I don't think I would measure the second 200A panel. The Gridboss does not require CTs as it has internal measurements. While on-grid it would just think it's a 200A system. I don't need zero export or PCS in this scenario for any compliance reasons.
When the grid fails, this would be a 200A bus limited system since one 200A panel would be feeding other one. I wouldn't need PCS off-grid, either, since the stacked inverters and GridBOSS aren't capable of delivering that much current anyway. One concern that I need to think through is neutral wiring. On-grid I would have the 200A grid neutral, but in standalone mode a 125A neutral would be coming from the other 200A load center. This creates a parallel neutral situation since the neutral isn't switched. I'm not sure yet what the implications are of that. I'm going to draw it up to wrap my head around it. Jason Szumlanski Principal Solar Designer | Florida Solar Design Group NABCEP Certified Solar Professional (PVIP) Florida State Certified Solar Contractor CVC56956 Florida Certified Electrical Contractor EC13013208 On Thu, Feb 5, 2026, 8:39 PM Chris Sparadeo <[email protected]> wrote: > I like the ingenuity, Jason. I would assume you would still need to CT the > other half of that 320A service for whole site monitoring requirements. If > the total service is pulling more than 160A I am wondering if the PCS would > try to limit battery charge/discharge to prevent overload on what the EMS > is thinking is a 200A bus bar. To be fair, that would be quite a load, even > on a 320A service… > > On Thu, Feb 5, 2026 at 6:25 PM Jason Szumlanski via RE-wrenches < > [email protected]> wrote: > >> I had a thought. What about just backing up one of the two 200A panels >> with an off-the-shelf residential MID, and install an automatic transfer >> switch on the other 200A panel with the primary source being the grid, and >> auxiliary source being the inverter output, possibly through a feeder from >> the first 200A panel. >> >> This would allow backup of all loads on a single 200A MID. I would comply >> with 710.15(A) (NEC 2020) without any required load management. >> >> Better yet, make the auxiliary source for the second 200A panel a feeder >> from a smart load breaker in the MID for load management purposes. The EG4 >> GridBOSS can send a 125A feeder to the other panel. That would be more than >> sufficient for practical purposes in a grid outage. >> >> >> Jason Szumlanski >> Principal Solar Designer | Florida Solar Design Group >> NABCEP Certified Solar Professional (PVIP) >> Florida State Certified Solar Contractor CVC56956 >> Florida Certified Electrical Contractor EC13013208 >> >> On Thu, Feb 5, 2026, 8:48 AM Jay <[email protected]> wrote: >> >>> I reread your question. >>> >>> I think the only way to be sure the internal transfer switches in the >>> inverters all switch at the same time on a big high load ( exceeding >>> potentially the max current rating of a single relay) multi stack inverter >>> system is to use external transfer switch’s. >>> >>> The system I installed is never going to exceed 200 amps, probably never >>> exceed 80 amps. 2 inverters can more than handle the load. The 3rd was >>> installed as built in redundancy to make it easier in case one fails. As >>> the system won’t run on 1. So I didn’t have to worry about exceeding relay >>> capacity. >>> >>> I think this is one of the potential problems with paralleled systems vs >>> larger single 120/240 inverter’s which we don’t really have here in the US. >>> >>> >>> >>> On Feb 4, 2026, at 7:05 PM, Jay <[email protected]> wrote: >>> >>> >>> I have a 3 stack eg4 18k and while watching the inverters online they >>> are totally balanced. >>> >>> Jay >>> >>> On Feb 4, 2026, at 4:29 PM, Jason Szumlanski via RE-wrenches < >>> [email protected]> wrote: >>> >>> >>> Hi all, >>> >>> When backing up a 400A service with multiple paralleled all-in-one >>> inverters by combining the AC inputs and outputs, the individual inverter >>> transfer switches must operate in a synchronized manner. Come to think of >>> it, the same thing applies to backing up 200A service with paralleled >>> inverters. Are these tested for this function? – I assume so. >>> >>> I'm really asking because Sol-Ark seems to be the only brand that >>> specifically addresses 400A service in documentation, although not very >>> clearly in the manual itself. Their training and literature support passing >>> through additive grid pass-through with multiple inverters, which implies >>> that they are additive in their ability to transfer power. See attached >>> examples. >>> >>> I have not found anything from EG4 (for the 18kPV) or the Midnite AIO >>> that specifically addresses this. >>> >>> In other words, how can we assume that paralleled inverters will be >>> additive in terms of their ability to transfer high levels of current that >>> exceed the rating of a single unit? Is that even addressed in listings? The >>> documentation is quite poor from all manufacturers (no surprise there!) >>> >>> I do have a couple of grid-interactive Midnite AIO systems with four >>> paralleled AIOs backing up 400A services, and so far, so good. My engineer >>> signed off on that. >>> >>> >>> Jason Szumlanski >>> >>> >>> * <http://www.floridasolardesigngroup.com/>* >>> <Image 1171.jpg> >>> <Image 1172.jpg> >>> _______________________________________________ >>> List sponsored by Redwood Alliance >>> >>> Pay optional member dues here: http://re-wrenches.org >>> >>> List Address: [email protected] >>> >>> Change listserver email address & settings: >>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>> >>> There are two list archives for searching. When one doesn't work, try >>> the other: >>> https://www.mail-archive.com/[email protected]/ >>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >>> >>> List rules & etiquette: >>> http://www.re-wrenches.org/etiquette.htm >>> >>> Check out or update participant bios: >>> http://www.members.re-wrenches.org >>> >>> _______________________________________________ >> List sponsored by Redwood Alliance >> >> Pay optional member dues here: http://re-wrenches.org >> >> List Address: [email protected] >> >> Change listserver email address & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> >> There are two list archives for searching. When one doesn't work, try the >> other: >> https://www.mail-archive.com/[email protected]/ >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> http://www.re-wrenches.org/etiquette.htm >> >> Check out or update participant bios: >> http://www.members.re-wrenches.org >> >>
_______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: [email protected] Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. When one doesn't work, try the other: https://www.mail-archive.com/[email protected]/ http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: http://www.members.re-wrenches.org
