SIRIUS S3 Power Contactor for Motor Loads
The Siemens 3RT1044-1AM20 is an S3-size SIRIUS power contactor rated for 37 kW at 500 V in AC-3 duty, meaning it handles the inrush and switching of standard three-phase squirrel-cage motors up to that load. The 690 V rating of 18.6 kW confirms its capability on higher-voltage European or marine supplies. This is the rating that governs real motor switching — not the thermal current, but the AC-3 figure that accounts for the inductive break. The contactor accepts solid conductors from 0.5 mm² up to 4 mm² on the control side and stranded conductors up to 50 mm² on the power side, covering most motor feeder sizes up to the S3 frame.
Side-by-side mounting is permitted, so multiple contactors can be ganged without spacing gaps — useful for grouped motor starters in a compact MCC section. The S3 frame dimensions are 70 mm wide by 146 mm high by 139 mm deep, fitting a standard 200 mm deep enclosure with room for wiring gutters. Front protection is IP20 with the cover or box terminal installed, which is the minimum for finger-safe touch protection inside a locked panel. The terminal area itself is IP00, so live parts are exposed during wiring — standard practice, but a reminder to de-energize before landing conductors.
The 10 million mechanical life cycles (typical) and AC-3 switching rate of 1000 cycles per hour give a realistic service life for high-cycling conveyor or pump applications.