SIRIUS S0 direct starter — what ships in the box
The 3RA2125-1HE24-0FB4 is a Siemens SIRIUS direct online starter, size S0, combining a contactor, thermal overload relay, and short-circuit protection in one assembly. It ships with the 3RT2024-2FB40 contactor and the 3RV2021-1HA25 circuit-breaker pre-configured as a matched set.
Mounting and wiring — screw or snap-on, spring terminals
Mounts on 35 mm DIN rail via screw or snap-on fastening, vertical position only. The S0 footprint is 45 mm wide by 243 mm tall by 107 mm deep — plan for 50 mm clearance above and 20 mm clearance forward for wiring access. Both main power and auxiliary/control circuits terminate with spring-loaded terminals — no screw torque to check, just strip and push in. The 24 V DC coil voltage matches standard control transformer outputs in most panels.
Overload and short-circuit protection design
Thermal (bimetallic) overload release provides inverse-time protection that tracks motor heating. The magnetic short-circuit trip handles fault clearing independently of the thermal element — selectivity with upstream devices depends on the magnetic trip curve of the supplied 3RV2021-1HA25 breaker. Operating ambient range is -20 to +60 °C with 10-95% relative humidity, non-condensing. The temperature compensation keeps the trip curve stable across the band — no manual derating required for most panel environments.