Because the inductive load will produce back EMF voltage at the moment of power on or power off, the peak value of this voltage is far greater than the voltage that the load AC power supply can bear, it is easy to cause the instantaneous over voltage of the inverter. Therefore, it is very important to use the low-frequency inverter, because the low-frequency inverter has a transformer.

The shunt capacitor beside the switch is to reduce the arc formed between the two contacts of the switch when the switch is off; when the switch is closed, it does not eliminate the effect of electric spark. Because the circuit connected to the switch is often an inductive load. When the inductive load is powered off, the current cannot change suddenly, so it will form an arc between the two broken contacts. On the one hand, the arc will damage the contact (easily burred), and on the other hand, it will affect the circuit breaking time. After adding the capacitor, because the voltage at both ends of the capacitor cannot change suddenly, the contact will be damaged The voltage at both ends of the point can not change suddenly, so there is no spark formation. It can absorb the sharp voltage, protect the contact and disconnect the circuit in time to prevent breakdown.