Siemens 3SK1213-1AB40 Output expansions. Siemens 3SK1213-1AB40 is the exact printed commercial reference for a safety relay in the SIRIUS 3SK Safety Relays range. Siemens' official product description is: SIRIUS safety relay Output expansion 3RO Power, with Relay enabling circuits 3 NO contacts plus Relay signaling circuit 1 NC contact Us = 24 V DC screw terminal.