The Siemens SIRIUS 3SK1112-1BB40 is a safety relay with solid-state enabling circuits, designed for safety-related switching tasks up to SIL 3 per IEC 61508 and PL e per ISO 13849-1. It operates on a 24 V DC supply and is rated for a maximum power loss of 2 W. The unit mounts on a DIN rail via screw and snap-on fastening, occupying a 22.5 mm width — standard for compact control cabinet layouts.
What the ratings mean for fit
The SIL 3 / PL e rating means this relay can be used in safety functions up to the highest performance level for single-channel architectures — suitable for guarding applications like light curtains, two-hand controls, and emergency stop circuits where the required safety integrity demands a proven component. The safe failure fraction (SFF) of 99 % indicates that over 99 % of dangerous failures are detected by the internal diagnostics, a key figure for achieving SIL 3 without redundancy. The 24 V DC coil is the standard control voltage for industrial safety circuits. The relay includes both a start input and a feedback input, allowing monitored manual or automatic start and external contactor monitoring — typical for E-stop and guard door circuits that need to detect welded contacts downstream. Screw-type terminals accept solid wire 1x (20…14 AWG) or 2x (18…16 AWG), and stranded wire 1x (20…16 AWG) or 2x (20…16 AWG). With ferrule, the range is 1x (0.5…2.5 mm²) or 2x (0.5…1.0 mm²). This covers most panel wiring up to 2.5 mm² without special tools. The relay is rated for pollution degree 3 and overvoltage category III, meaning it is suitable for fixed industrial installations where conductive pollution may occur and where transient overvoltages from the mains supply are present. Operating temperature range is -25 to +60 °C, storage -40 to +80 °C. Shock resistance is 10g / 11 ms, and mounting position is any, giving flexibility in cabinet layout. The maximum operating frequency is 2000 switching cycles per hour.