The Siemens 3RB1262-0LM31 is a solid-state overload relay rated for 200 to 820 A, operating on a 220-240 VAC 50/60 Hz control supply. It integrates thermistor motor protection and internal earth-fault detection into a single device, with bistable 1NO/1NC outputs for overload, thermistor, and earth-fault conditions, plus a separate 1NO/1NC output for overload warning.
The 200-820 A current range covers large motor loads — think 400 VAC pumps, compressors, or conveyor drives in the 100-400 kW class. The 220-240 VAC control supply is standard for European panel auxiliary circuits; verify your control transformer taps before wiring. The integrated thermistor input (PTC) provides direct motor winding temperature monitoring, which catches overheating from blocked ventilation or stalled rotors that a thermal model alone would miss. The internal earth-fault detection adds a second layer of protection against ground leakage, reducing the need for a separate core-balance CT in many installations.
Deployment context
The bistable outputs (latching) mean the relay holds its trip state after a fault even if control power is lost — useful for remote or unattended sites where a maintenance walk-through is needed to identify the tripped motor. The separate overload warning output (1NO/1NC) allows a PLC or SCADA to log a pre-trip alarm before the motor is disconnected.