The Siemens SIRIUS 3RT1916-1PB3 is an EMC suppression module designed for Size S00 contactors. It uses a varistor circuit to clamp voltage transients on the coil circuit, which is the standard method for suppressing inductive kickback on AC-operated contactors.
The 690 V rating at both 50 Hz and 60 Hz means this module handles the full range of standard industrial AC control voltages without derating — 400 V, 480 V, and 690 V line-to-line systems are all within spec. The varistor design (rather than an RC snubber or diode) means it's suited for AC coils where the suppression element must handle repeated inrush without degrading. Size S00 is the smallest SIRIUS contactor frame; this module snaps onto the contactor's coil terminals directly, so no extra DIN-rail space is consumed.