Can you please review & give feedback on my Single Line Drawing? (PDF)

MachoDroneMachoDrone Registered Users Posts: 3
I have attached the Single Line Drawing as an image and as a PDF.
Can you please review to see if I have missed any components or if I have OVERDONE anything with redundant parts?
Thanks, so much, for your feedback.


  • MachoDroneMachoDrone Registered Users Posts: 3
    found and error.. there will be a 50A breaker to the outbuildings.. not 40A.. I was only counting 28 panels.
    36panels x 305W each = 10.98kW / 240V = 45.75A
  • BB.BB. Super Moderators, Administrators Posts: 32,318 admin
    edited April 2021 #3
    Nominally, for a 10.987 kWatt system, the average peak harvest (solar noon on cool/clear days) is around:
    • 10,987 Watts * 0.77 panel+controller derating = 8,460 Watts typical best harvest around noon on warm cool spring/fall days
    Current wise, the US/North American standard breakers are rated to "not trip" at 80% or less of rated current. And "will trip" (seconds/minutes/hours) at 100%+ of rated current.

    I always suggest for solar powered system, that you use the NEC derating factor of 80% (or 1/0.80 = 1.25x) because solar panels can supply max/near max current for hours into a MPPT charge controller or Grid Tied AC inverter. Note that the power equation includes line voltage... We can use 240 VAC as nominal, but if you have low line or a Wye 3 phase power system with 208 VAC (3 phase power), you may need to adjust your "base voltage":
    • 8,460 Watts * 1.25 NEC derating for constant current draw = 10,575 Watt branch circuit "derated"
    • 10,575 Watts / 240 VAC nominal line voltage = 44 Amp minimum rated Branch/Breaker rating suggested
    So, 50 Amps is "good".

    Also, one other thing to watch for... If you have long wire runs (from array to meter to pole transformer) and run high line voltage (like 255 VAC or so), then you have to watch for "voltage rise" (aka voltage drop) from GT inverter(s) to pole transformer...

    Say you are 44 amps of #8 AWG for 150 feet, and run 255 VAC high line:

    Using a voltage drop calculator (voltage rise in this case):

    8 AWG @ 150 Feet @ 44 Amps => 8.29 volt "rise"
    255 VAC high line + 8.29 volt 8 AWG rise = 263.29 VAC at inverter

    The typical max line voltage is usually assumed to be 264 VAC... And you should take GT accuracy into account and assume that they may shutdown around 260-262 VAC. Just showing you what can happen (and has happened to a few people with poorly regulated Utility Line Voltage).

    Note the above assumes 8 AWG array to main meter/panel. You would also need to account for the meter to pole (maybe 4/0 aluminum) and the 10 AGW from GT micro inverter string to combiner box... So more calculations (I did max array current over 8 AWG--But if you have different arrays on different circuits, use the 77% derated "actual current", etc. then your calculations will be different than the simplified one I did here).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MachoDroneMachoDrone Registered Users Posts: 3
    unfortunately i pretty much have to redesign everything. I need to add Snow Guards to the roof due to some very slight twists my new gutters have due to ice dams.. so that steels real estate from my roof. Also, the LONGi AC Modules are sold-out. I'll be rewriting the plan and post it in the forum. Thanks for the feedback, so far!!
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