[willis936]

Returning current through ground is a bad idea in general. You should consider rewiring your house for the safety benefits rather than enabling some smart devices.

Putting significant return current through ground means anything in the environment can be part of the path of least resistance. You will see small voltages across your house depending on what loads are on and there will be load-dependent noise conducted and radiated everywhere. This also puts the system one open circuit away from making nearly every conductive part of your house a shock hazard (if the wrong place in the ground network goes open circuit).

What is done in modern times is to have the current return on a neutral wire then monitor the ground wire for current and open the circuit when current is flowing back through ground (a fault).

[wkat4242]

Huh? I never mentioned ground. I said neutral.

Returning current through ground is impossible in Europe anyway due to residual current breakers. More than 30mA and the whole system shuts down.

And none of the light switches have ground either by the way.

[willis936]

How does the current return? Do you have two phases running to every endpoint?

Try putting a 50 mA fault and see if the GFCI does anything. It won't if you don't have a second line for return current.

[wkat4242]

No, the current goes back through the neutral. This is the normal operating mode with single phase power.

This is different from ground. Neutral is the way the return is meant to go. Ground is a safety feature. Connected to the enclosure in some devices.

So sockets here have 3 wires: Live (Brown), Neutral (Blue) and Ground (Green with Yellow stripe). But the switches only have Live and the Switching wire (Black, the wire that goes to the light). The light then receives the switching wire and has Neutral. Because the power is consumed in the light and returns via neutral.

The switch doesn't need the neutral normally because it doesn't use any power. It just switches it on and off on the way to the light. But the wifi switchboxes do need it because they need to remain connected even when the switch is off.