What this part is and what it does
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 contact reliability rating of one faulty switching per 100 million operations at 17 V, 1 mA makes it suitable for direct switching of PLC inputs and solid-state loads without intermediate relays.
Key ratings and what they mean for fit
Rated insulation voltage is 690 V AC at pollution degree 3, which covers 480 V and 600 V line-to-line systems with margin. Surge voltage resistance is 6 kV, matching the impulse withstand requirements of IEC 60947-1 for industrial control panels. 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 operating temperature range of -25 to +60 °C and storage range of -55 to +80 °C cover standard industrial enclosures and warehouse conditions. IP20 on the front means the block is touch-safe but not protected against moisture ingress — it belongs inside a panel, not on the machine exterior. Snap-on mounting onto 35 mm DIN rail per EN 60715 is the fastening method, so it clips directly onto the rail alongside the contactor without tools. 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.