What this AS-i safety module does
The Siemens 3RK1405-2BG00-2AA2 is a Slimline Compact I/O module designed for control-cabinet use, carrying the AS-i SC17.5F design with 2 fail-safe digital inputs and 2 PNP transistor outputs. It is a standard AS-i slave with profile S-7.B.F, addressable via the front socket. The module provides built-in induction protection and short-circuit-proof outputs.
This module is rated up to Category 4 per EN ISO 13849-1, with a safe failure fraction (SFF) of 99 %. That means it can be used in the highest-performance safety functions — emergency stop, light curtain monitoring, two-hand control — where a single fault cannot lead to loss of the safety function. The two safety-related inputs accept mechanical contacts and are monitored for cross-faults. The 99 % SFF indicates a very low probability of dangerous undetected failures, which is what you need for SIL 3 loops.
Power supply and current draw
The module draws 0.2 A when supplied via the AS-Interface bus, or 0.5 A when supplied via the auxiliary Uaux terminal. An external auxiliary feed of 20 to 30 V DC is required for the output circuits, and must comply with IEC 60990 (PELV), protection class III. The auxiliary supply can deliver up to 4 A total. At 30 V the module draws a maximum of 270 mA; at 24 V with AS-i Power24V the same 270 mA limit applies. The AS-Interface bus itself is rated for 2 A.
Mechanical fit and panel integration
At just 17.5 mm wide — a standard single-module width on DIN rail — this module fits tight enclosures where every millimeter counts. Height is 100 mm, depth 120 mm. The screw terminals accept solid or stranded conductors: 1x or 2x 0.5 to 1.5 mm² solid, or 1x or 2x 20 to 16 AWG stranded. Finely stranded wire with ferrules is also supported at 0.25 to 1.0 mm².
Environmental limits and shock
The module withstands 15 g / 11 ms shock (modules alone) or 10 g / 11 ms with the device connector attached. These numbers matter if the cabinet is on a machine with vibration or if the panel is transported pre-wired.