This slide shows how temperature affects an MOV. As can be seen, most of the change in the current occurs at the low “leakage” end of the V/I curve. As the current increases, the dependence upon temperature is much less pronounced and is usually neglected up to the maximum temperature allowed for a particular MOV family. All of the available datasheets contain derating information for operation at elevated temperatures. Keep in mind that an MOV is not intended for voltage regulation where there is a continuous DC current flow. MOVs are designed to protect downstream circuitry from the occasional overvoltage transient event which lasts no more than a millisecond or two. The average continuous power that can be handled by an MOV is normally less than 1W, but the transient power is thousands of Watts.