Hi there,
To kolbep: at the moment the PLC controls lighting only. Timed stairway lights, general on/off, funny stuff like that. It will control irrigation later, once I have budget to install it
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I wonder what kind of grid is at your place Dave. In Belgium most grids are TT, which means the Neutral (star point of the transformer) is directly connected to earth. The mains cable has to be an EXVB (reinforced) cable with 4 wires of minimum 10 mm squared. The earth at the user side is usually one or a set of copper or zink coated pins, or a loop in the foundation. As long as the resistance is below 30 ohm, you are safe to install a 300mA diff. The main earth conductor has to be 16mm squared I believe.
Another big difference I see is that your have a common neutral point and only the fases are interrupted. Over here the neutral and phase need a linked circuit breaker on each circuit. The differential current switch also interrupts all fases and the neutral. Is your main earth conductor connected to this neutral point?
When I hear your electrician talk on the video, the installation seems perfectly safe to me. Ours are over protected and way more expensive, even the basic ones. I am not talking about my semi-industrial stuff.