A PTC Thermistor (POSISTOR®) can be used as a resettable over-current protection device. It has a constant resistance value at room temperature and works as a linear resistor under normal current. When an over-current event occurs, the PTC’s temperature increases due to internal heating, resulting in a very rapid increase in its resistance value. This current limiting protection occurs in several hundreds of milliseconds. Once the current returns to normal, the PTC cools down and its original resistance is restored. POSISTOR® is very effective as a permanently installed resettable current fuse.