EG4 12kPV with 200A main panel

[johnplanetz]

We currently have a 3.78kw solar system installed in 2019- with Delta grid-tied inverter and 20A backfed breaker on the main panel. I'm planning to remove this inverter, and upgrade to an EG4 12kPV, and in the future add battery and more PV panels.

Our home has a 200A main panel (pics attached). There is no main breaker on the panel, but there is a group of 125A sub-feed lugs which I don't really understand.

Thinking about the NEC 120% rule, the EG4 12kpv has max output 33.3A. 33.3Ax125% is 41.6A, so I think we're supposed to replace that 20A solar breaker with 45A, but that would exceed 120% of a 200A panel. So I guess we'd need to derate the panel? Or are those sub feed lugs already derating the panel to 125A? OR- should I simply use a 40A solar breaker and call it a day?

 

[johnplanetz]

Here's a followup pic of the subfeed lugs with the panel removed. The cables from those subfeed lugs are bent 90 degrees towards the back, then 90 degrees again to head directly left behind the bus bar towards the meter. So I guess they are the main service connection.
I read elsewhere that this type of panel with no main breaker was allowed back in the day- as long as all the power could be switched off with at most six breakers. Downside is no way to de-energize the bus bar without pulling off the meter.

 

[johnplanetz]

Any thoughts on that 40A solar breaker, vs derating the panel?

 

[TM48]

What size breakers do the subfeed lugs feed? As far as the 40 amp I'd do it and if called on it you could down size the charger circuit to 50.

 

[Stephen InGeorgia]

Look at the diagrams and explanations for the 12k here: https://eg4electronics.com/wp-content/uploads/2024/09/EG4-12kPV-Wiring-Diagrams.pdf To be 100% square, you can have EG4 'de-rate' your inverter if needed to comply with the 120% rule. I'd use a 40A breaker and appropriate wire size for 40A.

 

[johnplanetz]

@TM48

What size breakers do the subfeed lugs feed?

I'm still not sure I'm understanding those subfeed lugs properly, but it seems that they are the main connection from the meter, in lieu of a main panel breaker. So the electricity comes from the street, through the meter, to those subfeed lugs onto the bus bar here. Then the panel has the other breakers as shown: 100A breaker to the sub panel in the garage, 50A hvac breaker, 15A breaker for the garage-door/attic-fan, 60A breaker for EV charger, and the 20A breaker for solar (to be replaced).

So to completely turn off the power to the property, you have to switch those 5 breakers off. Conceivably, we could take off those subfeed lugs and replace it with a big 200A breaker, but I guess that doesn't really accomplish anything other than making it easier to turn off the power.

Do you think I'm understanding this right?

As far as the 40 amp I'd do it and if called on it you could down size the charger circuit to 50.

Would lowering the EV charger breaker to 50 help with the NEC 120% rule? It's not clear to me that the other breakers on the panel have anything to do with the calculation...

 

[johnplanetz]

Look at the diagrams and explanations for the 12k here: https://eg4electronics.com/wp-content/uploads/2024/09/EG4-12kPV-Wiring-Diagrams.pdf To be 100% square, you can have EG4 'de-rate' your inverter if needed to comply with the 120% rule. I'd use a 40A breaker and appropriate wire size for 40A.

Got it. That makes sense!

Followup question: we'd like to later upgrade the setup with PV-backup of the house and battery-backup. So, I think we'll need to remove the 100A garage-sub-panel breaker in the main panel, and connect those subpanel wires instead to the 12kpv's LOAD terminal (possibly through a new wall panel with the 100A breaker in it). Sound right so far?

What's not clear to me is the relationship between this 100A critical load subpanel , and the 40A solar backfeed breaker mentioned above. Would the 40A solar breaker at the main panel limit total continuous power from grid to the house (through the LOAD terminal) to 40A?

Thanks @Stephen InGeorgia !

 

[CAGNome]

Got it. That makes sense!

Followup question: we'd like to later upgrade the setup with PV-backup of the house and battery-backup. So, I think we'll need to remove the 100A garage-sub-panel breaker in the main panel, and connect those subpanel wires instead to the 12kpv's LOAD terminal (possibly through a new wall panel with the 100A breaker in it). Sound right so far?

What's not clear to me is the relationship between this 100A critical load subpanel , and the 40A solar backfeed breaker mentioned above. Would the 40A solar breaker at the main panel limit total continuous power from grid to the house (through the LOAD terminal) to 40A?

Thanks @Stephen InGeorgia !

Apparently they've updated their literature recently, like this week. I was doing research last week and came across the same installation diagram you did. I called them for clarification as I'm an electrician and having a 60-200amp critical loads panel downstream a 40amp breaker didn't sound correct. Now it appears they've gotten UL listing for Busbar PCS which allows a backfed breaker to be sized larger than the 120% rule as long the conditions are met. I'll ordering my system this week now that I know I can pass more than 40A thru the crit load panel