An overload relay is designed to protect an AC motor from overheating by monitoring the current flowing to the motor. If the current exceeds the amperage set point for a specific period of time, the relay trips and sends a signal to turn the motor off. IEC overload relays are most often used by machine builders for a cost effective solution for motor-starting applications. IEC overload relays can be either bi-metallic or solid state in design and have Class 10 or Class 20 trip curves.