SIRIUS power contactor, size S3 — 37 kW at 500 V
The Siemens 3RT1044-1AP64 is a SIRIUS power contactor in size S3, rated for motor switching at 37 kW on a 500 V AC-3 supply. It handles the same load at 690 V for 18.6 kW, so it covers 400 V class motors comfortably with headroom. The contactor is rated for both 50 Hz and 60 Hz networks, with an operating range of 0.8 to 1.1 times nominal frequency — stable for variable-frequency drive input switching or direct-on-line starts. Screw-type terminals on the main circuit accept solid conductors from 0.5 mm² up to 4 mm² per clamp, and stranded runs from 10 mm² to 50 mm². That covers panel wiring from control-circuit taps up to the motor feeder. The auxiliary contacts handle 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V — enough for PLC feedback or status indication on the line side.
At 70 mm wide, 146 mm tall, and 188 mm deep, it fits a standard size S3 footprint — expect to leave clearance for the arcing space and terminal access.
Electrical endurance depends on the duty category: AC-1 (resistive loads) allows up to 1,000 operations per hour, AC-3 (motor starting) also 1,000 per hour, AC-2 (slip-ring motors) 400 per hour, and AC-4 (plugging/inching) 300 per hour. The arcing time sits between 10 and 15 ms, with total AC switching time from coil energization to main contact closure at 10 to 19 ms.