PURPOSE: To prevent the burning of capacitors by connecting resistances and switch parts between the terminal of an induction motor and the capacitor and opening the switch means of the switch part by being linked with the opening of a switch.

CONSTITUTION: The induction motor 8 is connected to the U, V and W phases of power sources through wiring breakers 1, first electromagnetic switches 2 and thermal relays 3. The switch parts 11 for preventing the self excitation of the motor which consist of second electromagnetic switches 9 and the resistances 10 by connecting them in parallel between the respective thermal relays 3 and the respective R, S, T terminals of the induction motor(IM) 8. The phase advance capacitors 6 for improving a power factor are connected to the self excitation preventing circuits 11. The capacity of the capacitors 6 is set to be that which requires the power factor. When the guide electric motor 8 stops, the first electromagnetic switches 2 and the second electromagnetic switches 9 are interlockingly opened and the self excitation of the motor 8 can be prevented through the resistances 10.