Solid-state overload relay with integrated thermistor and earth-fault detection
The Siemens 3RB1246-1EB31 is a solid-state overload relay from the SIRIUS 3RB1 series, rated for motor protection in the 25 to 100 A range. It runs on a DC 24 V control supply and packs three protection functions into one housing: overload protection via the solid-state trip curve, integrated thermistor motor protection (PTC sensor input), and internal earth-fault detection. That means a single device covers the motor branch circuit for thermal overload, winding overtemperature, and ground-fault current — no separate earth-leakage module needed.
Output configuration and bistable contacts
The relay provides two sets of output contacts: one 1NO/1NC pair for combined overload, thermistor, and earth-fault signaling, and a separate 1NO/1NC pair for overload warning only. Both are bistable outputs — they latch their state after a trip and retain it even if control power is lost. This is useful for remote fault indication on a panel HMI or a PLC digital input that needs a persistent signal until manually reset.