The Siemens 3RB2025-1RB0 is a SIRIUS solid-state overload relay — CLASS 10E trip curve, designed to bolt directly onto a contactor (contactor mounting). It protects motors against overload and phase-loss by monitoring current through the main circuit and tripping the contactor coil when the thermal model exceeds the class threshold. The 45 mm width keeps it tight on the DIN rail, and the ATEX Ex II (2) GD marking (PTB 06 ATEX 3001) qualifies it for use in potentially explosive gas or dust atmospheres — so it's not just a general-purpose relay; it's certified for Zone 1/21 and Zone 2/22 applications where a standard thermal overload would be out of compliance.
The main circuit terminals accept 0.5 to 4 mm² solid or 2x (0.5 to 2.5 mm²) stranded, which covers most motor leads up to about 2.5 kW at 400 V. Pollution degree 3 rated voltage of 690 V means it's rated for industrial environments with conductive pollution (dust, moisture) up to 690 V phase-to-phase — that's the standard for 400 V and 480 V systems with a solidly grounded neutral.
Deployment context
Mounts directly onto a contactor (contactor mounting) — no separate DIN-rail footprint needed, which saves panel width.