Siemens 3SK1211-1BB40 Output expansions. Siemens 3SK1211-1BB40 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 4RO with relay enabling circuits 4 NO contacts plus Relay signaling circuit 1 NC contact Us = 24 V DC screw terminal.