The Siemens 3RT2015-2BG42-0CC0 is a SIRIUS 3RT2 contactor rated for AC-3 duty at 3 kW on a 400 V three-phase line, with one normally-closed auxiliary contact and a DC 125 V coil.
The DC 125 V coil means the pickup and dropout characteristics are tuned for a 125 VDC control bus — common in older industrial plants or systems with battery-backed DC supplies. The single NC auxiliary (1NC) is wired into a safety circuit or a status feedback loop, not the main power path.