Is there a ZigBee “three phase switch” for sale in The Netherlands (apparently, this is a method of switching in which the device being switched interprets the power wave form in a particular fashion as opposed to just on/off which also works in HomeAssistant?
Sometimes three phases are also used for high power devices; this is not such a device.
I do live in the Netherlands, I’m a electrician, but I still have difficulties to understand, what you are looking for…
What device are you going to manage with this switch?
A heat recovery installation.
Something like this?
Yes, the turn switch with multiple states is what we have now, but people are too lazy to manually control it, so we need a Zigbee version.
There are many examples of people using double relays or double switches, though admittedly mostly z-wave or wifi (I do not now any zigbee equivalent) to automate the switch you describe. But in general it is not wise to blindly adopt a solution without knowing exactly wat is behind it. Is is switching 230V or low voltage, do you intend to keep the original switch and automatie it at the same time, does the appliance allow channels on simultaneously or not…
I have an Itoh mechanical ventilation attached to it that switches on 230V and does not care if multiple channels are switched on. I automated that using a Fibaro double switch, keeping the original switch in the kitchen connect to the switch inputs of the Fibaro. I made sort of an extension cord that I can put inbetween the Perilex connection at the site of the mechanical ventilation, so I can remove it as easily as I put it in between.
I would not advise venturing in such an operation without knowledge of electrical installations. For the same reason I do not think there will ever be an easy to use out of the box solution. This kind of switch is used in too many different situations.
Just assume whatever is standard and according to regulations is connected to it. I don´t think there are many options in that case. I think the control is low voltage, because that´s just sane electrical design. If you don´t need high power near people, don´t use it. I’d hope/expect that’s somewhere in the building code.
This isn’t some research project.
There is state 0,1,2 (and possibly also 3) on a low voltage circuit. How hard can it possibly be? Disconnect power, disconenct existing 3 wires, reconnect, pair via Zigbee and done.
If existing products are any more difficult than that capitalism is broken, because there are tens of millions of such setups in the world. We already have two.
Yes, it second this.
There is no really a smart direct replace unit for this.
It could be made, with the solution from Edwin, or with a Shelly like this:
But as said. You really need to know exactly, what you are doing and program it the right way. Other ways you could get a nice sparky show and talk to some real firefighters 
Well, if you assume low voltage and it is 230V as it is in my case (because that is how older mechanical ventilations used to be wired) then you fry the switch. If it is indeed a low voltage box and you put 230V on the wrong connections then you fry the ventilation box. Assumptions are dangerous here, that was my whole point.
If it is low voltage, you can get away with this:
I will obviously check the schematics again before I actually buy something. Frying a device is cheaper than not doing anything. If we think it’s too complicated, we can arrange an electrician (which is probably cheaper than doing it myself anyway).
I would prefer to have one with physical switches too such that when Home Assistant is offline for whatever reason it still works.
… and convince the insurance people they need to pay the bill regardless…
Sonoff also appears to be some worthless cloud thing. I hate other people’s computers, because they always mess up.
That Shelly thing is hugely overdimensioned (only 130W is used by the device).
If it is esp32 based (I think it is) you can flash EspHome or tasmota on it and be free of the vendor or cloud.
I’d prefer to give my money directly to people providing a useful product to the economy.
The form factor of the Shelly is also completely wrong. The Shelly could be used for measuring power usage of a couple of AC units as it has a DIN rail, but otherwise it looks in no way like the current tri-state manual control there is now.
If 130W spec is enough depends on the type of the load (capacitive/resistive/inductive). Since it is powering an electric motor, over dimensioning is probably wise. And if it is switching low voltage as you think, 130W is not likely delivered over low voltage. But it is ok to switch 10V with a relay that can handle 230V/130W. It all depends on the type of device connected. Again, knowledge of electrical systems is not optional.
If you want to keep the original switch, the form factor is moot as you will not be able to put it in the same wallbox as the switch. The HA operated switch goes somewhere near the ventilation unit, which is probably connected with a perilex plug. That is where I put the extension cord with the switch inbetween.
The way it works is that the Home assistant controlled switch will overrule the mechanical switch, until the moment you change the mechanical switch and then Home assistant will take the cue from the mechanical switch. Until Home assistant decided to overrule again…
If you do not know what you are switching, you need at least two potential free relay switches that are able to handle 230V/200W. If you do not know if it is safe to have them both on at the same time, it is probably wise to create a more complex circuit, which probably involves more relays. I would advise against solely relying on good programming. If you want to keep the old switch the device must have mechanical switch inputs to control it, so you can attach the old switch to it.
The sonoff seems to fit that description perfectly.
Without a diagram, I find this impossible to understand. I also have the impression that you are using a lot of unnecessary jargon.
The form factor is not moot, because that DIN rail mounted device has a terrible interface (they are not physical buttons, if they have buttons at all).
The device is not intended to have buttons of its own. You’ll be using the original switch in the wall and Home Assistant. All it needs is places to attach wires.
So if you can not understand most of the things I wrote, I am sorry but in that case I won’t be the one to draw you the diagram. I don’t want to be responsible for it being used the wrong way. If you intend to involve an electrician then I won’t need to, because he/she will be able to draw one up easily.
EDIT: seeing you live in the Neterlands - the thread in Dutch describes all kinds of ways to do what you want in different sitiations. If you can make sense of the one you need, the diagrams are there. But I do not accept any responsibility:
https://gathering.tweakers.net/forum/list_messages/1925132