SIRIUS Size S3 power contactor — 55 A AC-4 at 400 V
The Siemens 3RT1044-3EB05 is a SIRIUS Size S3 power contactor rated for motor switching at 55 A in AC-4 duty at 400 V, and delivers 37 kW at 500 V or 18.6 kW at 690 V. The coil is 24 V at 50 Hz with a holding power of 30 W.
Side-by-side mounting is permitted, which simplifies multi-contactor panels. Dimensions are 163 mm height, 80 mm width, 139 mm depth — the depth (139 mm) is a key fit check for shallow enclosures. Main circuit terminals are screw-type, accepting solid conductors 2x (0.25 to 2.5 mm²) or stranded 2x (10 to 50 mm²).
Duty ratings and thermal limits
Rated for AC-2 at 400 V at 30 kW and AC-4 at 400 V at 55 A — the AC-4 figure governs plugging and inching duty where the contactor makes and breaks stalled-rotor current. Maximum switching rates: 1 000 cycles/hour for AC-1 and AC-3, 400 for AC-2, 300 for AC-4. Pollution degree 3 (industrial environment). DC switching ratings are specified per voltage: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V, 6 A at 230 V, 3 A at 400 V. Arcing time is 10 to 15 ms; shock withstand is 10.6 g for 5 ms (AC) and 6.2 g for 10 ms (AC).