Overload relays are electrical control devices that are designed to prevent damage to electric motors caused by overloads or current surges. These relays are essential safety devices that protect expensive machinery and ensure the safety of personnel working in close proximity to electric motors. 

The overload relay monitors the current flow to the motor and trips the contactors if the current exceeds a pre-set limit. The overload relay can be adjusted to protect motors of different sizes and can be installed on single-phase and three-phase motors in a variety of applications. 

Overall, overload relays are essential components for maintaining operational efficiency and ensuring the safety of equipment and personnel in industrial settings.