The Siemens 3RH1921-1FA31 is a SIRIUS auxiliary switch block designed to snap onto 3RT1 contactors, adding 4 poles of auxiliary contacts (3 normally open, 1 normally closed) in a compact 51 x 44 x 38 mm footprint. It is rated for a maximum thermal current of 10 A and carries switching capacities ranging from 10 A at 24 V up to 0.3 A at 220 V, with AC-15 ratings at 690 V of 1 A. The contact arrangement follows EN 50005, and the block uses screw-type terminals accepting 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) conductors.
This part is a phased-out product. The manufacturer lists it as a 'Phased-out product' with the official successor being the SIRIUS 3RH2 series. For BOM lines that specify the 3RH1921-1FA31, the direct replacement path is to the newer 3RH2 family, though panel re-qualification may be needed due to dimensional differences (the 3RH2 blocks are larger at 73 x 45 x 57.5 mm vs. the 3RH1921's 51 x 44 x 38 mm).
Snap-on mounting directly onto 3RT1 contactors — no tools required for attachment. The block adds 51 mm depth to the contactor assembly. Front protection is IP20, meaning it is finger-safe for panel environments but not rated for washdown. Mechanical life is rated at 10 million switching cycles typical, with contact reliability of 1 faulty switching per 100 million operations at 17 V, 1 mA.
Switching Capacity Profile
The 3RH1921-1FA31 provides two sets of switching ratings: one set for general use (maximum 10 A, with derated values at higher voltages: 6 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V) and a separate set for AC-15 duty at 690 V (1 A).