The Siemens 3RB1246-1EM21 is a solid-state overload relay covering a 25 to 100 A AC range at 220 to 240 V, 50/60 Hz, with integrated thermistor protection and internal earth-fault detection. It provides 1NO/1NC bistable outputs for overload/thermistor and a separate 1NO/1NC for earth fault. This is a motor protection relay that sits in the control panel, typically on a DIN rail, wired between the contactor and the motor circuit — the thermistor input lets it monitor winding temperature directly, while the earth-fault channel catches ground leakage before it escalates.
The 25 to 100 A adjustable range covers the full-load current of most medium-frame induction motors up to about 45 kW at 400 V — sized for a motor nameplate, not a branch-circuit breaker. The 220 to 240 V control supply is the relay's own coil voltage, not the motor voltage; it powers the internal electronics and the bistable output relays. The integrated thermistor protection means the relay accepts a PTC thermistor chain embedded in the motor windings, so it can trip on overtemperature directly, not just on current-derived thermal image. The internal earth-fault detection adds a ground-leakage channel, which saves an external ground-fault module on the motor branch.