The SIRIUS 3RT1916-1CD00-ZX90 is a surge suppressor built as an RC element rated for 127...240 V AC and 150...250 V DC. It mounts directly onto S00-size contactors to quench voltage spikes from the coil circuit — without it, the inductive kick from the contactor coil can weld auxiliary contacts or couple noise into the 24 VDC control bus. Snaps onto the contactor front without extra DIN rail space.
This part carries a current lifecycle stage but the description flags it as a phased-out product. The official successor is the SIRIUS 3RT2 series surge suppressor. If you are freezing a BOM or stocking a critical spare, the 3RT2 is the drop-in replacement path for new builds.
Designed for S00 contactor frames — the standard Siemens SIRIUS size that covers motor loads up to about 7.5 kW at 400 V AC-3. The suppressor mounts on the contactor's front face, so it does not consume additional panel width. Multi-unit packaging (10 units per pack) suggests it was intended for panel builders who order in batches rather than one-offs.