What it is and where it fits
The Siemens SIRIUS 3RT1044-1XP00-0GA0 is a Size S3 power contactor rated for motor switching in AC-3 duty at 37 kW on a 500 V line, and 30 kW in AC-2 at 400 V. It handles both 50 Hz and 60 Hz supplies. The coil is rated for 230 V at 50 Hz. This is the screw-terminal variant, suited for panel builders who prefer traditional terminations over spring-loaded or ring-lug connections.
Mounting and integration
Mounts via screw or snap-on onto 35 mm or 75 mm standard mounting rail. The 70 mm width and 176 mm height place it in a standard S3 envelope. Side-by-side mounting is permitted, which matters when you are packing multiple contactors on a DIN rail for a multi-motor group. The screw-type terminals for the main circuit accept 2x (10... 50 mm²) stranded wire; auxiliary and coil terminals accept solid or stranded from 0.5 mm² up to 4 mm² with ferrules.
What the ratings mean for your BOM
The 37 kW at 500 V AC-3 rating tells you this contactor can switch a 3-phase induction motor of that power under starting and running conditions. The AC-2 rating of 30 kW at 400 V covers slip-ring motors or loads where the contactor makes and breaks at reduced current. Mechanical life is 10,000,000 operations typical; electrical life depends on the duty cycle, with maximum switching rates of 1,000 per hour for AC-1 and AC-3, 400 per hour for AC-2, and 300 per hour for AC-4. The auxiliary contact block (integrated) carries 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V — enough for PLC inputs or relay coils in the control circuit.