the operating current may be above the holding current of the PPTC. The device may not return to its original resistance value; it will most likely stabilize at a significantly higher resistance (up to 4 times initial value). It could take hours, days, weeks or even years for the device to return to a resistance value similar to its original value, if at all. A PPTC device has a current rating and a voltage rating. Applications These devices are often used in computer power supplies, largely due to the PC 97 standard (which recommends a sealed PC that the user never has to open), and in aerospace/nuclear applications where replacement is difficult. Another application for such devices is protecting audio loudspeakers, particularly tweeters, from damage when over driven: by putting a resistor or light bulb in parallel with the PPTC device it is possible to design a circuit that limits total current through the tweeter to a safe value instead of cutting it off, allowing the speaker to continue operating without damage when the amplifier is delivering more power than the tweeter could tolerate. While a fuse could also offer similar protection, if the fuse is blown, the tweeter cannot operate until the fuse is replaced. See also Positive temperature coefficient References Over-current protection devices Resistive components