The Siemens 3SK1122-2AB40 is a SIRIUS safety relay with solid-state enabling circuits. Operating frequency is rated up to 2,000 1/h; 24 V DC supply, maximum power loss 2 W. The safety integrity is SIL 3 per IEC 61508 and PL e per ISO 13849-1, with a safe failure fraction (SFF) of 99 %. That puts it in the highest reliability band for guarding applications — it is sized for hazard zones where a single fault must not lead to loss of the safety function, and where the probability of dangerous failure per hour is below 10⁻⁷. The three instantaneous safety contacts are the physical interface to the load contactors or motor starters. Screw and snap-on mounting. Spring-loaded push-in terminals accept solid 1x (0.5... 1.5 mm²) or 2x (0.5... 1.5 mm²) without ferrule, and stranded 1x (0.5... 1.0 mm²) or 2x (0.5... 1.0 mm²) with ferrule.
Deployment context — where this relay lives in a safety circuit
This relay is the logic-and-enabling element in a safety circuit that monitors a start input and a feedback input from external contactors or actuators. The start input expects a sensor signal with a minimum pulse duration of 60 ms; the feedback loop confirms that the downstream power contacts have opened before the enabling circuit resets. The cascading design allows multiple 3SK1 relays to be chained for multi-zone guarding without additional interface modules. The EMC emission complies with IEC 60947-5-1, Class A, suitable for industrial environments without additional filtering. Shock resistance is 10 g for 11 ms, adequate for machine-mounted panels near presses or conveyors.