Assistance please on PV capacity restrictions and 120% rule.

[bilede]

I have been trying to figure out a few things on a residence for solar and seems each direction is not uncomplicated. I have read and read and can't seem to answer a couple questions so I am providing a wiring layout and my questions and hopefully the experts can help me out as I would appreciate it very much. Home is on five acres and includes main house with combo 400/320 meter box, a remote 200 amp subpanel, and two outbuildings both with 125amp subpanels which I need to connect separate solar arrays on. See attached image for details I thought were pertinent.

My questions;

Does the main box carry a 400 or 320 amp rating used to calculate the size of array it can support or is it based on a portion since it has two 200 amp main breakers when calculating the 120% rule?

What is the maximum array size in amps I can connect to the two end subpanels given current layout? On diagram I put a red breaker where I am thinking I would connect the two solar systems each on a different building.

As stated, main combo box is a 400/320amp combination with a single meter. All described wiring already exists. Must I have a disconnect other than the circuit breaker that leads to the subpanel leg that the solar is connected to? Obviously, desire is to plug in system with a new breaker in the end subpanel and not have to rewire everything around the main box as its limited in space around the box and wiring is pretty tight and not going to lend itself to rerouting to other boxes at its location. With auto shutdown, microinverters are going to shutdown as soon as meter is pulled so box goes cold.. is more needed?

Thank you.

House wiring layout.jpg

[solarix]

OK, the backfeed rule is 20% of the buss rating. The main 400A box is really a dual 200A, so that limits to 7.7kW backfed into either of its busses.
But you want to use the 100A subpanels, so that is 20A backfed or 16A continuous which is a 3.8Kw ac and the 125A panel could use 4.8kW ac.
But, most utilities require a single disconnecting means so having two separate solar systems is a problem. Usually, a dual system has an AC combiner panel to feed all the solar power into one safety disconnect switch.
What I like to do in this situation, is do a load-side tap into the 2/0 wire feeding the 200A subpanel - but only if that panel has a 200A main breaker in it to protect it.
Otherwise, you have to do a line side tap in the main panel and add a third main disconnect as I suspect you want more like a 15kW solar array. Probably means pulling new wire from the remote roofs.
Sorry for the bad news, we deal with this all the time....

[nerdralph]

I didn't realize it was only 120% in the NEC. With the CEC, it's 125%:
notwithstanding Section 14, for a dwelling unit, the sum of the ampere ratings of the overcurrent devices in source circuits supplying power to a busbar or conductor shall be permitted to exceed the busbar or conductor rating to a maximum of 125% of the rating of the busbar or conductor
CEC 64-112 4) d)

So with a 200 Amp bus we can use a 9.6 kW inverter.

[foggysail]

I didn't realize it was only 120% in the NEC. With the CEC, it's 125%:
notwithstanding Section 14, for a dwelling unit, the sum of the ampere ratings of the overcurrent devices in source circuits supplying power to a busbar or conductor shall be permitted to exceed the busbar or conductor rating to a maximum of 125% of the rating of the busbar or conductor
CEC 64-112 4) d)

So with a 200 Amp bus we can use a 9.6 kW inverter.

Don't rely on the main breaker sizes, verify the load center's maximum amperage to determine the 120 rule. But Solarix above posted what could be a gutcha with the single disconnect ruling by utilities..............I have not checked to see if NEC also has that requirement.