Sirius Safety Switching Device Output Expansion 4RO with Relay Release Circuits, 4 Normally Open Contacts plus Relay Signal Circuit 1 Normally Closed Contact, Us = 24 V DC, Screw Connection. The Sirius 3SK1 output expansion is designed to supplement a basic device with additional safe outputs capable of switching up to 10 A. It can be connected to any 3SK basic device through wiring. All devices with a control supply voltage of DC 24 V can also be connected to the Advanced 3SK1 and 3SK2 basic devices using the device connector 3ZY12. The devices feature four safe outputs (AC-15 5 A) or three safe outputs (AC-15 10 A). There is a choice between a control voltage of 24 V or wide voltage. Available with either screw or spring clamp (Push-In) connections. The 3SK safety switching devices replace the proven 3TK28 series. Safety is a Sirius business.