The 3RA2120-1JA24-0BB4 is a Siemens SIRIUS direct on-line starter combining a contactor and overload relay in one Size S0 package. Trip Class 10 matches the thermal characteristic of standard induction motors, tripping within 10 seconds at locked-rotor current. The 24 VDC coil holds in on a 24 V nominal supply.
Mounting and integration — DIN rail or screw-fixed
Clearance: 50 mm upwards, 20 mm forwards, 20 mm at the side, 10 mm downwards, 0 mm backwards (–) — the 0 mm rear clearance means it can sit flush against a panel backplane.
Lifecycle and sourcing — active, fully traceable
The supplied contactor is 3RT2024-1BB40 and the link module is 3RA2921-1BA00. If you are replacing an older SIRIUS load feeder, the mounting footprint and terminal layout are consistent across the S0 frame size. No adapter plate needed for a direct swap in an existing panel.
Chain of custody — what to verify on receipt
For a part that protects a motor branch circuit, counterfeit or re-marked stock can mean a misrated overload that fails to trip. Verify the date code on the Siemens nameplate matches the packaging label. The 24 VDC coil marking should be legible and laser-etched, not a stick-on label. Full traceability back to Siemens factory batch records is available through authorised distribution channels only. A loose power connection on a motor starter is a common root cause of nuisance tripping and contactor welding.