[active1]

I would say yes.
The 125a CB protects the feeder (assuming it's sized correctly).
The 200a CB would provide a separate structure main disconnect.
The 200a buss would be able to handle an excess load from 2 sources, the 125a main and the PV source. Again I don't know what the solar output is, but am guessing it's less than 75a.

 

[dham206]

I would say yes.
The 125a CB protects the feeder (assuming it's sized correctly).
The 200a CB would provide a separate structure main disconnect.
The 200a buss would be able to handle an excess load from 2 sources, the 125a main and the PV source. Again I don't know what the solar output is, but am guessing it's less than 75a.

Im now thinking of buying a 200 amp panel and changing the main breaker to a 125 amp. That way if it the main trips its not downstream and can be easily reset inside the DADU. Its also going to cost me more money to buy a separate 125 amp breaker. Id like to just keep the 200 amp breaker if code allows me.

 

[eddy current]

I am installing a meter base on a house that has 2 breakers feeding sub panels. One is a 200 amp breaker feeding a sub panel for the main house. The other is a 125 amp breaker feeding a DADU (detached mother in law). The DADU is going to have solar panels. The solar guys want at least a 150 amp rated bus on the DADU's sub panel. Because this is a detached building it needs a main breaker. My question is, Can I have a 125 amp breaker feeding a sub panel that has a 200 amp main breaker in it? 150 amp is uncommon and this is the only thing i can come up with to meet solar requirements.

I'm curious why the solar guys want a buss rated at 150?

 

[HackWork]

Im now thinking of buying a 200 amp panel and changing the main breaker to a 125 amp. That way if it the main trips its not downstream and can be easily reset inside the DADU. Its also going to cost me more money to buy a separate 125 amp breaker. Id like to just keep the 200 amp breaker if code allows me.

There is no guarantee that the 125A breaker in the panel will trip before the feeder breaker.

This is a very common installation. Just install a panel with a 200A breaker.

 

[HackWork]

I'm curious why the solar guys want a buss rated at 150?

A misunderstanding of the 120% rule?

I haven't paid much attention to solar code...

 

[active1]

Hack is right. If you put a 125a main it the other building it would not always be the 1st to trip. The meter could trip 1st, both, or the other structure 1st. If I was to bet, it would be both. Even if you tripped it several times it could be different results from micro variables not worth discussing.

It is a solar code to have the buss sufficient capacity for 2 different sources of power. The idea being a person could draw more than 125a between the sources and overload the buss without overloading the MCB. Another option would be to downsize the MCB to 100a, if calculated load permitted. And if combined the power feeding was 125a or less (100a MCB + 25a solar).

Going off memory and sorry I don't have the article handy.