The Siemens SIRIUS 3RN2023-2DW30 is a thermistor motor protection relay designed for monitoring PTC thermistor (PTC) sensors embedded in motor windings. It evaluates the resistance of up to two sensor circuits and triggers an output relay when the winding temperature exceeds the PTC's rated response threshold, providing both warning and disconnection paths. The unit carries ATEX approval for use in potentially explosive atmospheres, with open-circuit and short-circuit detection active in both sensor circuits. Supply voltage is rated 24... 240 V AC/DC, covering both 50 Hz and 60 Hz systems without adjustment. The relay's output contacts are rated 1 A at 24 V, 0.2 A at 125 V, and 0.1 A at 250 V, so for a typical 24 V DC control loop the contact can switch a PLC digital input or a contactor coil directly. Galvanic isolation between the outputs prevents fault propagation between the warning and disconnection circuits.
Key ratings and what they mean for fit
The rated supply range of 24... 240 V AC/DC means the relay accepts any control voltage commonly found in industrial panels — 24 V DC, 48 V, 110 V, 230 V — without needing a separate power supply module. The initial value of 0.85 and full-scale value of 1.1 define the PTC resistance thresholds: the relay trips when the PTC resistance exceeds 1.1 times the nominal cold resistance, and resets when it drops below 0.85 times that value. This hysteresis prevents chattering around the trip point. MTBF is listed at 97 a and MTTFd at 303 a, indicating a low failure rate suitable for continuous-duty applications where unplanned downtime is costly. The relay supports auto-reset and external reset, and includes a non-volatile error memory that retains the last fault even after a power cycle — useful for diagnosing intermittent over-temperature events. Operating temperature range is -25... +60 °C, with storage and transport range of -40... +85 °C. The 22.5 mm width and any-position mounting simplify integration into crowded DIN-rail assemblies. The LED display provides local status indication for the two sensor circuits and the output relay state.