The Siemens 3SK1911-3SB40 is a SIRIUS safety engineering Basic Bundle — a pre-assembled set that drops into a panel as a coordinated safety circuit. It ships as a kit containing the 3SK1112-2BB40 safety relay, two 3RT2015-1BB42 contactors, the 3RA2916-1A link module, two 3RT2916-1CB00 auxiliary contact blocks, plus the 3SU1100-0AB50-3BA0 pushbutton and 3SU1801 series enclosure components. Rated SIL 3 per IEC 61508, SIL CL 3 per IEC 62061, PL e per ISO 13849-1, and Category 4 per EN ISO 13849-1 — that's the top end of the performance level scale, meaning it's designed for safety functions where a single fault cannot lead to loss of the safety function and the fault is detected at or before the next demand.
Dimensions are 310 mm deep, 145 mm wide, 180 mm high — the width matches the standard SIRIUS 3RT2 contactor footprint, so it fits a typical 145 mm-wide DIN-rail section. Enclosure rating is IP20 with finger-safe touch protection, suitable for installation inside a locked cabinet or control panel. Connection options include both screw-type and spring-loaded terminals, giving the panel builder flexibility on termination preference. The bundle includes the 3RA2916-1A link module that mechanically and electrically bridges the contactors, reducing wiring time on the safety shutdown path.
Hardware fault tolerance is HFT = 1 (Type A device per IEC 61508-2), meaning the safety function is maintained even with one fault present. The bundle includes both a start input and a feedback input on the safety relay, so it supports monitored manual start and external contactor feedback — standard for a Category 4 emergency-stop or guard-door circuit. Maximum installation altitude is 4 000 m with derating per Siemens product notification 109792701.