Question

    opensky,
    i took the trouble to look up the info on the pvs and they are 27.5v vmp and 7.28a imp. i ran the calculations that included the 21ft length of #11 (4mm^2) pv interconnecting wire. (that 21ft length is probably going to need to be a bit more as you need to adapt to go to the combiner) this will be for a single pair of wires running to the cc from the combiner. if using #6 you will see in the area of 2.45% v drop. if you are looking to keep it below 2% then go to #4 as that is 1.65%.

    if you think you might add another string in the future for a total of 3 strings of 3 pvs and used the #4 then this expansion would put you at 2.31%. #2 would be seen as about 1.6% for 3 strings of 3 pvs and that same #2 would show about 1.2% for 2 strings of 3 pvs. btw, i would not use #6 for 3 strings of 3.

    i hope i did this right as i'm pretty tired right now, but it should give you a good idea what you want to do.
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  • Frxddy
    Frxddy Solar Expert Posts: 113 ✭✭✭✭
    #5
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    Re: Wire Gauge Question

    I trust when talking wire sizes we are referring to copper wire? I wouldn't want a newbie to get confused and use aluminum without knowing the relationship between the two.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
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    Re: Wire Gauge Question
    Frxddy wrote: »
    I trust when talking wire sizes we are referring to copper wire? I wouldn't want a newbie to get confused and use aluminum without knowing the relationship between the two.

    correct as we always refer to copper wire unless we say otherwise.
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  • drew4justice
    drew4justice Solar Expert Posts: 36 ✭
    #7
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    Re: Wire Gauge Question

    Regarding your queston about moving the combiner inside--I believe that it's a national code requirement for any DC electrical conductors to be placed in metal conduit rather than plastic when entering the building, to the point of AC conversion.

    I'm not trying to pass inspection myself, but I'd like to be closer to code than further from it. Had I known this when I installed my panels, I would have done things differently.

    Also, I have suspicion that you obtained your panels from Florida? If so, those panels are probaby "C" grade and they won't produce the numbers for which you see them rated.

    Drew
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  • opensky
    opensky Registered Users Posts: 13 ✭
    #8
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    Re: Wire Gauge Question
    niel wrote: »
    opensky,
    i took the trouble to look up the info on the pvs and they are 27.5v vmp and 7.28a imp. i ran the calculations that included the 21ft length of #11 (4mm^2) pv interconnecting wire. (that 21ft length is probably going to need to be a bit more as you need to adapt to go to the combiner) this will be for a single pair of wires running to the cc from the combiner. if using #6 you will see in the area of 2.45% v drop. if you are looking to keep it below 2% then go to #4 as that is 1.65%.

    if you think you might add another string in the future for a total of 3 strings of 3 pvs and used the #4 then this expansion would put you at 2.31%. #2 would be seen as about 1.6% for 3 strings of 3 pvs and that same #2 would show about 1.2% for 2 strings of 3 pvs. btw, i would not use #6 for 3 strings of 3.

    i hope i did this right as i'm pretty tired right now, but it should give you a good idea what you want to do.

    Thank you so much for taking the time to do that.
    That's a good Point, I definitely hope to expand in the future.

    Where's the best place to find #4 (and/or #2) wire?
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #9
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    Re: Wire Gauge Question
    opensky wrote: »
    Thank you so much for taking the time to do that.
    That's a good Point, I definitely hope to expand in the future.

    Where's the best place to find #4 (and/or #2) wire?
    Electrical supply house.
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