How Does Thermal Fuse Work?

Thermal Fuse Basics

A thermal fuse is an emergency device used to prevent electrical appliances from overheating. Like an electrical fuse, a thermal fuse completely burn outs when the machine it is attached to gets beyond its safety level. Unlike an electrical fuse, a thermal fuse is melted by excessive heat instead of shorted out by excessive current.

Function

A thermal fuse uses a fusible link--two pieces of metal which are attached together by a substance designed to melt at a particular temperature. Under normal circumstances, current runs through between the two plates, running the appliance. When it gets too hot, however, the fusible alloy--the substance which holds the pieces together--melts, and they spring apart, turning off the current.

The Purpose of a Thermal Fuse

Devices which use heaters, such as coffee machines and hair dryers, have a heating element controlled by a thermostat. The thermostat keeps the heating element at the right temperature by repeatedly turning it on and off. If the thermostat malfunctions and won't turn off, the machine will keep heating up, potentially causing a fire. The thermal fuse stops this from happening by automatically turning off the power if things get dangerously hot.