The Siemens SIRIUS 3SK1 series is an emergency stop safety relay that delivers the highest levels of functional safety—PL e (ISO 13849-1) and SIL 3 (IEC 61508)—in a standardized, compact 22.5mm DIN rail housing. It is the foundational element of Siemens' SIRIUS modular safety system, designed to monitor emergency stop buttons, protective door switches, light curtains, and two-hand control stations. The 3SK1 family is characterized by its simplicity: safety functions are configured via front-panel DIP switches (on Advanced units) or slide switches (on Standard units) without the need for programming software, enabling rapid commissioning by control panel builders and maintenance technicians.

At its core, a standard 3SK1 basic unit provides three positively driven normally open (NO) safety contacts for enabling circuits and one normally closed (NC) contact for auxiliary signaling. This output configuration is expandable via the 3SK1211 output expansion modules, allowing system designers to add extra safety contacts and increase switching capacity up to 10 A. The modular architecture—using 3ZY12 device connectors—enables side-by-side mounting of basic units, input expansions, and output expansions without additional wiring. The series includes models for both 24V AC/DC and wide-range 110-240V AC/DC supply voltages, with maximum power consumption of just 2 W.

The 3SK1 portfolio is divided into two main branches: the Standard series and the Advanced series. Standard units offer essential safety functions configured via a slide switch, while Advanced units add a 4-way DIP switch for greater configuration flexibility and LED status displays. Both series feature automatic/manual/monitored start selection, cross-circuit detection, and a service life of up to 20 years. The devices operate reliably across a temperature range of -25°C to 60°C and carry global certifications including CE, UL, CSA, and TUV. Their 22.5 mm width and IP20 protection rating make them suitable for installation in control cabinets across all industrial sectors.

Compared to its successor, the software-parameterizable 3SK2, the 3SK1 excels in applications requiring straightforward, hardware-defined safety logic. While 3SK2 offers individual output control and PROFINET connectivity for complex safety tasks, the 3SK1 remains the cost-effective, time-tested solution for autonomous safety functions where simplicity and reliability are paramount. It serves as a direct, high-quality replacement for the legacy 3TK28 series, with a narrower footprint and enhanced functionality. The SIRIUS 3SK1 is the ideal safety core for standalone machine guarding, packaging equipment, material handling systems, and any application demanding certified, expandable emergency stop protection without software complexity.

Technical Specifications