Switching device for controlling energy supply of a downstream electric motor

A switching device, comprising:

• a control unit;
• a supply connection;
• a power supply unit;
• and
• a first current path, incorporating a first electro-mechanical switch and, connected in series with the first switch, a circuit incorporating a second electro-mechanical switch in parallel with a semiconductor switch, wherein the control unit is configured to output a switching signal for the first switch, for the second switch and for the semiconductor switch, wherein the supply connection is linked to the power supply unit and the control unit is configured to draw the energy for the switching signals through the power supply unit, wherein the switching device incorporates an energy store and two measurement devices linked to the control unit, wherein the energy store is connected in between the supply connection and the power supply unit, so that an energy supply for the switching device effected through the supply connection is buffered internally within the device by way of the energy store, wherein the control unit is configured to determine by way of the first measurement device any drop in the supply voltage, present at the primary side of the power supply unit, below a first voltage threshold value, wherein the control unit is configured to determine by way of the second measurement device any drop in the supply voltage, present at the secondary side of the power supply unit below a second voltage threshold value, wherein the control unit is designed to evaluate the duration of the time from when the voltage drops below the first voltage threshold value up until when the voltage drops below the second voltage threshold value and emits a signal if the time between the fall below the first voltage threshold value up until the fall below the second threshold value falls below a critical time value.