A self-resetting fuse (PPTC Resettable Fuse), also known as a Polymeric Positive Temperature Coefficient (PPTC) thermistor, is composed of an insulating polymer and highly conductive carbon black particles. Its function is to automatically interrupt the circuit when the current exceeds a safe threshold, preventing damage to wiring and equipment due to overload. After the fault is cleared, it can reset itself without manual intervention.