This Sonoff basic had burned because all the current is passing trough the sonoff cause of the neutral wiring.
You should have to wire the two power wires outside the sonoff ! And only wiring the pilot line inside the sonoff.
If all your heaters are wired in this way, I think you must modify all wiring and take out the neutral power line.
@Axh3ll I’m not an expert but if you have a look below to the burned sonoff with my wiring I’m not sure I can do better without other alimentation and no pilot wire from wall. As you can see the line is plugged directly to the heater, it “should have been safe”.
Imo the faulty component was the 1n4007.
I’m sorry but what goes in goes out ! If you drain for example 10amps trough the line wire they comes back trough the neutral wire + the sonoff and the pilote consommation
As I understand it, you are splitting the line/live on input to the SOnOff, one runs past the SOnOff and provides the heater with it’s main power line/live. The SOnOff is not involved in this line/live current.
You use the SOnOff to send a control signal to the live return of the electrical heater which tells it to be on or off.
However, @Axh3ll is correctly pointing out that you do not split the neutral in the same way. So all the current the electric fire is consuming via the separate live/line is coming back on the neutral wire, through the SOnOff which is not rated for this task.
It is a common miss conception that neutral wires are somehow safe. They are no different to live wires once in an active circuit. Kirchhoff current law states that the current will be equal at all points in a circuit. In fact when we label a wire “line” or “neutral” is only relative and pretty much arbitrary as to what point a line becomes a neutral. If you were measuring current in a circuit you could not tell from measurements alone which was the live and which was the neutral.
If you have more of these or other things wired this way I would revise them. Split BOTH the live and neutral through Wago’s, not just the live. Create two completely different parallel circuits. One high current, one switch/signal current. Put a very small fuse, like 250mA on the switch line to be sure you don’t get surprises due to failures or shorts.
In fact, I suspect there is a very high probability, if it’s anything like boilers etc., that the wall heater has a switch live out and live return for the pilot control. Just power the wall heater from an outlet and put the SOnOff on that pilot line supplied by the heater, you may then borrow a neutral from anywhere you want. Your SOnOff will have only 1 wire leaving it. Some devices might not like powering the SOnOff from it’s live switch wire, they can have very small value fuses as the switching wire is designed to carry virtually no current, often called (rather incorrectly) “Volt less”. In this case you go back to how I suggested above, two parallel circuits with the SOnOff ONLY switching the pilot wire and the main 16A flow coming nowhere near it.
To be more sure, don’t use a SOnOff Basic. Use a smart switch that is NOT pass through, but simply closes the circuit on the pilot wire and is powered independently. SOnOff variants like this exist as well, I believe the Shelby’s.
I could propose a safety feature that the SOnOff should switch both the live and neutral to prevent this kind of mistake, but as it would incur costs and other issues doing so, it’s unlikely. So a non-passthrough, isolated relay controller would preferential.