SIRIUS S2 Power Contactor, 48 VDC Coil
The Siemens 3RT1035-1BW44 is a SIRIUS-branded power contactor in the S2 frame size, designed for switching motor loads and resistive loads in industrial control panels. It carries a 48 VDC coil rated for continuous duty, with a pickup threshold of 0.8x rated voltage and dropout at 1.1x rated voltage — meaning the coil pulls in reliably at 38.4 V and drops out at 52.8 V, giving a clean margin against brownout conditions on a 48 V control bus. Rated for 22 kW at 500 V in AC-3 duty (squirrel-cage motors) and 18.5 kW at 400 V in AC-2 duty (slip-ring motors), this contactor handles the majority of 20–30 hp motor starts in a 400 V or 480 V plant. The AC-4 rating of 35 A at 400 V covers inching and plugging applications where the contactor makes and breaks stalled-rotor current — a common requirement on crane and hoist controls. Mounts via screw and snap-on onto 35 mm DIN rail per EN 50022, and side-by-side mounting is permitted without derating, so it packs tightly in a multi-contactor motor control center section. The front face carries IP20 finger protection; the terminals are IP00, meaning the wiring compartment must be inside a closed panel or enclosure.
Termination and Wiring
Main current circuit terminals are screw-type, accepting stranded conductors from 2x 0.75 mm² up to 2x 25 mm², and solid conductors from 2x 0.5 mm² up to 2x 4 mm². The minimum permissible cross-section at 40 °C ambient is 16 mm² for the main circuit — a useful detail when sizing branch feeders for a 22 kW motor on a hot panel floor. Coil terminals accept 2x 0.75 to 2x 2.5 mm² solid or stranded, with a strip length appropriate for screw-clamp termination. The 55 mm width and 112 mm height fit the standard S2 footprint, and the 179 mm depth leaves clearance for wiring ducts and finger-safe covers in a 200 mm deep enclosure.
Lifecycle and Sourcing
Compliance documentation includes RoHS conformity dated to 05/01/2012 (substance prohibitance date), and the product carries the usual Siemens CE, UL, and CSA certifications for the SIRIUS contactor family. Pollution degree 3 rating means it is suitable for industrial environments with conductive pollution or dry non-conductive pollution that becomes conductive due to condensation.
Switching Performance and Life
Mechanical life is rated at 10,000,000 operations typical — a figure that reflects the S2 frame's robust construction for high-cycling applications like conveyor systems or pump panels. Electrical life varies by duty: AC-1 (resistive) allows up to 1,200 switching cycles per hour, AC-3 (motor start) allows 1,000 cycles/hour, and AC-4 (plugging/inching) is limited to 300 cycles/hour due to the higher arc energy at each break. Arcing time is 10 to 15 ms, and DC operating time (pickup + dropout) is 20 to 25 ms — fast enough for most PLC-controlled sequences but worth noting if the contactor is used in a time-critical safety circuit where the total break time must be under 50 ms.
Environmental Range
Operating temperature spans -25 °C to +60 °C, with storage from -55 °C to +80 °C. The wide storage range is typical for SIRIUS contactors and allows the part to be kept in unheated warehouses or shipped in cold climates without damage.