Motor protection with MCB with thermal and magnetic trips
Operating mode: Same as for direct on line starting instead of fuses and thermal relay you can use a motor circuit breaker with thermal and magnetic trips, a simple but at least as effective component. By pressing Forward push button the Q2 coil contactor is energized the motor will be connected for clockwise run and maintains itself by means of auxiliary contact of Q2, Stop, Emergency stop buttons and the auxiliary contact of Q3, which serves as interlock, thus avoiding simultaneous connection of Q2 and Q3 contactors. In a similar manner things take place if we want to change the direction of rotation, thereby pressing Reverse button contactor Q3 is connected so the motor is rotating counterclockwise, this is possible only by activating previously the Stop button. When overload occur circuit breaker opens Q1 so the motor is stopped. Special attention must be taken when connecting capacitor and motor coils.
MCB and contactor calculation
The values for Q1, Q2, Q3 must be chosen according to the rated power of your motor, base on the data found on motor plate. Fuse F1 for the control circuit may be up to 10 A.