What it is and where it fits
The Siemens 3RH1921-2CA01-ZX95 is a front-side auxiliary switch block from the SIRIUS family, carrying one normally-closed (NC) contact in a 10 mm-wide housing. It is designed to snap onto 3RT1 contactors, adding a feedback or interlock contact without expanding the panel footprint beyond the contactor's own width. The spring-loaded terminals accept 2x (0.5... 1.5 mm²) with ferrule or 2x (0.5... 2.5 mm²) solid, matching the wiring practice on a typical DIN-rail assembly.
Rated switching capacity — what the numbers mean for your circuit
The contact is rated 10 A at 24 V (AC-15 / DC-13 equivalent), which is the headline figure for control-circuit switching. At higher voltages the current derates: 6 A at 24 V DC, 2 A at 60 V DC, 1 A at 110 V DC, and 0.3 A at 220 V DC. For AC loads at 400 V it handles 3 A, and at 690 V it carries 1 A in AC-15 duty. The 6 kV surge voltage resistance and 690 V rated insulation voltage (pollution degree 3) mean it lives comfortably in a 400 V motor-control panel without extra isolation.
Mechanical endurance and contact reliability
Rated for 10 million mechanical switching cycles typical, with a contact reliability specification of one faulty switching per 100 million operations at 17 V, 1 mA. That low-level switching capability matters for PLC inputs or safety relay feedback where dry-contact signals must be consistent over years of operation.
Environmental limits and mounting
Operating temperature range is -25 to +60 °C, storage from -55 to +80 °C. The snap-on fastening method clips directly onto the contactor's front side — no tools, no extra DIN rail space. Front protection is IP20, standard for enclosed control panels.