Siemens 3SK1211-2BB40 Motor Protection Relay Unit

Siemens 3SK1211-2BB40 is a SIRIUS safety relay designed as an output expansion module that adds four normally open safety contacts (NO) plus a dedicated signaling circuit (one NC contact) to a safety system, enabling expanded control over motor protection circuits. Powered by a 24 V DC control input and intended for DIN-rail mounting with spring-type push-in terminals, the device provides 4RO safety outputs and a signaling path within an IP20 enclosure. Safety performance includes a PFHD of 1.7×10^-9 per hour under low-demand conditions, SIL 3 and PL e ratings, and a mechanical life specification of up to 10,000,000 operating cycles. Typical applications involve extending safety-rated outputs to motor starters, safety interlocks, and guarding systems in automated machinery, where compact, reliable safety signaling and discrete output control are essential.