1. Interrupt the power supply when over-current occurs on downstream devices 2. Do not start and stop the AC drive frequently by switching the contactor on and off (less than twice per minute) or use it to directly start the AC drive. 3. Eliminate the higher harmonics of the input side effectively and prevent other devices from being damaged due to distortion of the voltage waveform. Eliminate the input current unbalance due to unbalance between the power phases. 4. Reduce the external conduction and radiation interference of the AC drive. Decrease the conduction interference flowing from the power end to the AC drive and improve the anti interference capacity of the AC drive. 5. Improve the power factor of the input side. Improve the efficiency and thermal stability of the AC drive .Eliminate the impact of higher harmonics of the AC drive input side and reduce the external conduction and radiation interference. 6. The output side of the AC drive generally has much higher harmonics. When the motor is far from the AC drive, there is much distributed capacitance in the circuit and certain harmonics may cause resonance in the circuit, bringing about the two impacts: 1)Degrade the motor insulation performance and damage the motor in the long run. 2)Generate large leakage current and cause frequent AC drive protection trips. If the distance between the AC drive and the motor is greater than 100 m, install an AC output reactor.