Should I have a lower amp breaker?

Solarguy1
Solarguy1 Registered Users Posts: 9 ✭✭
in Solar Beginners Corner #1
Hello,

I have these solar panels (below) which I am hooking up in series. I was sold a MNEPV20-300 breaker (20 amp) with the help from a salesperson here on the website. I am wondering if I should have a lower amp breaker since the current is 8.50 amps in series. 20 amp seems a little high to me. Should I get one instead that is closer to 12 amps? I am figuring 8.5 amps x 1.25 = 10.625 amps... 

As always, Thank you!


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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #2
    Some one from the Northern Arizona Wind and Sun website?

    Perhaps they looked up a different REC 260 watt panel.

    On the back it tells you what you need;

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Solarguy1
    Solarguy1 Registered Users Posts: 9 ✭✭
    #3
    Yes, I gave all info and that's what breaker I was sent. I am just going over everything and noticed it is a 20 amp. So 15 is max, but should I get the 12 amp since that is a little closer to the 10.625 amps target? Or, am I splitting hairs??? 
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #4
    Rolls off the Tongue SPLITTING HAIRS HARES Origin 17th Century

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #5
    Yea, you should get the correctly rated breakers/fuses... Too small of fuse/breaker, you can have false trips. That is just a pain.

    Too large of rating, you run an elevated risk of fire if something gets shorted...

    Note that "heat" goes with the square of the Voltage or Current:
    • Power = Voltage*2 / R = Current^2 * R
    • 15a^2 = 225 a^2
    • 20a^2 = 400 a^2
    So a 20 amp breaker/fuse will allow almost 2x more heating vs the rated 15 amp breaker/fuse.

    The panels are rated/tested against the rated overcurrent protective device. Running outside those ratings is always a risk... And if, heaven forbid, something does "catch fire", your insurance may go over your system with a fine tooth comb to figure out a way to avoid paying out.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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