What this safety relay does on a line
The Siemens 3SK1122-1CB42 is a SIRIUS safety relay with solid-state enabling circuits, built to stop a machine when a guard opens or an E-stop drops out. It's rated SIL 3 per IEC 61508 and IEC 62061, and PL e per ISO 13849-1 — top-end integrity for a single device, meaning it covers the highest risk-reduction levels you'd typically see on a press, a robot cell, or a conveyor hazard zone. It runs on 24 V DC, and the 22.5 mm width means it snaps onto a DIN rail alongside other SIRIUS control gear without eating up panel space. Screw-type terminals take solid wire 1x 20–14 AWG or stranded 1x 20–16 AWG — standard stuff for a panel builder, no special crimps needed.
The 99 % safe failure fraction (SFF) tells you this relay detects almost every dangerous fault on its own — you're not relying on a downstream PLC to catch a stuck contact. The 60 ms minimum sensor input pulse keeps it from nuisance-tripping on short glitches, but it still responds fast enough for a guarding application. Power loss maxes out at 2 W, so you can pack several of these in a row without cooking the enclosure. The cascading design lets you link multiple units for more contacts without extra wiring — handy when you need to stop several zones from one E-stop.
Mounts in any position via screw and snap-on to a DIN rail — no special bracket. Depth is 121.6 mm, height 100 mm, width 22.5 mm; the 121.6 mm depth is a bit deeper than a standard slim relay, so check your enclosure depth if you're swapping into a tight panel. Screw terminals accept solid 1x 20–14 AWG or 2x 18–16 AWG; stranded 1x 20–16 AWG or 2x 20–16 AWG. With ferrule, 1x 0.5–2.5 mm² or 2x 0.5–1.0 mm².