There are various methods of protecting power supplies and electronic equipment from over-temperature conditions. The selection of protection method depends on the sensitivity and complexity of the circuit. In complex circuits, a self-resetting form of protection is typically employed. This enables the circuit to resume operation once the temperature returns to normal levels.

A bi-metallic thermal protector can be considered a resettable thermal fuse. This device disconnects the current at the predetermined temperature and then resets when the temperature returns to normal. The thermal protector is composed of a temperature-sensitive bimetallic strip, which is usually closed during normal operation. As the temperature rises, one of the strips 
expands and bends away from the other, causing the contact to open and disconnecting the circuit. This prevents further heating. Once the temperature decreases, the strips revert to their original position, and current flow resumes.