MOV（Metal Oxide Varistors）is a kind of surge device with voltage limiting, and sensitive to voltage change. At present, the varistor used for surge protection of low voltage electrical appliance is a varistor with zinc oxide as the main material and doped with a variety of metal oxides. MOV is polycrystalline semiconductor ceramic components made by typical electronic ceramic technology.

MOV has a symmetrical volt-ampere characteristic curve, and the current flowing through the MOV increases exponentially with the increase of the voltage at both ends of the MOV. When applied, MOV is generally connected in parallel in the circuit. When the circuit works normally, it is in a high resistance state, which does not affect the normal operation of the circuit. When abnormal transient overvoltage occurs in the circuit and reaches its conduction voltage, MOV rapidly changes from high resistance state to low resistance state, releases the instantaneous overcurrent caused by abnormal instantaneous overvoltage, and clamps the abnormal transient overvoltage within a safe level, thus to protect the subsequent circuit from abnormal instantaneous overvoltage damage. MOV has high instantaneous pulse absorption capacity and large capacitance, which is generally used for lightning protection at AC input end. Because the surge absorption capacity of MOV depends on their physical size, different transient surge current values can be obtained by customizing MOV of different sizes.