What it is and what it does
The Siemens 3RB2025-1NB0 is a SIRIUS solid-state overload relay — a Class 10E device that protects motor circuits from sustained overcurrent by tripping within 10 seconds at 7.2× the set current. It mounts directly onto a contactor, saving DIN-rail space in the panel. Rated for AC-3 duty up to 690 V, it handles the inductive switching typical of squirrel-cage motors on conveyors, pumps, and fans. The front face carries an IP20 rating, meaning it's touch-safe for panel-side access but not washdown-rated — keep it inside the enclosure.
Key ratings and what they mean for fit
Trip class 10E is the critical spec: it means the relay will open the circuit within 10 seconds at a 7.2× overload. That's fast enough to protect standard induction motors during a stalled-rotor event, but not so fast that it nuisance-trips on normal inrush. If your motor application requires a slower trip curve (Class 20 or 30) for high-inertia loads like centrifuges, this part won't hold. Wire range on the main circuit terminals accepts 0.5 to 4 mm² solid, or two conductors of 0.5 to 2.5 mm² each — covers most motor leads up to about 4 kW at 400 V. Use ferruled stranded for reliable termination. Operating temperature spans -25 to +60 °C, with storage and transport range from -40 to +80 °C. That's fine for most indoor panel environments; derate if mounted near a heat source like a drive heatsink. Shock rated at 15 g for 11 ms — tough enough for machine-mounted panels on presses or punch lines.
Where it goes and how it mounts
This relay is designed for contactor mounting — it snaps onto the front of a matching SIRIUS contactor, not onto a DIN rail. That keeps the power wiring short and the assembly compact. Dimensions are 45 mm wide, 73 mm tall, and 75 mm deep, so it fits a standard 45 mm contactor footprint. Mounting position is unrestricted — any orientation works. Side clearance of 6 mm to adjacent devices is sufficient for ventilation.
Approvals and compliance
Carries ATEX certification PTB 06 ATEX 3001 Ex II (2) GD, meaning it can be used in the non-hazardous part of a circuit that controls equipment in a Zone 1 or Zone 21 area — common in chemical and grain-handling plants. Surge voltage resistance is rated at 6 kV, and it withstands burst transients at severity level 3 per IEC 61000-4-4 — 2 kV on power ports, 1 kV on signal ports. That's the standard for industrial control panels in heavy industrial environments.