Any rapid rise in temperature will open the thermal link which will permanently disconnect the MOV from the circuit. Thermal runaway, with all of its dangers, is eliminated by this action and is no longer a threat. When the thermal fuse opens, current will instantly fall to zero and the temperature will begin to decrease as shown in the graph. Once the thermal fuse opens, it will never close again and reestablish current flow. The TMOV is a one-time-acting device similar to a conventional overcurrent fuse.