The Siemens SIRIUS 3RT1944-5BG42 is a replacement magnet coil for size S3 contactors in the SIRIUS family. It operates on a 125 V DC control supply and uses spring-loaded (cage-clamp) connection technology for the coil terminals — no screwdriver needed on the coil wiring, which speeds up panel assembly and reduces loose-terminal callbacks. This coil is listed as a phased-out product. The official successor is the SIRIUS 3RT2 series coil for the same contactor frame size. For new designs or BOM refreshes, the 3RT2 replacement should be qualified; for installed panels, this 3RT1944-5BG42 remains the drop-in service part.
Mounts directly onto the SIRIUS S3 contactor body — size S3 (70 mm wide frame, typically 45–65 A AC-3 rated contactors). Panel builders should note the coil sits on the front of the contactor, so side-by-side mounting density is unaffected by the coil swap.
The key difference from the smaller SIRIUS S00 coil (e.g., 3RT1016-1BB42 at 24 V DC) is voltage and frame size. The 3RT1944-5BG42 is a 125 V DC coil for the S3 frame; the S00 coils are physically smaller (45 mm wide) and limited to lower contactor ratings. A panel originally specified with S00 coils cannot accept this S3 coil without changing the entire contactor base.