LVP Controller Operation:
1. Push the START button that energizes contactor coil M, closing the M and Ma contacts. When START button is released then the circuit will remain finished, since the Ma contact remains closed and shunting the open begin switch.
2. Whenever a low voltage condition occurs then the M coil will drop out at a few pre-determined value of voltage, and the M and Ma contacts would open. The START button has to then be pushed to restart the motor.
Figure: LVR Controller
3. Depressing the STOP button deenergizes the M coil that then opens the M and Ma contacts.
The aim of the LVR controller is to de-energize the motor in a low voltage condition and restart the motor while normal voltage is restored. That category of controller which is describing in above figure is used primarily on small and/or critical loads example for cooling water pumps needed for safety-associated equipment.