Thermal fuses and thermal switches are two different types of thermal cutoffs. They are devices which will interrupt an electrical current when heated to a certain temperature. They are used inside electrical appliances to control temperature of the appliance.
So what’s the difference between them?
The main difference between these two types of thermal protectors is that the thermal cutoff is reusable, and the thermal fuse is not. If a thermal fuse gets triggered when an electrical appliance reaches a hot enough temperature, the fuse cannot be reset. It must be replaced. A thermal switch, however, will open when a device reaches a certain temperature, and then close again when the temperature drops.
When do you use each of them?
It might be easier to explain the difference between these two devices by explaining where and when to use thermal fuses and thermal switches. Thermal fuses are used in devices like hair dryers, toasters, coffee makers, microwaves, and many more. If any of these devices reaches a temperature which is two hot, the thermal fuse will be triggered, automatically shutting off the device. It is a safety mechanism which prevents appliances from overheating. Pretty much every home has devices which use thermal fuses. But to trigger a thermal fuse is a rare event.
Thermal switches, on the other hand, are in devices which frequently need to have their temperature controlled. One example is a thermostats. The thermal switch turns off the device when it gets to a certain temperature, and then turn it back on when the temperature drops again. Thermal switches might also be in some light fixtures which are likely to overheat. Flashing Christmas lights, for example, a controlled by thermal switches.
How do they work?
There are many different types of thermal fuses. A common one uses a spring held down by a small meltable pellet. When the device becomes so hot that the pellet melts, the spring will be triggered, shutting the device off.
There are also many different designs of thermal switches. One design example is a bimetallic dome-shaped cap which inverts when heated, and then goes back to its normal position when the temperature drops.