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
