Safety relay with solid-state enabling circuits
The Siemens 3SK1122-2CB44 is a SIRIUS safety relay designed with solid-state enabling circuits, rated for 24 VDC control voltage. It carries a SIL 3 rating per IEC 61508 and IEC 62061, and PL e per ISO 13849-1, with a safe failure fraction of 99%. This means it is certified for use in safety functions up to the highest performance level for non-servo, electromechanical guarding applications — emergency stop circuits, light curtain monitoring, and two-hand control stations.
The 22.5 mm width and screw-and-snap-on mounting mean it fits a standard DIN-rail enclosure without crowding adjacent devices. The push-in spring terminals accept solid wire 1x (20…16 AWG) or 2x (20…16 AWG), and stranded wire with or without ferrules up to 1.5 mm². That is a typical control-panel wiring range — no special crimp tools needed for the push-in termination. The relay includes a start input and a feedback input, plus two instantaneous contacts and two delayed-switching contacts (the delayed switching is rated at 2). The minimum sensor input pulse is 60 ms, and the maximum response time is 85 ms at DC. That 85 ms window is the time from sensor activation to output state change — fast enough for most machine-guarding circuits, but verify it against your safety PLC scan cycle if you are coordinating multiple devices. The 10g / 11 ms shock resistance covers vibration from contactors and motor starters in the same cabinet.
Integration into a safety circuit
The cascading design (yes) allows multiple 3SK1 relays to be linked for expanded safety zones without additional logic modules. The EMC emitted interference is Class A per IEC 60947-5-1, which is standard for industrial environments — not for residential or light-commercial without additional filtering. Maximum operating frequency is 2000 cycles per hour, adequate for most machine-cycle applications but not for high-speed press or stamping lines running above that rate.