This circuit interrupts the power supply when grounding is missing. The circuit is from an old documentation (from the 80's) using current transformers and other components of the time.
I found this circuit on a December 1976 Radio Elettronica. The Italian magazine no longer exists, but...
Found in Popular Electronics from the 90s, this circuit uses a 2N2646 and a general-purpose transistor...
Recommended for automotive applications, this circuit was found in an April 1982 Radio Electronics...