The Siemens 3RB1025-1QB0 is an electronic overload relay in the SIRIUS 3RB1 series, sized for contactor mounting in the S0 frame. It protects motors against overload and phase failure by monitoring current draw and tripping when the load exceeds the set threshold for too long. Rated for 6 to 25 A with a Class 10 trip curve, it responds fast enough to protect standard induction motors during a stall or jam — the Class 10 characteristic means it will trip in under 10 seconds at 7.2× the set current, which is the standard for most general-purpose motor applications like pumps, fans, and conveyors. Connection is via screw terminals, and the relay is configured for manual reset only — meaning after a trip, someone has to physically press the reset button on the device. That is intentional for applications where an automatic restart after a fault would be unsafe (e.g., a conveyor that could drop a load).
The S0 contactor mount is a standard Siemens frame size, so if you are replacing a failed unit on an existing panel, the mechanical fit and wiring footprint are consistent with other S0-mount accessories.
Deployment context
This relay mounts directly onto a Siemens S0 contactor (e.g., 3RT20 series), snapping onto the front without additional wiring between the contactor coil and the overload — the power circuit passes through the relay's bimetal or electronic sensing element. For a panel builder, that means one less wiring step and a cleaner layout. The manual-reset-only configuration is worth noting for MRO planners: if your line relies on automatic restart after a momentary overload (e.g., a chiller pump that cycles), this is not the variant you want. Look for the auto/manual reset version in the same family. But for guarding a conveyor or a mixer where a restart must be deliberate, this is exactly the right choice.