Progress Energy question for 22K, residential Tier 2 installation

[ggunn]

InnerS.,
Also, do you realize what the point of the 4 main breakers is, w/o a single main breaker?
The 120% rule will not apply here to the Buss - under any interpretation of the code, unless you have a buss fed from both ends ( e.g main breaker and pv breaker(s) ) . With 4 pv breakers all as main breakers there is no current that needs to be added going both ways, ie. no 120% rule to apply.

Which makes absolutely no sense to me. If there is no main breaker on a panel connected to the service via a line side tap, there is no limit, other than the size of the service, to the current that can be supplied to the bus by the service.

If we limit the available current from the service with a main breaker, then by the 120% rule the bus has to be rated to carry the main breaker current plus the inverter current divided by 1.2, but if there is no main breaker it only has to be sized to carry the inverter current divided by 1.2? Does that make any sense? Am I missing something?

Most of the code is written with only the current flowing from the service out to loads in mind; sometimes you have to stand on your head to interpret how it pertains to current flowing the other way.

 

[jaggedben]

Which makes absolutely no sense to me. If there is no main breaker on a panel connected to the service via a line side tap, there is no limit, other than the size of the service, to the current that can be supplied to the bus by the service.

If we limit the available current from the service with a main breaker, then by the 120% rule the bus has to be rated to carry the main breaker current plus the inverter current divided by 1.2, but if there is no main breaker it only has to be sized to carry the inverter current divided by 1.2? Does that make any sense? Am I missing something?

If there is no main breaker it has to be sized to carry the inverter current. (No dividing by 1.2).

I agree with you on the general point that it doesn't make much sense. The 120% rule makes (some) sense for panels that are all loads except for a solar breaker or two, but not for panels that are supposed to be dedicated to solar. The question is whether the code can be made to account for that.

 

[GoldDigger]

The question is whether the code can be made to account for that.

And also whether it already does that by referring to all of the breakers in circuits "supplying power to a busbar or conductor". If no power is being drawn from the busbar (inverter connections only and ignoring the miniscule drain while waiting to qualify the network power or waiting for solar input to reach a minimum) then is the main breaker actually supplying power?
705.12(D)(2) [2011].

 

[BillK-AZ]

If there is no main breaker the cables from the service to the disconnect are a Service and need to be sized according to the rating of the disconnect, not the inverter breaker. Cables after the disconnect are sized according to the OCPD of the disconnect which is in turn sized according to the inverter requirements. Minimum service disconnect is 60A as others have mentioned (230.79(D)).