If a polyswitch fails, and if there are no faults downstream of the device, it can be substituted with a fuse or a wire link. A replacement polyswitch can often be found on old motherboards -- they are used to protect USB or PS2 ports.
miniSMDC125F/16, 1.25Amp, PolySwitch, Raychem Circuit Protection:
http://www1.futureelectronics.com/doc/R ... __16-2.pdf
http://www.anglia.com/raychem/datasheets/187_216.pdf
PolySwitch Resettable Devices, Raychem Circuit Protection:
http://www.datasheetarchive.com/indexdl ... 070002.pdf
https://en.wikipedia.org/wiki/Resettable_fuse
PTC fuses reach a high resistance with a low holding current under fault conditions and cycle back to a conductive state after the current is removed, acting more like circuit breakers, allowing the circuit to function again without opening the chassis or replacing anything. A PPTC device has a current rating and a voltage rating. When the current flowing through the device (which has a small resistance in the on state) exceeds the current limit, the PPTC device warms up above a threshold temperature and the electrical resistance of the PPTC device suddenly increases several orders of magnitude to a "tripped" state where the resistance will typically be hundreds or thousands of ohms.
When power is removed, the heating due to the holding current will stop and the PPTC device will cool. As the device cools, it regains its original crystalline structure and returns to a low resistance state where it can hold the current as specified for the device. This cooling usually takes a few seconds, though a tripped device will retain a slightly higher resistance for hours, slowly approaching the initial resistance value.
The following example is from a Samsung HD400LJ drive:
