The SIRIUS 3RT1916-1BE00 is a varistor-type surge suppressor designed to clip voltage spikes on the control coil of Size S00 contactors. It's rated for AC control supply voltages from 240 V up to 400 V, at either 50 Hz or 60 Hz — meaning it handles the common European and North American line frequencies without a change. This is a phased-out product, so if you're filling a BOM line or a spare part kit, the official successor is the 3RT2916-1BE00.
The 240-400 V AC range covers the standard control voltages for contactor coils in most industrial panels — 230 V and 400 V line-to-line are the common taps. The varistor design means it clamps transient overvoltages rather than filtering them, so it's suited for suppressing inductive kickback from the contactor coil. It mounts directly onto Size S00 contactors in the SIRIUS series, snapping onto the front without extra wiring space. Out here in the grease, that's the kind of fit that keeps a panel rebuild on schedule.