What it is and what it does
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. It mounts via screw and snap-on onto 35 mm or 75 mm standard mounting rail — the same DIN profile that dominates European panels. At 70 mm wide and 146 mm tall, it occupies one slot in a S3 frame, which leaves room for auxiliary contact blocks on the side. The 201 mm depth is the full body dimension; make sure your enclosure depth clears that before you cut the gland plate.
Termination and wiring
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
The contactor's coil operates on DC with a pick-up time of 14 to 20 ms and an arcing time of 10 to 15 ms. 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. Mechanical life is rated at 10 million operations typical, so the armature will outlast most of the panel.
Environmental and mounting conditions
Operating temperature range is -25 to +60 °C, storage from -55 to +80 °C. The degree of pollution rating is 3 — that's conductive pollution or dry non-conductive pollution that becomes conductive due to condensation. In practice, that means it's fine in a ventilated industrial panel but not for direct washdown zones unless enclosed. Side-by-side mounting is allowed, so you can pack multiple contactors on the rail without derating for heat buildup, though the AC-3 switching frequency assumes free air around the body.