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