As versatile as your application

A new generation of soft starters for numerous drive tasks

The right soft starter for every application

SIRIUS soft starters are the best solution when direct or star-delta starting doesn’t apply to three-phase motors, because problems can often arise due to mechanical impact in the machine or voltage drops in the line supply. Our range of soft starters with intelligent functions offers a soft alternative for almost any application, from simple to sophisticated drive requirements such as heavy-duty starting. They enable you to start three-phase motors smoothly, easily, and efficiently and implement reliable machine concepts.

Selecting and dimensioning the right soft starter

Start Simulation Tool

High Performance Sanftstarter

High performance

SIRIUS 3RW55 high performance soft starter

Thanks to its maximum functionality, the intelligent SIRIUS 3RW55 soft starter masters difficult startup and stopping processes in a soft manner. Integrated smart functions (such as pump cleaning, pump stop, automatic parameterization, and condition monitoring) support users in the smooth operation of their plant.

  • 3-phase control for optimal motor start
  • Engineering in TIA Portal
  • Various bus connections (PROFINET, PROFIBUS, Modbus)
  • Integrated operator panel with display
  • Electrical robustness
  • For drives in performance classes from 5.5 to 1,200 kW
General Performance Sanftstarter

General performance

SIRIUS 3RW52 general performance soft starters

The SIRIUS 3RW52 soft starter is the ideal alternative to star-delta starters. As an all-rounder, it is applicable for any type of drive.

  • 3-phase control for optimal motor start
  • Parameterization over rotary setting elements
  • Various bus connections (PROFINET, PROFIBUS, Modbus)
  • Operator panel with optional display
  • Electrical robustness
  • For drives in performance classes from 5.5 to 560 kW
Basic Performance Sanftstarter

Basic performance

SIRIUS 3RW30/3RW40 basic performance soft starters

Thanks to their compact design, SIRIUS 3RW30/40 soft starters are the ideal starter solution for standard applications.

  • 2-phase control for standard applications
  • Parameterization over rotary setting elements
  • Integrated motor overload protection and intrinsic device protection
  • Electrical robustness
  • For drives in performance classes from 1.5 to 250 kW

In which soft starter technology do I need to invest in the next 6 months?

To create reliable machines, our new SIRIUS 3RW5 soft starters offer you intelligent functions such as automatic parameterization, pump cleaning, and condition monitoring. So if you’re designing a new machine in the near future, we’ll support you with sophisticated solutions for pumps, compressors, fans, and conveyor belts, or with process development; regardless of whether your machine is intended for the automotive, wastewater, or the food and beverage industry.
At a glance: SIRIUS 3RW5 soft starter – the next generation

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A portfolio for all requirements

From two-phase soft starters for standard applications to high-performance three-phase soft starters, our complete portfolio encompasses all performance classes from 1.5 to 1,200 kW, making it ideal for virtually any application.
Discover the 3RW soft starters in the Siemens Industry Mall

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Smart functionalities at a glance

Thanks to comprehensive and specific functions, our powerful, coordinated portfolio of soft starters is suitable for a wide range of applications.


No matter which industry you work in, take advantage of intelligent functions such as condition monitoring, automatic parameterization, pump cleaning, and integrated brake functions.

Your application in mind

The best of two technological worlds

Hybrid switching technology combines the advantages of electronic control via power semiconductor with the low-loss conducting properties of mechanical switching contacts. In each case, the strengths of the particular technology are exploited during the appropriate operating phase.


During the motor’s startup process, the soft starter is operated via the power semiconductor, which permits a fine and targeted control of the starting current. Once the motor has been soft-started by means of the semiconductor, the low-loss switching contacts supply the current for the rest of the operating phase until shutdown.


Because hybrid switching technology reduces wear at startup, it extends the switching service life of switching devices beyond that of conventional switching technology.

Differences between the switching technologies

Benefit along the entire value chain

The digital transformation of industry continues to advance. Data plays a significant role and also simplifies planning and engineering. The Simulation Tool for Soft Starters (STS) helps users easily select the necessary devices specific to their application.


With the TIA Selection Tool, we offer you a configurator for selecting products for your project. The SIRIUS Soft Starter ES engineering tool based on the TIA Portal lets you quickly and easily parameterize, monitor, and diagnose SIRIUS general and high performance soft starters. The device parameters can be set directly on a PC and transferred to the soft starter via Ethernet cable or a PROFINET connection.


Connecting our soft starters to MindSphere, our cloud-based, open IoT operating system, gives you further options; cross-plant diagnostics, convenient process optimization, plant-wide access to control data, as well as process and measured values, predictive maintenance, energy data management, and resource optimization.

Simulation Tool for Soft Starters (STS)

With the Simulation Tool for Soft Starters (STS), we provide a convenient way to design soft starters using a simple, quick, and user-friendly interface. You just need to enter the motor and load data to simulate the application. The tool then suggests suitable soft starters.


  • Detailed, up-to-date Siemens motor database, including IE3 motors
  • Fast simulations with a minimum of input data
  • Immediate, graphical curve charts of start operations with limit values
  • Table view of soft starters suitable for the application

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SIRIUS Soft Starter ES engineering tool based on the TIA Portal

SIRIUS Soft Starter ES is the central software for project planning, commissioning, operation, and diagnosis of the SIRIUS 3RW5 General and High Performance soft starter series.

SIRIUS Soft Starter ES is seamlessly integrated into the central Totally Integrated Automation Portal (TIA Portal) Engineering Framework, thus providing users with a consistent, efficient, and intuitive solution for all their automation tasks.


  • Parameterization and diagnosis directly on the device via PROFINET.
  • Display of all operational, service, and diagnostics data
  • Important information for preventing failures or for quickly locating and correcting errors.

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More information

Here you’ll find documents and videos on our offerings as well as additional information.

Qualified expert advice for industrial controls:

Siemens Industry Mall – for fast product selection, ordering, and order tracking

Siemens Industry Mall

Discover the 3RW soft starters at the Siemens Industry Mall.