What It Is and Where It Fits
The Siemens 3RB2025-1PB0 is a SIRIUS solid-state overload relay designed for contactor mounting, providing motor protection with a CLASS 10E trip curve. This means it will trip within 10 seconds at 7.2× the set current, a standard for protecting standard induction motors during starts that last up to about 10 seconds. It carries ATEX approval (PTB 06 ATEX 3001 Ex II (2) GD), confirming suitability for use in potentially explosive atmospheres — specifically as a protective device associated with equipment in Zone 1 or Zone 2 gas and Zone 21 or Zone 22 dust areas. The front face is rated IP20, so it's protected against finger contact but needs to be inside a suitable enclosure for washdown or outdoor duty.
Key Ratings and What They Mean for Fit
Rated for AC-3 duty up to 690 V, this relay can handle the voltage found on 400 V and 690 V three-phase systems common in industrial motor control centers. The pollution degree 3 rated voltage of 690 V confirms it's designed for the conductive environments typical in factory-floor panels. The auxiliary contact block provides one N/O and one N/C contact, rated for 4 A at 120 V AC and 3 A at 230 V AC. The N/C contact is typically wired in series with the contactor coil for fail-safe trip indication. The N/O can signal a PLC input for remote alarm. Note the DC ratings: 2 A at 24 V DC, 0.55 A at 60 V DC, and 0.3 A at 125 V DC — these govern performance in 24 V DC control circuits. Side clearance of 6 mm to adjacent devices is required for heat dissipation. The solid-state design dissipates only 0.05 W total (0.02 W per pole) in the hot operating state, so internal panel heating is minimal compared to a bimetallic relay. Operating temperature range is -25 to +60 °C, with storage/transport range of -40 to +80 °C. Shock resistance is 15g for 11 ms, adequate for most industrial machinery but verify if mounted on a high-vibration pump skid. Main circuit terminals accept screw-type connections for solid conductors of 0.5 to 4 mm² (or 2× 0.5 to 2.5 mm²), and AWG 14 to 10 for the main contacts. The auxiliary contact wiring uses the same terminal range.
Integration and Environment
Mounts directly onto the matching SIRIUS contactor (e.g., 3RT2 series) via the contactor mounting interface. No DIN rail required — it clips onto the contactor's top or bottom. The mounting position is any orientation, which simplifies panel layout. EMC immunity is specified: 2 kV burst on power ports, 1 kV on signal ports per IEC 61000-4-4 severity level 3, and 6 kV surge voltage resistance. This means it will operate reliably in electrically noisy environments with contactor switching and VFDs nearby, without nuisance trips. Maximum operating altitude is 2 000 m without derating. Relative humidity during operation can reach 100 %, including condensation — common in unheated enclosures in humid climates.
Sourcing and Lifecycle
No official successor or replacement has been announced. The part is available through normal distribution. For a line-down situation, confirm the specific contactor frame size it mates to (the 3RB2 series mates to SIRIUS 3RT2 contactors up to a certain frame) to ensure the mechanical interface matches your existing panel.