What this SIRIUS S3 contactor is rated for
The Siemens 3RT1044-3BD40 is a SIRIUS S3 power contactor with screw-type terminals on the main current circuit. It's rated for AC-2 duty at 30 kW at 400 V — that's the slip-ring motor switching category, where the contactor makes and breaks the rotor circuit under load. For AC-4 duty (plugging, inching, reversing) it's rated 55 A at 400 V. Those are the numbers that decide fit for a motor control center. At 500 V it handles 37 kW, and at 690 V it's rated 18.6 kW. The operating temperature range is -25 to +60 °C, with storage from -55 to +80 °C. Pollution degree 3 means it's suited for industrial environments with conductive contamination.
Mounting and panel fit
Mounts via screw or snap-on onto 35 mm and 75 mm standard mounting rail. The S3 frame size is 70 mm wide, 146 mm high, 152 mm deep — that's the footprint you need to clear in the enclosure. Side-by-side mounting is allowed, so you can gang contactors without a gap, but watch the thermal derating when packing them tight. Front protection is IP20 with the cover or box terminal installed; the terminal itself is IP00. That's typical for panel-mount gear — the enclosure provides the real ingress protection.
Lifecycle and sourcing reality
RoHS compliance is documented with a substance prohibitance date of 05/01/2012, covering the standard EU restricted substances. The SIRIUS series is widely stocked across distribution channels, so sourcing is straightforward — quoted to order against an RFQ.
Terminal wiring specs
Main circuit terminals accept solid conductors 2x (0.25 to 2.5 mm²) and stranded 2x (10 to 50 mm²), plus 2x (2.5 to 16 mm²) for the solid-or-stranded range. That covers everything from control wiring to heavy motor feeders. Arcing time is 10 to 15 ms at DC, with a dropout delay of 14 to 20 ms.