You mention it is a thermal relay. So it it probably operates based on some
temperature criteria. Most common is if something exceeds a set temp trip
value that device or circuit is shut off.
But to Klaus's point read the instrument or machine manual for better
insight into its operation.
A relay that opens or closes contacts with a bending mechanism as a result of the difference in the expansion coefficients of a bimetal, which is heated by the current. ... The thermal relay is combined with a magnetic contactor because it cannot switch the main circuit by itself. The operating point can be changed.
Role of Thermal Relay?
Thermal overload relays are economic electromechanical protection devices for the main circuit. They offer reliable protection for motors in the event of overload or phase failure.