Thermal cutoff

[2] Another mechanism is more similar to an electrical fuse, a fusible element that melts when subjected to temperature above its threshold.

The elements are conductive and usually consist of binary or ternary fusible alloy of tin, bismuth, antimony, indium, lead, and other metals.

They function as safety devices to disconnect the current to the heating element in case of a malfunction (such as a defective thermostat) that would otherwise allow the temperature to rise to dangerous levels, possibly starting a fire.

The thermal switch may be a bimetallic strip, often encased in a tubular glass bulb to protect it from dust or short circuit.

Thermal switches are used in power supplies in case of overload, and also as thermostats, and overheat protection in some heating and cooling systems.

Thermal switches on microprocessors often stop only the fetching of instructions to execute, reducing the clock rate to zero until a lower temperature is reached, while maintaining power to the cache to prevent data loss (although a second switch, with a higher triggering temperature, usually turns off even the cache and forces the computer to reboot).

This type is used when an automatic and unattended restart would create a hazardous condition, such as sudden startup of a powerful motor without warning.