Auxiliary switch block for SIRIUS contactor relays and power contactors
The Siemens SIRIUS 3RH1921-2FA04 is a 4 NC auxiliary switch block designed for use with SIRIUS contactor relays and power contactors. It snaps onto the front of the contactor via the snap-on mounting method, adding four normally-closed auxiliary contacts to the switching assembly. Rated for a maximum of 10 A, with specific current ratings across multiple voltage levels: 6 A at 24 V, 6 A at 125 V, 6 A at 230 V, 6 A at 250 V, 3 A at 400 V, and 0.3 A at 220 V. For AC-15 duty at 690 V, the rated value is 1 A. The block uses spring-loaded terminals for the auxiliary and control circuit connections, accepting 2x (0.5... 1.5 mm²) with core end processing or 2x (0.5... 2.5 mm²) without. Mechanical service life is typical 10,000,000 switching cycles.
Lifecycle and replacement
The 3RH1921-2FA04 is a phased-out product. The official successor is the SIRIUS 3RH2 series auxiliary switch block. If you are replacing an existing 3RH1921-2FA04 in a panel, the 3RH2 block is the direct functional replacement, but verify terminal layout and mounting compatibility with your specific contactor frame (S0...S12).