The Q1, Q2, Q3 contactors must be chosen according with rated power of your motor. Basic circuit - figure 1 There are Stop, Forward and Reverse buttons, two low current double pole double throw relays for the control circuit (thin wire lines) and the power circuit (thick wire lines) which uses a double pole single throw relay (RMAIN) and a double pole double throw relay (RDIR). When overload occur circuit breaker opens Q1 so the motor is stopped. 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. This could be used for changing the direction of a m. By pressing Forward push button the Q2 coil contactor is energized the motor will be connected for clockwise run and maintains itself after the button Reverse by means of auxiliary switch Q2, the Stop button and the auxiliary contact of Q3, which serves as interlock, thus avoiding simultaneous connection of Q2 and Q3 contactors. In this video I show how to use a Double Pole Double Throw (DPDT) switch or relay as a polarity changer. 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. Motor protection with MCB with thermal and magnetic trips
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