Integrated motor starter assembly — what ships in the box
The 3RA2125-4CA27-0BB4 is a SIRIUS non-fused direct motor starter in size S0, supplied as a pre-assembled unit containing the 3RT2027-1BB40 contactor and the 3RA2921-1BA00 link module with a thermal bimetallic overload relay. This is not a loose-parts kit — the contactor and overload are mechanically and electrically integrated at the factory, so the panel builder receives a single order code that mounts and wires as one device. The coil draw is compatible with standard 24 VDC or 24 VAC outputs from a programmable controller or relay interface.
Panel fit and mounting constraints
The starter measures 45 mm wide × 193.1 mm high × 107 mm deep. The 45 mm width matches the standard S0 feeder size and occupies a single 9 mm DIN-rail module slot plus clearance — the side clearance is listed at 9 mm. Mounting must be vertical; the device is not rated for horizontal or inverted orientation. Clearance requirements: 30 mm upwards, 10 mm forwards, 10 mm downwards, 0 mm backwards. This means the starter can sit flush against a rear panel wall, but needs 30 mm of free air above it for heat dissipation from the bimetallic overload. The pollution degree 3 rating confirms suitability for industrial enclosures where conductive dust or occasional condensation is present. For a panel near a hot process line or in an unheated warehouse, the -20 °C floor is the hard limit — below that the bimetallic element's trip curve shifts outside the CLASS 10 window.
The 3RA2125-4CA27-0BB4 carries the SIRIUS brand and is designed to IEC/EN 60947-4-1 for motor starters. Compliance documentation (RoHS, REACH, CE, UKCA, and the declaration of conformity) is available from Siemens upon request. The pollution degree 3 and the thermal overload design mean the starter meets the functional-safety requirements for standard motor protection without a separate overload relay purchase.