What it is and where it fits
The Siemens 3RT5044-1BW40 is a SIRIUS power contactor in size S3, designed for switching motor loads in industrial control panels. It mounts on standard 35 mm or 75 mm DIN rails via screw or snap-on fastening, and the mounting position allows ±180° rotation on a vertical surface plus ±22.5° tilt forward and backward — useful when panel layout is tight. Rated insulation voltage is 1 000 V, and at 400 V 60 °C it handles 59 kW motor load — a solid figure for a contactor this size. The operating temperature range of -25 to +60 °C covers most indoor panel environments, and pollution degree 3 means it tolerates conductive pollution typical in industrial enclosures.
Key ratings and what they mean for your BOM
The 59 kW at 400 V 60 °C rating is the one that governs real motor switching — that's the AC-3 duty class figure, not a resistive-load number. It determines whether this contactor can start and stop a 59 kW induction motor on a 400 V three-phase line without exceeding thermal limits. At 690 V 60 °C it's rated for 102 kW, which gives headroom if your line runs higher voltage. The coil draws 15 W both closing and holding at DC, so the control transformer or DC supply needs to sustain that continuously, not just a surge. Auxiliary switch extension is supported, meaning you can add feedback contacts for PLC status monitoring without a separate relay. Maximum mechanical life is 10 000 000 operations typical, and the switching frequency at AC-3 is 1 000 cycles per hour — that's about one operation every 3.6 seconds, which is fine for conveyor or pump cycling but not for high-speed pick-and-place.
Sourcing and lifecycle reality
RoHS compliance is dated 03/01/2017, and the substance prohibitance date aligns with EU RoHS requirements. For cross-border shipments, expect standard Siemens compliance documentation (CE, UL, CSA) available with the shipment.
Panel integration notes
Dimensions are 70 mm wide, 146 mm high, 152 mm deep — the S3 footprint is compact for its power class. Side-by-side mounting is allowed, so you can gang multiple contactors without derating for heat buildup, as long as ambient stays within -25 to +60 °C. Main circuit terminals accept 2x (2.5 to 16 mm²) solid or stranded wire, or 2x (10 to 1/0 AWG). Screw-type terminals on both main and control circuits mean standard screwdriver termination — no special tooling needed. The fuse recommendation for type 2 coordination is gL/gG 125 A.