Siemens 3RB1257-0KM01 Overload Relay, 125-500A, Discontinued

The 3RB1257-0KM01: The 125-500 A range covers large motor loads — think crusher drives, mill conveyors, or high-power pump sets. The thermal class is adjustable from 5 to 30, so you can match the trip curve to motor start time and stall protection needs. Busbar connection on the main circuit means the relay bolts directly onto the contactor's power bus; no separate wiring for the motor leads. The auxiliary circuit uses screw terminals, so field wiring is straightforward with standard ring or fork lugs. Ground-fault signaling is built in, which saves an external ground-fault relay in applications where earth leakage is a concern.