The thermal protector is most likely to be used in electric motors of the three-phase type, although only in motors with a Y-connection. Convenience concerns a combination of current and temperature-sensitive protector and reclosing guarantee automatic.
The drawbacks refer to current limitation, because the protector is directly connected to the coil of the single-phase motor and the application is aimed at three-phase motors. After reaching a lower temperature than specified, this protector must be reclosed.
When dealing with phenolic thermal protectors, they are based on bimetallic disks, which have two moving contacts, as well as a resistance and a pair of fixed contacts. The protector is properly driven in series and, due to the thermal dissipation caused by the passage of the chain, a deformation of the disc occurs, causing the contacts to open and the motor supply to stop. FB-810-8
The protectors are bimetallic elements 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.