The Definitive Guide to Transfer Switch Selection

Product Discussion BLUETTI AC Series
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Hello Bluetti community. I am setting up 2 x AC300’s (split-phase) and 4 x B300’s in a 1000 sqft cabin. The cabin is grid connected but the area tends to lose power more often than I’m comfortable with. The AC300’s will be fed by ~5kw of solar panels, maxing out the 4 PV inputs and 200w panels per B300. Hoping that will be enough coverage for mid-atlantic sun and seasons.

My goal is to rely on grid only when I absolutely have to, with the majority of the circuits covered by the split-phase setup. Critical: most of the lighting, IoT devices, fridge, well pump (240v, 20A), hot water heater (240v, 30A), and possibly the mini-splits (240v, 30A). Minimal use, but at least some coverage as needed. The range, dishwasher, and washer/dryer are out (for now). But capacity sizing is secondary to what my main issue is…

With all that laid out, I can’t tell you how many hours I’ve spent on here, other forums, Google and YouTube trying to determine how to best lay this all out :exploding_head:. My initial plan – which seemed like the obvious approach – was to use the Pro/Tran2 transfer switch for all the critical circuits, switched to the AC300’s full-time, so PV/battery is my primary power source with the option to switch to grid if needed. But after reading all of the nightmare stories of Bluetti customers who doubled as guinea pigs and beta testers and blowing several units along the way, I am unsure of the path forward. From what I’ve gathered, here are some of the known potential issues:

  • AC300’s can error / power off / blow when grid AC power is restored while on the Pro/Tran2. This is apparently due to the floating neutral of the AC300, which is not supported by the Pro/Tran2.
  • AC300’s AC inverter (out) shuts off when grid is restored.
  • Unique considerations are needed for grounding each AC300 member in a 240v split-phase setup (regardless of transfer switch, but compounded by Pro/Tran2).
  • Endless debates around floating vs. bonded neutrals, grounding requirements, potential workarounds, unvalidated theories, etc.
  • Many more, but my head hurts.

Sadly @BLUETTI has provided absolutely no public support or definitive resolution, only 1-off resolutions with a few of you. As much as I love the AC300’s on their own, I’m starting to believe I have made the wrong decision. A fixed hybrid system would have been up and running by now. But here we are.

So, the ask:

Can we get a CONSOLIDATED thread of WORKING setups and definitive information going? I would be most interested in environments that are using transfer switches or other panel workarounds. Can those who have reached a point of stability share diagrams, lessons learned, products chosen, etc.? E.g.

  • are Generac panels the sure way to go? Others?
  • Is there a cable configuration that overcomes some of the issues?
  • Is there a grounding-based fix?
  • Is totally avoiding grid AC input really the right approach?
    …and so on.

Also, can @BLUETTI PLEASE CHIME IN?! For f!%*$ sake. We have spent way too much $$ for premium gear to be in this situation.

BTW, a HUGE thanks to all who have contributed to finding resolutions, spending time with Bluetti engineers, testing unreleased code, and risking their gear/time to get answers. I’m a subscriber to your content. Looking at you @Raymondjram, @t4602yf, @t4602yf, @twister36, and so many others.

Thanks,
Jad

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I also have two AC300 units with six B300 batteries (3 per AC300) and the P030A Fusion Box which is working for me. In my own home, I had installed (as an EE I do everything by myself) in my home a GE 100 A transfer switch to use a 5 kW (20 A) Onan gasoline generator when the utility power went out. I installed the transfer switch right behind the main 100 A panel inside my home, so I diverted the two main 120 VAC lines directly from the utility meter to the switch, then added two new black #4 wires from the switch back to the main panel terminals. I added a white #4 jumper wire from the neutral block in the main panel to the same block in the switch. Finally I added two black #10 wires and a white #10 neutral from the L14-30P generator inlet to the switch. The GE switch only affects the two 120 VAC lines, and the neutral is continuous from the generator to the switch and the main panel, and to the structure ground at the utility meter outside. This was in operation since September 1995 and has not failed or given any problems.

