As industrial and domestic electricity loads continue to increase, more and more electrical equipment will have problems such as overcurrent and overheating during operation. If measures cannot be taken in time to protect them, it will have serious influence for personal safety and the integrity of the equipment. In order to avoid this situation, people began to widely use overcurrent and overthermal protectors. As one of the representative products, the HCET-A series overcurrent and overthermal protectors have also attracted much attention for their principles, functions and applications.