The thermal protector has a great possibility of application, and in most of them it is done in motors of the three-phase type, however, only in motors with Y connection. The advantages are combination of current and temperature sensitive protector and possibility of automatic reclosing . The disadvantages are the current limitation, because the protector is connected directly to the coil of the single-phase motor and the application is aimed at three-phase motors. After a lower than specified temperature has been reached, this protector must be reconnected. Due to this reclosing, two types of protectors can be obtained: the protector with automatic reclosing and the protector with manual reclosing.
The phenolic thermal protector refers to a bimetallic disk, which has two moving contacts, a resistance and a pair of fixed contacts. The protector is properly driven in series and, through the thermal dissipation caused by the passage of the current, a deformation of the disc occurs, causing the contacts to open and the motor supply to stop. These protectors consist of bimetallic components that have normally closed contacts, used in single-phase induction motors, in order to avoid overheating caused by overloads, causing the rotor to lock, as well as voltage drops.