The Siemens 3RB1246-1PG31 is a solid-state overload relay from the SIRIUS 3RB1 family, designed for motor protection in control panels. It covers a current range of 1.25 to 6.3 A on a 110 to 120 VAC control supply at 50/60 Hz, and integrates thermistor motor protection and internal earth-fault detection into a single device.
The 1.25 to 6.3 A setting range matches small to medium induction motors — think fractional-horsepower pumps, fans, or conveyor drives. The integrated thermistor protection (PTC) means the relay directly monitors motor winding temperature, not just line current, so it catches overheating from blocked vents or frequent starts that a bimetallic overload would miss. The internal earth-fault detection adds a second layer: it senses leakage to ground without requiring a separate ground-fault module, which simplifies wiring in a panel. The bistable outputs (1NO/1NC for overload/thermistor/earth-fault, plus 1NO/1NC for overload warning) latch their state even if control power is lost — useful for remote fault indication where the PLC might not poll continuously. The 110-120 VAC coil matches standard North American control transformers; if your panel runs 24 VDC, this is not the variant for you.