Method and safety device for ground fault circuit

Method for the protection against leakage currents generated in the supply of a load (16) connected to an electrical network (10), comprising the phases of:

• (i) obtaining a zero-reference value by acquiring one or more times a signal (90u) proportional to the leakage current without generating test leakage currents;
• (ii) generating a test leakage current and acquiring a corresponding signal (90u) proportional thereto as test-value;
• (iii) detecting the actual leakage currents and generating a signal (90u) proportional thereto;
• (iv) acquiring a signal (90u) proportional to the actual leakage currents and disconnecting the load (16) from the electrical network (10) when reaching a dangerous condition corresponding to an acquired signal (90u) of a magnitude greater than a limit value.

Apparatus (1) for performing the method according the preceding claims, comprising

• an electrically controlled switch (20) set between the network (10) and the load (16), which disconnects the load (16) from the network (10) when open and connects it when closed;
• detecting means (30) for leakage currents that generate a signal proportional to the same leakage currents;
• a generator circuit (40) able to generate a test leakage current,
• an elaboration unit (50) connected with the detecting means (30) to acquire said proportional signal, with the generator circuit (40) for the control thereof, and with the switch (20) to drive its opening with a control signal (38) whenever a dangerous condition is met;
• characterized in that the elaboration unit (50) is adapted to perform at start-up an acquisition of a zero-reference value by reading the detecting means (30) without generating test leakage currents, to generate a test leakage current by driving the generator circuit (40) and to acquire a corresponding signal (90u) proportional thereto as test-value;
• then the elaboration unit (50) is further adapted to acquire a signal (90u) proportional to the actual leakage currents and to disconnect the load (16) from the electrical network (10) when reaching a dangerous condition corresponding to an acquired signal (90u) of a magnitude greater than a limit value.