Simple and cheap overload protection for multiple secondary taps of a transformer
I worked with PTC resettable fuses for many years. They act quickly but do need 15 to 30 seconds or so to cool off enough to conduct current again-it depends on its mass. Their worst enemy is being in a circuit that can source enough voltage to arc internally and destroy the PTC fuse.

The second issue is that it is important to know for certain the highest sustained current to be consumed, compared to a gross over current that would damage a device or the transformer. This helps make sure the PTC fuse will survive an overload yet also reset when the current drops to a safe level.

They cannot be used where high surge currents or high voltage spikes are the norm. Use MOV's to clamp down any chance of voltage spikes do to back-EMF. Use in-line fuses if there is a chance of surge currents much greater than the expected maximum current, which may originate from a charged capacitor or intense back-EMF from a high value inductor.

When shopping for PTC fuses pay close attention to the spec sheet, and you will be able to count on them as expected.