The Siemens SIRIUS 3RT1916-1BF00-ZX90 is a varistor-type surge suppressor designed for mounting onto SIRIUS S00-size contactors. It clamps voltage transients from the coil circuit, protecting the contactor coil and downstream control electronics from inductive kickback. The varistor covers a 400 to 600 V AC range, which means it suits standard 400 V three-phase control circuits and 480 V line-to-line applications common in North American panels.
The suppressor snaps onto the contactor's coil terminals. It is sized specifically for the SIRIUS S00 contactor frame (45 mm width, 72 mm depth for the base contactor). No additional wiring is needed — it mounts directly across the coil terminals. For a panel that was specified around a 3RT1015-1BB42 contactor, this suppressor fits without rewiring, as both share the S00 frame and terminal layout.