I still haven’t forgotten about the dual transformer question. My EE is coming to the store tomorrow so I’ll run this by him. But, I scribbled up a simple diagram to illustrate my point. See the attachment:
scan.pdf (68.0 KB)
I don’t see this as an issue, but I’ll get a second opinion 
Neutral-ground bonding is tricky and can differ depending on the norms of your local jurisdiction. Here in Ohio, our load centers are indoors, usually in a basement, and the N-G bonding occurs in the main load center. NEC code says it must occur at the point of disconnect, which is our load center. Other parts of the country sometime have external disconnects or might split the utility feed into two sub-feeders before going into load centers. This is likely where an existing N-G bond is made.
If you plan to purchase from a distributor who doesn’t provide detailed wiring diagrams with examples of where and how to perform N-G bonding, then find another distributor. Lots of sellers get by selling to van builders and RVers because they don’t have to fully understand these things.
Please, first check to see if you have a LOCAL, knowledgeable Victron distributor who likes to work with DIYers and can give you good guidance. If you pay them for a little of their time, you will save weeks of frustration, research, or guessing.
We recently had a customer that purchased a system from us for a new off-grid home they built. He followed our wiring diagrams closely, but he added a few extra disconnects and components on the AC side that cost him nearly a week of trying to solve a weird phantom load. Those are almost always neutral-ground bonding issues. Right before I jumped in the truck to go see him in WV, he found the culprit: a bonded neutral in an extra disconnect he didn’t tell us about If he told me he ad-libbed some add-ons, I would have honed in on those when I was trying to help him troubleshoot over the phone.
In your use case, the inverter default configuration with ground relay enabled is probably sufficient so long as you don’t bond in the critical loads panel.
YouTube is a good place to learn amateur-level knowledge from amateurs. I’m not knocking that. It’s a good way to understand at a high-level what’s possible. But understand that most of these guys are in it for the clicks and affiliate income. Of course it’s “easy” they say or you won’t click through the links. And ripping off the lid of a battery and checking if low-temp disconnects work with a little ice water is not testing. The functioning of a BMS is the single most important part of a battery, especially if you use closed-loop communication. Almost all of the “budget” batteries use off-the-shelf BMS’s that all seem to have the same shortcomings. I’m not naming names but I have tried them all. Pylontech and Pytes both make their own BMS’s and have worked with Victron to make for a fully-supported configuration.
Put another way, there is a reason that the retailer that owns EG4 electronics sells both Victron Energy products and Pytes batteries (for example), in addition to their own EG4 brand. I noticed CC is now selling Pytes, too.
I’m sorry to be so preachy, but I don’t want to see you spinning your wheels or asking questions on a forum about something that could have been avoided before you purchase anything.
Now that I’m off my soap box, I looked at your diagram. Why do you have a SmartShunt between the battery and DC buss with batteries that supposedly communicate with the Victron system? Oh wait, it’s because you show a Cerbo-S and not a Cerbo, which has a BMScan communication ports that the Cerbo-S doesn’t.
My suggestion, for what it’s worth: Get a Cerbo GX MKII and better batteries. VenusOS 3.6 fixes any issues with the second CANbus ports. Eliminate the shunt if you use good batteries. You might also consider using a Lynx PowerIn with Class T fuses to bring the batteries to the DC buss. We usually recommend paralleling one pair of batteries together at the terminals and run a set cables from that pair to the DC buss. If you think the three batteries are all you will ever need then just running the one set of cables like you show is fine.
Another alternative is use really cheap 48V batteries (without canbus ports) and use the battery monitor built-in to the Quattros. The built-in battery monitor works just fine in systems that don’t have DC loads and sources other than MPPTs and batteries, such as yours.
I hope this helps. I don’t mean to pee in your cereal bowl. Have a great rest of your weekend!
