This is a great picture, but Perilex has L{1,2,3} and N (one blue wire). How come in your picture there are two blue wires near the word Perilex?
Is there also a LAN version of the Sonoff Basic R3, because the housing is metal and potentially no WiFI signal will be able to enter into it.
There are many situations, where the Perilex is used for two phases only. Like a lot of cooking heaters.
No one said, this is the only way to connect it, it’s just an example. 
Not that i know of a LAN Sonoff, but there definitely are switchboards for that.
Just search for Ethernet relay board.
If space and construction allows it, you can mount the Sonoff outside and just bring the wiring inside…
What if I need full perilex switching? Do I then need two of those contactors (and two Sonoffs)?
Yes, I found Relay Pro, which seems super expensive.
The device I wish to control remotely is a Zehnder WHR 930 | Zehnder Group Nederland.
The specifications for the linked contactor do not specify the voltage required for the control signal. How would anyone know whether to send it 0.1V, 10V, or 230V?
If you need to switch all three phases separately, you can do that with a 4way Sonoff:
https://www.amazon.nl/dp/B09BQQ5D4D?ref=myi_title_dp&th=1
You do not need any contactors, the device, you linked, only has ventilators and has very low power consumption (around 100W per phase). The Sonoff will handle that easily.
The question here is: Will the device work, if not all three phases are present? As there is a PCB with some logics in it and the ventilators have more wiring, than power feeding. I can’t say…
Yes, it does, its in its name - 230V
So, the Sonoff Basic R3 also supplies the full 230V?
I am sorry for asking what must be basic questions. I am not sure how to get from my current knowledge state to an EE without visiting a university.
Yes, it does not change the Voltage, it is only a simple switch.
OK, so a true 3-phase motor will actually get the 3-phase ultimately typically from the utility (although one could also create an expensive conversion system with capacitors, I guess (how would such a device be called?)) and a perilex compatible wiring can be created by merely having e.g. a contactor (or just a wire with a couple of other wires coming out of it because it’s a parallel circuit)?
Terms like three phase are mentioned here in relation to using a perilex switch to control mechanical ventilation. There are many uses for perilex, ranging from low voltage switching, via one phase, two groups of one phase, two phase and all the way up to three phase current (which by the way is no longer merely 230V if all phases are combined). It is highly unlikely that the mechanical ventilation is 3-phase. Unless you know what is actually being used here, there seems to be some pretty dangerous guess work going on here.
For a 3phase motor you need 3phase power from the utility.
For a Perilex device mostly only 2 of the three phases are used. It is a way to connect a device with high power demand, which can’t be delivered by a single phase outlet.
Like a cooking device with 2x 2800W of power needed. Single phase 16A can only deliver 3680W.
So the device uses 2 phases to spread it.
But, as the Perilex outlet has 4 connections, it CAN be used for 3phase also.
This is, what I found about the device of Iepton:
It is to complicated to say “yes, you can automate this” easily
From this schematic, there is now way to tell if it is low voltage switching or single phase 230v. Judging from the ground connection and the L1/2/3 designation I’d guess 230V, but my guess could just as easily be wrong. But it could be measured using a multimeter.
EDIT: according to docs it might be 4 wire low current, so there you see how hard this can be to get right.
Also there’s now way to tell what happens if multiple connections are made on the perilex at the same time.
Some hard facts that could be interesting or ignored:
A 16A rated plug can “burn” (in best case only melt) in the same way like a “under 16A” rated plug. 
A 16A rated plug with schuko socket only needs to withstand that 16A for a maximum of 1 hour continuously (schuko specification) 
A common B or C-Type 16A fuse widely used in households will most likely never trip at 16A 
Type Instantaneous tripping current B 3-5 times rated current In For example a 10 A device will trip at 30–50 A C 5 to 10 times In
As we are seemingly talking about balanced HVAC and no heating/cooling I do not expect this to draw anywhere near 10A, let alone 16A.
Also just edited as the docs suggest 4 wire low voltage switching is one of the possible ways to control it, which contradicts my earlier guess of 230V.
I’ve looked up the manual, it maximally draws 320W at full blast
Yes, but maybe not going through the perilex. Docs suggest low voltage 4 wire control is a possibility, that could be the perilex. The diagram shows separate 230V inputs.
If you can confirm though a multimeter that is is not 230 V going through the perilex but maybe say 10v, then you will be able to find ways to control this device through potential free relay switches. If it is 230V it will be trickier because it is unclear if both connections are allowed simultaniously.