I ordered my Bluetti equipment in September 2021, but due to several manufacturing delays, and later to the transporter shipping, my equipment arrived in Abril 2022. I installed the equipment in a huge Rubbermaid enclosure, and connected the L14-30R on the Fusion Box to the L14-30P generator inlet, effectively replacing the gasoline generator. As power input I added a new 30A 240 VAC circuit through a new 40 A breaker directly connected to the main utility lines inside the transfer switch. I had to fabricate the special 30A cables for the two AC300 inputs since Bluetti did not offer the "Split Phase Charging Cable’ until October 2022.

So as power flows when acting as an UPS, the utility power comes through the new 40 A circuit breaker, then to the AC300 units (and charges the B300 batteries), then the AC300 TT-30 outputs goes through the Fusion Box into the L14-30 inlet toward the transfer switch and finally to the main panels for the entire home. The transfer switch does not switch ahead of the AC300 units but only after them. The transfer switch is used only to switch back to the utility power when I need to do some work on the Bluetti equipment and power it off. The neutral line is also continuous from the AC300 units and Fusion Box to the transfer switch, which is already connected to the main panel and utility meter ground. If the utility power fails, my home sees no interruptions.

In December I installed eight 400 W photovoltaic panels on my home’s roof, and wired them through a homemade distribution and switch box so each AC300 can get up to 1.6 kW of solar power. Since then, I don’t need the utility circuit power to charge and power my home, so that 40 A breaker is kept off, unless I get many cloudy days and the batteries are not charged enough to run the AC300 at night. If you are planning to ask, all of my appliances are “Energy Star”, my electric water heater is set to 20 A at 240 VAC, I don’t have any electric ovens or stoves (I have an induction cooktop that runs at 20 A) and I don’t need my electric clothes dryer, since I have three “Solar Dryers” (three outdoor clothes lines).

This is my layout and my only future plans is to replace the two AC300 with two AC500 so I can run up to 40 A in my home (all of my wires go through EMT and plastic tubing with a ground wire so it can be replaced). The gasoline generator is my ultimate backup if the utility is out and I get little or no Sun to charge the B300 batteries. I just have to manually swap the Fusion Box cable for the generator cable if this happens.

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Anyone else care to share?
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@BLUETTI can you get an engineer to provide some feedback on this? Your documentation still recommends the Reliance 310A Pro/Tran 2 (as discussed HERE), but I would appreciate a response to the concerns and questions presented here. There are still so many unanswered questions, which give me very little confidence in the gear.

Thanks.

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I’m in a similar situation. I’m not doing split phase tho, just one AC300 with some B300 batteries. I bought the Reliance Pro/Tran2 transfer switch AS RECOMMENDED by Bluetti. I am currently installing most of it myself. Once I get a wire ran through my attic, I am hiring an electrician to actually tie in the transfer switch. My original goal was to run all the 110v circuits in my small home. I was going to install a dedicated 30amp circuit tied to the grid to charge the Bluetti when sun wasn’t an option. After hours and hours wasted down this wormhole, I have decided not to worry about the AC charging at the moment. That seems to be where the issues come from (charging via grid AC while still powering the transfer switch). So now I am just going to have the AC300 feed my transfer switch and hopefully I can keep the batteries charged up enough via solar. If not, my intent is to throw the transfer switch back to grid, charge the Bluetti with AC charging until full, unplug the AC charging, then throw the transfer switch back to gen. This is not how they pitched the product at all. But I’m hoping I will be ok with this method. Good luck OP. I feel we are all in this together without the actual support of Bluetti. One thing is for certain, I am not buying anymore Bluetti products from here on out. If I choose to buy more equipment, I am looking at EcoFlow.

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This does not even address the requirement for an AC shutdown switch between the inverter and the Reliance Pro/Tran for single or dual phase installation. Or is a shutdown not required if you are not sending power to the grid?
Thanks.