The Siemens 3RW5074-6TB04 is a SIRIUS 3RW50 series soft starter — a hybrid switching device that ramps motor voltage up and down to limit inrush current and mechanical shock on starting and stopping. It is rated for a supply of 200 to 480 V and carries a minimum settable current of 135 A, which governs the smallest motor it can protect. Trip Class is selectable between CLASS 10A, 10E (preset), and 20E per IEC 60947-4-2, so you match the overload curve to the motor's thermal capacity — 10A for standard induction motors, 20E for high-inertia loads like centrifuges or long-start conveyors.
Fieldbus and control integration
The 3RW5074-6TB04 ships with PROFIBUS onboard and supports Modbus RTU, Modbus TCP, EtherNet/IP, and PROFINET standard — covering the four common industrial Ethernet and fieldbus protocols. That means it drops into a Siemens S7 environment on PROFINET or PROFIBUS just as easily as into a Rockwell line on EtherNet/IP. No separate communication module needed for these protocols; the PROFIenergy profile is available when used with the PROFINET standard communication module. Mounting is screw-fix to a vertical surface, rotatable ±90° and tiltable ±22.5° front-to-back. Clearance requirements: 100 mm upward, 10 mm forward, 75 mm downward, 5 mm at the sides, and 0 mm backward — tight enough for a shallow enclosure but plan for top and bottom cable access.
Hazardous-area certifications
This soft starter carries ATEX, UKEX, and IECEx certification per the spec.
Operating conditions and derating
The service factor is 1, meaning no built-in overload margin beyond the nameplate rating — size the starter to the motor FLA without headroom for continuous overload. Shock resistance is 15 g for 11 ms, with potential contact lifting noted at 12 g / 11 ms, so it holds up in mobile or high-vibration installations like pump skids or genset sets.