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Siemens’ new Sirius soft starters enable safe, efficient motor switching

Siemens Smart Infrastructure expanded its soft starters portfolio for motors, with the launch of Sirius 3RW55 Failsafe and Sirius 3RW50.

"An abrupt start or stop of motors can often cause serious problems due to mechanical impact on the machine or voltage dips in the power supply system. As part of a smart electrical infrastructure in buildings and industrial plants, the new soft starters from the Sirius portfolio offer a softer, and even safer alternative, preventing malfunctions and downtimes," said Erich Fröhlich, Product Manager at Siemens Smart Infrastructure, Business Unit Control Products.
The Sirius 3RW55 Failsafe soft starters are suited for starting and stopping operations of high-power motors with a rated output of 5.5 to 560 kilowatt (kW) at 400 volts (V). All switching operations can be controlled simply, in a user-friendly manner, via the integrated human-machine interface (HMI). Optional communication modules allow for function expansions as needed, for example offering a complete diagnosis, statistic data and measuring values for an automation system.
The Sirius 3RW50 devices have a compact, space-saving design with minimal power loss. They cover a power range from 75 kW to 315 kW at 400 volts (V) and are designed for standard applications. Additional functions can be added via optional communication modules. The integrated soft torque function helps prevent current surges at startup and reduce mechanical loads when starting and stopping motors. This makes soft starters ideal for turning on pumps because they prevent pressure spikes in the pipe system and potential damage resulting from water hammer. They are ATEX- and IECEx-certified and can also be used for applications in potentially explosive areas, for example, at airports or gas stations, when pumping kerosene or gasoline.
Motor data can be visualized via an HMI interface on the control panel door or an analog output. Modern hybrid switching technology ensures efficiency, energy-saving and a long product lifetime.
All soft starters from the Siemens Sirius 3RW5 portfolio have functions for easy and error-free parameterization, current limitation with motor overload protection and pump start and stop. They can be integrated in the Totally Integrated Automation (TIA) Portal and fully configured via the open Industrial Ethernet network Profinet, for example. Thanks to a number of certificates and approvals, for example in compliance with standards from the International Electrotechnical Commission (IEC), the Underwriters Laboratories (UL) and the Canadian Standards Association (CSA), the devices can be used worldwide.
For further information on Siemens Smart Infrastructure, please see
For further information on Sirius soft starters, please see
Siemens Smart Infrastructure (SI) is shaping the market for intelligent, adaptive infrastructure for today and the future. It addresses the pressing challenges of urbanization and climate change by connecting energy systems, buildings and industries. SI provides customers with a comprehensive end-to-end portfolio from a single source – with products, systems, solutions and services from the point of power generation all the way to consumption. With an increasingly digitalized ecosystem, it helps customers thrive and communities progress while contributing toward protecting the planet. SI creates environments that care. Siemens Smart Infrastructure has its global headquarters in Zug, Switzerland, and has around 71,000 employees worldwide.
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Siemens AG (Berlin and Munich) is a global technology powerhouse that has stood for engineering excellence, innovation, quality, reliability and internationality for more than 170 years. The company is active around the globe, focusing on the areas of electrification, automation and digitalization. One of the largest producers of energy-efficient, resource-saving technologies, Siemens is a leading supplier of efficient power generation and power transmission solutions and a pioneer in infrastructure solutions as well as automation, drive and software solutions for industry. With its publicly listed subsidiary Siemens Healthineers AG, the company is also a leading provider of medical imaging equipment – such as computed tomography and magnetic resonance imaging systems – and a leader in laboratory diagnostics as well as clinical IT. In fiscal 2018, which ended on September 30, 2018, Siemens generated revenue of €83.0 billion and net income of €6.1 billion. At the end of September 2018, the company had around 379,000 employees worldwide. Further information is available on the Internet at
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Heidi Fleissner

Smart Infrastructure

Siemensstr. 10
93055 Regensburg

+49 (173) 7383392