PV Install main derating and new circuits questions

I am signed up for a solar installation, but I have not gotten a site inspection yet.
I wanted to educate myself with some degree to protect myself during any issue that may arise.

They mentioned (sales guy, not electrician yet) the need to derate my system from 125A main breaker to 100A to gain 50 more amps using the 125% rule. Doing my own investigation online... I believe that the 7040kw system will need 30amps. 

My concern is that I don't have any available breaker circuits for the inverter and the only way to install one would be to merge (see image) the bottom 2 breakers into the upper 2 to gain space, which would mean my entire interior and garage 120v would be tied together. Lastly, I wanted to add a 32amp (50a breaker) for a future electric vehicle. Do I have any options to utilize a sub-panel or other various alternative, or am I forced into an upgrade 200amp panel? I am not looking to anything outside of code, I only want to have some internet knowledge from the community once the electrical site inspection happens.

much appreciated.


  • mvasmvas Registered Users Posts: 384 ✭✭✭
    edited October 2019 #2
    I doubt that you are installing a "7040 kw" system
    Maybe, a 7,040 watt PV system or a 7 kw PV system ?

    How did you calculate that a 30 Amp Breaker is OK for your 7 kw Inverter?
    show your math ...

    Your "Center-Fed' Main Panel is problematic
    There are special rules for sizing the PV Breaker with a "center-fed" Main Breaker

    I doubt that you can derate the Main Breaker from 125 Amps, down to 100 Amps.
    I doubt that you can add a 50 Amp breaker for an electric vehicle
    I doubt that you can "merge" the load wires from the bottom two breakers, into the upper two breakers

    You may need to consider...
    a)  a new 200 Main Panel with an end-fed Main Breaker or
    b) A Supply-Side connection for the PV Inverter connection
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