A relay switch (SW) in an AC main line has a DC-powered amplifier (AMP) for applying amplifier control sensor signals to the control circuit of the relay switch.

An automatic regulation keeps constant the starting current during the starting time of the switching contactor.

If this is not the case at one moment in time, the protective motor switch (Q1) is triggered and the motor drive is brought to a stand still.

Electronic driving components sized to drive switching contactors of a determined power class are generally used.

In certain cases a triggered switching device (1), e.g., a contactor, must remain in is ON position even if the power supply is cut off.

The new circuit has a control circuit (34), in which a switching element (2) and a measurement resistance (3) are connected in series to the contactor coil (1).