Shown here is the TMOV design schematic circuit. Littelfuse’s TMOVs are metal oxide varistors with an integrated thermally activated element. The thermal element is designed to open when the overheating occurs due to abnormal overvoltage or MOV EOL. This is the reason why this kind of MOV is called a thermally protected MOV or TMOV. Littelfuse also offers the iTMOV. The “i” denotes indication, as this additional 3rd wire lead can be connected to a monitoring circuit which can indicate the TMOV replacement is needed.