The Sensata Dominican REP (or Mexico depending on where made) RP15A is a thermal protector* for lighting fixtures. It has a dedicated voltage 208Vac. The RP15A has high sensitivity and has four leads, black, white, blue and yellow. 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 RP15A 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 all common wires The yellow wire of the RP-15A is connected to the 208 Volt tap of the ballast The blue wire is then connected to the tap of the ballast which will match the input voltage Although the primary usage is 120/277V, the thermal protector inside of these units is rated up to 480 VAc
*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.