A thermal cutoff is a safety device for electrical equipment. It ceases the flow of current in a device when heated to a specific temperature. These devices can be reset either automatically or even manually.

Thermal fuse

Thermal fuse is a cutoff that utilizes a fusible link (applicable for only one time). The thermal fuse is not like the thermal switch that gets reset automatically whenever there are temperature drops. On the contrary, it's like an electrical fuse – a one-time-use device that cannot reset itself and needs to be replaced when it is triggered. Thermal fuse is generally used in those situations where overheating is a rare occurrence.

One component is a little meltable pellet that holds down a spring. The spring gets released when the pellet melts completely. As a consequence of this, the circuit breaks up. The NEC Sefuse SF series, Tamura LE series, Hosho Elmwood D series and Microtemp G4A series may manufacture the alloy pellets containing silver, copper, and beryllium to melt at a precise temperature.

Thermal fuses have found its use in heating electrical appliances like hairdryers and coffeemakers. It serves as a safety equipment to cease the flow of current to the device in case of any malfunction that would result in the temperature to ascend to risky levels, potentially lighting a fire. Thermal fuses react only in case of excessive temperature and not during the flow of excess current. This is one of the main differences of the device with a normal electrical fuse. 

Thermal Switch

A thermal switch popularly known as a Thermal Cutout (TCO) or thermal reset is an electrical equipment that opens with a "plink" sound at a higher temperature and closes itself automatically when there is a drop in temperature. The thermal switch is a bimetallic strip that is often encased in a cylindrical glass bulb to shield it from short circuits or dust particles. Another basic configuration utilizes a bimetallic shallow dome-shaped top which "clicks" to an inside out inverted cap when warmed, for example, the "Klixon" brand of thermal cutouts.

The thermal switch can be reused. Thus it is used in temporary places that are user-correctable. Thermal switches are used as thermostats in some cooling and heating system. It is also used in power supplies in case of any malfunction (overload). Another category of thermal switch is the Positive Temperature Coefficient thermistor (PTC). These kinds of thermistors have a “switch” temperature. At this temperature, the resistance rises rapidly and limits the current in the circuit. It is used in motor overheat protection.

Thermal switch is also used in some luminaire, particularly with downlight, where unnecessary heating is well on the way to happen. This might sometime result in "cycling". It is the process where the lights turn on and off after every few minutes. Glimmering radiant Christmas lights take advantage of this impact.

This was all we have about Thermal Cutoffs. Brands that manufacture this equipment are TE Connectivity, Littelfuse and Bourns. Make sure to refer them using the links as provided. Hope you liked the article and Thank you for reading.

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