The 3RU21 thermal overload relays up to 40 A have been designed for inverse time delayed protection of loads with normal starting against excessive temperature rises due to overload or phase failure. An overload or phase failure results in an increase of the motor current beyond the set rated motor current. Via heating elements, this current rise heats up the bimetal strips inside the device which then bend and as a result trigger the auxiliary contacts by means of a tripping mechanism. The auxiliary contacts then switch off the load by means of a contactor. The break time depends on the ratio between the tripping current and current setting Ie and is stored in the form of a long term stable tripping characteristic. The \"tripped\" status is signaled by means of a switch position indicator. Resetting takes place either manually or automatically after a recovery time has elapsed. Siemens SIRIUS Thermal Overload Relay, 50/60 Hz Frequency, 1NC-1NO Contact Form, 28 A at 690 VAC Contact, 3 Pole, Contactor Mounting, Threaded Terminal, IP20 Enclosure, -20 to 70 °C, 85 mm H x 45 mm W x 85 mm D Dimensions