Yes, I'm hoping to get some feedback here, as Sol-Ark tech support has a new answer every time you ask them.
I don't love the thought of buying a MID for an off-grid project, but the GridBoss approach seems well thought out. A single generator connection for all paralleled inverters is a nice feature as long as you can accept 200A maximum combined load and three inverters, which should be sufficient for most off-grid homes. The savings in wire size and other distribution components makes the MID a palatable expense, especially in a triple inverter scenario. It also improves serviceability in some ways (although the MID itself is another potential failure point). Next, if we could just get someone to make a 400A MID, we would be in dreamland territory 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 Tue, Jun 17, 2025, 6:36 PM Chris Sparadeo <[email protected]> wrote: > Jason, > > This is a great question. I was waiting for responses, because I’ve > thought this as well. > > Typically I have sized load conductors to either Sol Ark output or gen > output, depending on which was higher, but you are absolutely right that > with grid assist programmed, this number could be higher. Either OCPD or > internal settings could work to avoid upsizing conductors to meet potential > combined amapacity of gen + inverter. However, I’m not crystal clear on how > those settings work for Sol Ark. I know there was a discussion a few weeks > back where Jharen from Sol Ark said it’s possible to derate AC > input/output, but it sounded like the conversation went off line. > > Any insight would be appreciated. > > Best, > > Chris > > On Fri, Jun 13, 2025 at 7:36 AM Jason Szumlanski via RE-wrenches < > [email protected]> wrote: > >> I think there was a previous thread on this, but I can't seem to find it. >> >> I'm wondering how everyone is handling wire sizing on inverter output >> circuits for off-grid systems when there is a generator on the grid input. >> Let's use the Sol-Ark 15K as an example. >> >> Without a generator, it's pretty simple. 80 amp over current protection >> with #4 copper minimum. >> >> With a 20 kW generator that has 80A rated current and 100A overcurrent >> protection, the entire generator current can pass through, so now we are >> talking about a minimum of #3 copper. But is that really the case? Since >> the inverter can be programmed to do grid assist, is it necessary to size >> the conductors for 180A? >> >> It gets trickier in parallel installations. If you have two inverters and >> the same generator, in theory the generator input and output is split >> evenly between the two inverters, so do you size the output conductors for >> 80A inverter output, 130A for inverter plus half of the generator, or do >> you still need to assume 180A? >> >> Assuming the conductors are the same length from the generator to the >> load, in theory the generator pass through should be equal on each >> inverter, but is that really the case? How do we know how each inverter >> will use the generator input and pass through current, especially in a grid >> assist scenario? >> >> I have been erring on the side of caution and simply using 200A >> conductors on the output side of both single and parallel inverter >> installations. The inverter output wire cost, complexity, and difficulty is >> high. >> >> The inverter manufacturers have not made it clear in their documentation >> how grid pass through and grid assist works. >> >> This is one of the reasons that I have started specifying the Midnite >> AIO. With a 100A load breaker, the output load conductor requirement is #2 >> copper per the manual. I assume it is not specified as #3 because it is a >> 100% continuous duty breaker. Regardless, #2 saves a lot of cost and is way >> easier to work with than 3/0 copper. >> >> I am getting ready to specify a parallel EG4 Flexboss21 system using the >> GridBoss to combine them and do load shedding. This seems to be another >> good alternative where the inverter output circuit only needs to be 90A >> rated. The GridBoss can accept a 125A generator breaker, eliminating the >> requirement for pass through all together. This seems like a pretty well >> thought out approach. >> >> >> Jason Szumlanski >> Florida Solar Design Group >> _______________________________________________ >> 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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