Sirius Safety Switching Device Basic Unit Standard Series. Relay release circuits: 3 normally closed contacts plus relay signaling circuit with 1 normally open contact. Us = 24 V AC/DC. Screw connection safety switching device Sirius 3SK1 for standalone safety applications. The Basic Units Standard 3SK111 are characterized by simple and variable functionality, providing an economical entry into the world of safety switching devices. They are ideally suited for safety functions with only a few sensors and release circuits. These devices have comprehensive global approvals, making them well-suited for global use and export. The devices are available in a 24 V version or with a wide voltage range, relay or semiconductor outputs, and consistently with screw or spring-loaded connections (Push-In). Extensive accessories such as sealing covers, mounting brackets for wall installation, and coding pins facilitate handling. The safety switching devices 3SK replace the proven series 3TK28. Safety is a Sirius business.