What's the limiting factor in upsize the bus bars for PV backfeed?

[PVJon]

In order to accommodate larger PV backfeeds, we have done several installs with CH's "solar read" 225 amp panel that comes fitted with a 200 amp breaker. This gives us 70 amps of PV breaker backfeed where we normally only have 40. So what is the limiting factor on this strategy? Can I take a 125 amp service... upsize it to a 200 amp panel... use a 125 amp main breaker and then get 115 amps (75+40) of PV breaker backfeed?

 

[mpcarnahan]

correct

correct

the only limiting factor is the 120% rating on the bus, and the location of the PV backfed breaker.
So yes, as along as the MB and PV breaker do not exceed 120% of the bus rating, your fine.
I've put in 800A panels with 600A MB for just that reason.

 

[PVJon]

Thank you!

 

[BillK-AZ]

The other limit is the service rating, you can not exceed the 125A in this case.

 

[Sierrasparky]

The other limit is the service rating, you can not exceed the 125A in this case.

The OP states that could he replace the 125 with a 200.
The only caveat is if the scenario is ok the AHJ and the POCO. I don't see the issue as even if the service conductors are not up sized the back feed is still less than the service rating. This formula and code is a panel buss rating not a service entrance size limitation.
What I wonder is if some idiot would place a larger breaker in the panel.

 

[jaggedben]

Another limitation, which may be obvious, is that the PV breaker can't be bigger than the main. While not a code violation per se, it simply won't work, because the main will trip if the PV produces at full output.