This grounding test circuit was found in an American 80's documentation. The circuit is for the 110 V power grid but can be changed to the 220 V power grid.
This control panel allows the use of NO and NC sensors, turning the alarm on after 30 seconds...
This LM139, 239, or 339 comparator configuration appears elsewhere in this site and this section....
The frequency of the blinking of this circuit is given by the capacitor that can have its value...