Use the knife switch or circuit breaker manual control the start and stop of the motor, for example, Figure)

Between the motor and three-phase ac power only knife switch or circuit breaker manual control the start and stop of the motor. Main circuit: from the power supply through protected by electric power plant and electrical appliances directly to the circuit called main circuit of the motor. Features: manual forward control circuit is simple, but the knife switch should not be on load operation. And circuit breaker is a device to cut off the current, also should not be used for the frequent switch load on structure, therefore, start in, stop frequent occasions, use the manual control method is neither convenient nor safe, large labor intensity of operation, to start or stop the motor must to site operation, can't automatically control over long distances. The main circuit of the motor ( Use of knife switch) The main circuit of the motor ( Use of circuit breaker)