The Siemens SIRIUS 3RH1921-1HA31 is a 4-pole auxiliary switch block with a 3 NO + 1 NC contact configuration, wired via screw-type terminals and designed to snap onto 3RT1 contactors in the S0 through S12 frame sizes. It carries a maximum thermal current of 10 A, with a rated operational current of 10 A at 24 V (AC-15/DC-13) and 6 A at 230 V. The block measures 51 mm deep, 44 mm wide, and 38 mm high, and is rated for 10 million mechanical operating cycles typical. Front-side IP20 protection covers the terminals.
Mounting is snap-on onto the contactor — no DIN rail required for the block itself; it clips directly to the 3RT1 contactor. The screw terminals accept two conductors per clamp: 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) with ferrule, or 2x (20 to 16) and 2x (18 to 14) AWG. Surge voltage resistance is rated at 6 kV, and the insulation voltage at pollution degree 3 is 690 V AC. The contact reliability spec — 1 faulty switching per 100 million operations at 17 V, 1 mA — means it handles low-level PLC signals without nuisance misses.