The Siemens 3RA2327-8XB30-1BB4 is a SIRIUS reversing contactor assembly — a pre-assembled unit that mechanically and electrically interlock two contactors to reverse a three-phase motor without a separate reversing starter. It ships with two 3RT2027-1BB40 contactors and the reversing kit already integrated. The AC-3 duty class covers starting and switching off squirrel-cage motors under load — the typical reversing application on a conveyor, pump, or fan. The assembly mounts on 35 mm standard DIN rail via screw or snap-on fastening.
At 480 V it carries 27 A, and at 690 V it delivers 18.5 kW — so the current limit, not the voltage, governs the motor size. For a 460/480 V supply, the 20 hp rating confirms it covers standard North American 20 hp reversing duty. Storage range is wider at -55 to +80 °C. The S0 contactor frame size is the physical footprint — 90 mm wide, 101 mm high, 107 mm deep — so check panel depth if mounting against a backplate. Main circuit terminals accept screw-type connections: 2x (1 to 2.5 mm²) solid or 2x (2.5 to 10 mm²) solid. For stranded, it takes 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²). The AWG equivalent for main contacts is 2x (16 to 12) and 2x (14 to 8). That covers typical motor leads up to about 10 mm².
The assembly includes two 3RT2027-1BB40 contactors and the 3RA2923-2AA1 reversing kit. If you're replacing a failed unit, verify that the supplied contactor coil matches your control voltage — the coil terminals are screw-type and rated at 24 V DC.
The screw option adds vibration resistance in high-shock environments; the assembly is rated for 13.5 g at 5 ms on AC and 15 g at 5 ms on DC. Clearance around the unit: 6 mm upwards, forwards, and downwards; 0 mm backwards. That 6 mm gap to adjacent devices or enclosure walls is the minimum for airflow and wiring access. The assembly has one instantaneous auxiliary contact per direction of rotation, so if you need more feedback (e.g., separate run and fault signals), plan for an add-on auxiliary contact block.