The Siemens 3RU1900-1B is a SIRIUS cable release with a holder for RESET, measuring 400 mm long. It fits the S00, S0, S2, and S3 frame sizes of 3RU11 and 3RB20/3RB21 overload relays — the common sizes across Siemens' compact motor starter lineup.
This part is listed as a phased-out product. The official Siemens successor is the 3RU2900-1B, and the preferred successor type is also the 3RB3980-0B. For BOM lines that still call out the 3RU1900-1B, the 3RU2900-1B is the drop-in replacement to spec in — same function, same mounting footprint for S00 through S3 frames.
What it does in the panel
This cable release lets you mount the RESET button remotely from the overload relay face — useful when the relay is buried inside a panel or behind a guard door. The 400 mm length gives enough reach to bring the reset to a convenient spot on the enclosure door or subpanel. It clips onto the relay's front without tools.