Hi
I need to be able to switch my home between grid and off grid and this requires an air-gap transfer switch. I want to make this transfer smart and dependent on entity values. I have found some smart transfer switches but I get crickets when I ask if they can work with HA. I have found some that work with EWeLink and Tuya but given my experiences trying to use eWeLink and tuya based entity values I am not going down that integration path. Can someone suggest an air-gapped smart transfer switch?
Thanks
Michael
Can this even be allowed by local code/regulations? 
Post what you found. Are they motor or contactor based? Certified? Flashing the “smart” chip with esphome or replacing it with esp32 could be one option.
Depending on location, yes. We’re in an area where automated power transfer is permitted by virtue of the fact that it’s not explicitly prohibited, and no particular method of how to accomplish it is specified. Essentially, as long as going from one power source to the other won’t cause problems for a grid-tied generating utility, pretty much any method is fair game around here.
We’re in a rural location, though. Go about 14 miles West of here and it’s a very different story: residential permitting for automated power transfer turns into a bureaucratic nightmare very quickly unless you have a person in the home who is dependent on around-the-clock use of mains-powered medical equipment. Even businesses are given a hard time unless they’re directly supporting first responder, medical, or critical distribution and retail (e.g., food and/or medication) needs.
You can install a 200 amp DPDT contactor as your grid transfer. I would oversize it, but you don’t have to. Then you control the contactor with a Shelly device.
That said, you have to think about the power fail problem. Let’s say you are on utility power and it fails. Now the Shelly, and the 12 volt power that controls the contactor and the HA server are all not powered. How can you command the transfer switch to your backup? The best (only?) way to do this is to wire the transfer switch to “default” to backup when power is removed from the control coil.
Read the NEC (assuming you are in the US and NEC applies) and you find that “ATS” (automatic transfer switch) is legal. But I’d bet $1 that your local utility will not connect power to your house unless there is an obvious MANUAL switch that will disconnect your house from their utility power. You will need to have BOTH.
You need to follow the code, but the utility company will likely require more than just basic code. They have authority to even tell you where the switch must be located and what words you must write on the label. The reason is that the utility company needs a way to VISUALLY determine the switch setting by looking at a physical device.
Not only does the switch need to be able to be visualy verified, the power company will likey requre that thhere handle by “lockable” so a lineman can pllace a padlock on the handle. The power company will explain thir requiremts (which will be MUCH more strict then the NEC). But AFTER this switch the wires are yours and only the NEC and the city inspector’s opinion applies
But you can always place your ATS in series with the mechanical disconect switch the power company will require.
What the power company is concerned about is that your house might backfeed their wire and make it “hot” when a lineman disconnects it. They are rightly concerned about their employees’ safety.
Why should we assume that?
What’s amusing is that I grew up in one of the countries that started a conversion to the metric system back in the '80s, then emigrated to the US about three-quarters of the way through it. Every time I visit family outside of the country it’s natural for me to just slot into using the metric system without thinking about it, but having had the conversions drilled into my head at an impressionable young age it’s not surprising. About the only practical impact on my day-to-day life of living somewhere where SI units are optional at best is that it makes obtaining metric drill bits locally somewhat of a pain, but mail-ordering generally resolves that issue.
Interestingly, the US is actually a metric country, and has been since the 1870s or so - SI units are completely legal for day-to-day usage, privately or in business, and the US was one of the countries to originally sign the Treaty of the Metre. Even US Standard units (calling them ‘Imperial’ in this context would be incorrect) are legally-defined in metric terms, so if one really wanted to stretch things a bit it could be claimed that the inch is really just another way of saying ‘25.4mm’.
What’s the difference between a US and an Imperial gallon? About 750ml 