Overload Relays

A thermal relay is a type of relay that protects a motor from overcurrent. It is called "thermal relay" because it operates after detecting a rise in the temperature of the motor coil. In some designs, the terminals are equipped with a cover to improve safety by protecting against electric shocks during maintenance or inspection. Most thermal relays are composed of a heater element and bi-metal section. When current flows through the heater element, the bi-metal section bends and the contacts open. If the relay is activated, eliminate the cause before restarting operation. Types include an automatic type that resets automatically after activation, and a manual type where the user resets the relay by pressing a button after the bi-metal has cooled. Because a thermal relay itself does not have a shut-off function, it is usually used in combination with an electromagnetic contactor.