The Sensata Dominican REP (or Mexico depending on where made) RP1B is a thermal protector* for lighting fixtures. It has a dedicated voltage of 120Vac and has low sensitivity. It has three leads, black, white, and blue. When the temperature of the fixture is exceeded it will cause the light to blink. It is auto resetting for when the fault is corrected. The Sensata RP1B is designed to fit into a 1/2" KO.
The black lead wire is always connected to the input live wire The white wire is the common which is permanently connected at the factory with an extra six inch piece of wire of the same color The third wire of the RP is permanently connected to the live side of the load
*A thermal protector is a safety device designed to prevent lighting fixtures from overheating, which can lead to damage, fire hazards, and reduced lifespan of the fixture.