The Siemens 3RK3321-2AA10 is a SIRIUS expansion module for the 3RK32 and 3RK33 modular safety system families, adding 8 digital inputs in a 22.5 mm-wide housing. It is designed to snap onto a DIN rail and is powered by a 24 VDC control supply. The spring-loaded terminals accept conductors without tools, which speeds panel wiring and reduces the risk of loose connections under vibration.
The 124 mm depth and 105 mm height are typical for this series; verify clearance against the cabinet door and adjacent wiring ducts. The 24 VDC control supply is common across the system, and the module draws its power from the backplane bus, so no separate supply wiring is needed for the inputs.
Environmental and electrical robustness
It withstands shock at 15g for 11 ms and vibration per IEC 60068-2-6 from 5 to 500 Hz at 0.75 mm amplitude. ESD immunity is 4 kV contact / 8 kV air discharge, and burst immunity on power ports is 2 kV per IEC 61000-4-4. Operating humidity range is 10 to 95 % RH, and installation altitude is up to 2 000 m above sea level.
The module supports monitored start-up, a safety-system feature that checks the input circuit integrity before enabling the safety function. It does not provide parameterizable outputs, emergency-off function, protective door monitoring, or evaluation for enabling switches, selector switches, two-hand operator panels, or electro-sensitive protective equipment. It has no outputs for testing contact-based sensors. These are pure input expansion modules — all safety logic and output functions are handled by the base unit (3RK32 or 3RK33) they connect to.