The Siemens 3RT5045-1AG00 is a SIRIUS power contactor in size S3, rated for motor loads up to 21.1 kW at 690 V. The 1 000 V insulation voltage and 6 kV rated surge voltage put it in the IEC 60947-4-1 class for industrial motor switching.
At 690 V it handles 21.1 kW; at 400 V and 60 °C ambient it's rated 66 kW — the thermal derate from 40 °C to 60 °C drops the minimum permissible conductor from 50 mm² to 35 mm². The AC-3 maximum switching rate is 1 000 operations per hour; AC-4 (plugging/inching) drops to 300 1/h. Coil draws 6 A at 24 V, 1 A at 110 V, 0.3 A at 220 V — match your control transformer accordingly.
Mounts on 35 mm or 75 mm standard DIN rail with screw and snap-on. Side-by-side mounting is allowed. Wire range for main contacts: 2x (2.5 to 16 mm²) solid/stranded or 2x (10 to 1/0 AWG). Auxiliary switch extension is available as a product extension.