Multifuse® PPTC devices can exhibit this PTC effect because of their unique construction. These devices are made from a conductive polymer. As users know, polymers are insulative materials, but Bourns mixes carbon into the polymer matrix which brings highly conductive properties to the polymer. It is the carbon that allows current to conduct through the device and hence, the Multifuse® PPTC device is low resistance in its normal state. However, if the device witnesses an overcurrent surge, the Multifuse® Polymer PTC will heat at the rate of I2R. This heating causes the device to change phase from low resistance to high resistance as the carbon chains start to separate. The PPTC device will stay in the high resistive state as long as there is a fault. Once this fault is removed and the power has been cycled, the PPTC device will return to the low resistive state.