The TMOV™ is constructed with a conventional MOV ceramic disc and a thermal cutoff device inside the same housing. Sometimes a conventional MOV will be exposed to an energy level that is beyond its capabilities. Or sometimes an MOV has reached the end of its useful life and just shorts out. Either of these conditions can result in rapid burning or fragmentation. It is important to disconnect the MOV from the circuit as quickly as possible to lessen the chance of serious damage. TMOV response time is ultra fast because the thermal cutoff component is mounted inside the part on the ceramic disc itself. This is still not a 100% solution to MOV destruction, however. There is always the possibility of a very large transient coming in that can destroy even a TMOV. This is just another level of insurance against the possibility of physical damage.