Siemens Introduces First Soft Starters with Integrated Safe Torque Off Functionality

Norcross, Ga. | August 13, 2020

August 13, 2020

  • Integrated motor protection function ensures fast, reliable shutdown
  • Restart interlock feature and failsafe digital input help ensure user safety 
  • Products are SIL 3 and PL e compliant and ATEX and IECEx certified 


The SIRIUS 3RW55 Failsafe soft starters are the first to feature the integrated Safe Torque Off (STO) function. This ensures that the motor comes to a complete standstill if an operator initiates an emergency shutdown. The motor then remains in this state until the restart interlock is used to restart it. 


Another important safety feature of the 3RW55 Failsafe soft starter is the integrated fail-safe digital input that directly connects to an emergency stop pushbutton. This covers SIL 1 PL c applications and even achieves a SIL 3, PL e rating when a safety contactor and relay are applied.


The STO function facilitates risk-free working, even with the protective door open, making it popular in processing machine applications and systems such as agitators or belt conveyors. These soft starters are also certified according to ATEX/IECEx directives, making them ideal for starting explosion-proof motors and for use in applications at airports, gas stations, or other work areas where explosions might occur. 


In addition to their safety benefits, the SIRIUS 3RW55 Failsafe soft starters provide savings on components and wiring, making them a popular option for control panel engineers and designers. Control panel manufacturers no longer require using several individual components to have this function, which reduces the time and effort for wiring and maintenance and saves space in the control cabinet. In addition, the switching time of the integrated solution is significantly shorter than for conventional, electromechanical components.


With their innovative torque control, the SIRIUS 3RW55 Failsafe soft starters can be used to start up to 400 hp at 480VAC for inline circuits or 750 hp at 480VAC for inside-delta circuits. Learn more about these soft starters’ comprehensive functionality at



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About Siemens

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. With around 71,000 employees worldwide, Siemens Smart Infrastructure has its global headquarters in Zug, Switzerland, and its U.S. corporate headquarters in Buffalo Grove, Illinois, USA.


Siemens Corporation is a U.S. subsidiary of Siemens AG, a global powerhouse focusing on the areas of power generation and distribution, intelligent infrastructure for buildings and distributed energy systems, and automation and digitalization in the process and manufacturing industries. Through the separately managed company Siemens Mobility, a leading supplier of smart mobility solutions for rail and road transport, Siemens is shaping the world market for passenger and freight services. Due to its majority stakes in the publicly listed companies Siemens Healthineers AG and Siemens Gamesa Renewable Energy, Siemens is also a world-leading supplier of medical technology and digital healthcare services as well as environmentally friendly solutions for onshore and offshore wind power generation. For more than 160 years, the company has innovated and invented technologies to support American industry spanning manufacturing, energy, healthcare and infrastructure. In fiscal 2019, Siemens USA reported revenue of $26.5 billion, including $1.23 billion in exports, and employs approximately 50,000 people throughout all 50 states and Puerto Rico.