The Siemens 3RT1045-1BE44 is a SIRIUS S3-size power contactor — the workhorse for switching three-phase motors up to 37 kW at 400 V AC-3 duty. That AC-3 rating of 66 A is the number that matters for most motor-starting applications: it covers induction motors with moderate inrush, the kind you find on pumps, fans, and compressors on a production line. The AC-1 rating (resistive loads) and AC-4 rating (plugging/inching) are lower, so if your load is a heater bank or a reversing application, the contactor still fits but the thermal capacity shrinks accordingly. The 201 mm depth is the full body dimension; make sure your enclosure depth clears that before you cut the gland plate.
Main circuit terminals are screw-type, sized for stranded conductors from 2x (10... 50 mm²) — that's a big lug range, covering everything from a 4 mm² motor feed up to a 50 mm² bus drop. The control circuit (coil and aux) takes solid wire 2x (0.5... 1.5 mm²) or 2x (0.75... 2.5 mm²). If you're landing a 50 mm² cable on the line side, you'll need a torque screwdriver; no push-in spring here. The IP20 rating on the front means the terminals are touch-safe once the cover is on, but the terminal body itself is IP00 — don't let loose strands bridge to the panel.
Coil and switching performance
That's a fast, clean make-and-break for a contactor this size. The rated switching frequency at AC-3 is 1 000 operations per hour — fine for a conveyor or pump cycling every few seconds, but if you're doing high-speed jogging, the AC-4 limit of 300 ops/hour is the one to watch.
Environmental and mounting conditions
In practice, that means it's fine in a ventilated industrial panel but not for direct washdown zones unless enclosed.