Thermal overload relays are installed to protect the motor in case of phase failure or overload. The thermal overload relay does not directly shut down the load. Instead, it triggers one or several auxiliary contacts which then disconnect the motor. Most thermal overload relays can be mounted directly to the contactor. Thermal overload relays have three pins. They contain a thermal release - hence the name - usually a bimetal element. Direct or indirect heating caused by overload bends the bimetal release and the relay trips.