The Siemens SIRIUS 3RH1921-2FE22-ZX95 is a solid-state-compatible auxiliary switch block designed to mount on SIRIUS contactors and contactor relays in the S0 through S12 frame sizes. It provides two normally-open and two normally-closed auxiliary contacts — one set encapsulated, one set non-encapsulated — wired via spring-loaded terminals that accept 0.5 to 2.5 mm² stranded or 0.5 to 1.5 mm² with ferrule, or 20 to 14 AWG.
The mechanical service life of 5 million switching cycles is typical for a SIRIUS auxiliary block — adequate for most machine cycles but worth noting if the application demands 10+ million operations (the successor 3RH2 series offers the same figure). The compact footprint — 44 mm wide, 38 mm high, 51 mm deep — fits standard DIN-rail spacing and leaves room for adjacent devices.
Integration note: mounting on 3RT1 contactors
The evidence explicitly notes this block is intended for use with 3RT1 contactors. It mounts on the front of the contactor, adding auxiliary contacts without increasing the panel width. The spring-loaded terminals eliminate the need for screwdriver torque checks during commissioning — strip to 8 mm, insert, and the cage clamps automatically. For a panel builder wiring a row of SIRIUS contactors, this block clips on after the contactor is DIN-rail mounted and wired.