The Siemens 3RT1034-3EG28-0MA3 is a SIRIUS power contactor in size S2, rated for switching motor loads up to 18.5 kW at 500 V and 10 kW at 690 V.
The 18.5 kW rating at 500 V tells you this contactor handles a 25–30 A motor load on a 500 V three-phase line — common for medium-horsepower pumps or conveyors. The 10 kW at 690 V covers higher-voltage industrial networks. The auxiliary contact ratings (10 A at 24 V, 6 A at 230 V, 3 A at 400 V) define the control-circuit capacity: at 24 VDC it switches 10 A, enough for a PLC output driving multiple relays; at 230 VAC it drops to 6 A, still fine for a pilot lamp or small solenoid.
The 55 mm width and 129 mm height fit a standard 8-module DIN-rail slot. The IP20 front enclosure protects against finger contact; the terminal area is IP00, meaning bare conductors are exposed — standard for panel-mount contactors, but keep the gland plate clear of live parts.