My read: EG4 likely omitted 15A and 20A because these are contemplated as high-current smart load or AC-coupled inverter ports, not branch circuit protection for small loads. The GridBOSS is sized for things like EV chargers, HVAC, water heaters – not standard household receptables and lighting. They expect those to be regular backup loads. The biggest example I have to support the need to shed a 20A load is a pool pump.
Anyway, when I use a GridBOSS for an off-grid installation, I almost always use Port 4 for a 15A multiwire branch circuit to support a convenience outlet and lighting for the area on one leg and a generator battery charging circuit on the other leg. I see no issue with it. One thing that supports my theory that the breaker ratings are the maximum supported per port is that the ratings in the table overlap. Looking at the table, on line 1, port 1 supports 90-125A breakers, then the table goes on to support 30-80A breakers for port 1. The whole tables is a confusing mess. And what about 35A breakers? 45A? These are common for some mini-split units. They are not in the table, but surely would not be a problem. EG4 needs to revamp this table for clarity. P.S. I have started using Port 1 as the main load port for smaller off-grid jobs without even using the 200A backup load port. I just set port 1 to operate 24 hours a day. This way, you don't need additional overcurrent protection from an external main breaker. The downside is that the manual bypass becomes non-functional, but otherwise it has worked out well for me. 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, Jul 23, 2026 at 9:24 PM Dave Tedeyan via RE-wrenches < [email protected]> wrote: > Hi All, > > I will soon be installing one of these in a detached shed, where it would > be useful to have a light installed. There will be no panel in there other > than the GridBOSS, inverters and batteries. The manual says that the > smallest breaker size that is supported is a 30a breaker. See table below. > > I emailed their tech support to ask if there would be a problem with a 20a > breaker. They gave a very basic answer pointing me back to this same table, > and then recommended to add a subpanel, and then run a 20A circuit from > there. That seems a bit overkill for a light. I cannot see why if a 30A > breaker is allowed, a 20A breaker would not be allowed. It is just a simple > Eaton breaker. Am I missing something here? > > Cheers, > Dave > > [image: image (4).png] > > -- > > > Dave Tedeyan, P.E. > Owner | Sungineer Solar > p: he | him | his > a: 1653 Slaterville Rd. | Ithaca, NY 14850 > w: www.sungineersolar.com <http://www.sungineersolar.com/> > c: (607) 270-0370 > _______________________________________________ > 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 > >
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