The Siemens 3RH1921-1FA11 is a SIRIUS attachable auxiliary switch block, 2-pole with 1 normally open and 1 normally closed contact, designed for snap-on mounting onto contactors in the 3RT1 series. It carries a maximum continuous current rating of 10 A, with specific switching capacities defined across a range of control voltages — 6 A at 24 V AC/DC, 6 A at 125 V, 6 A at 230 V, and 3 A at 400 V, among others — making it suitable for signaling and interlocking circuits in motor control centers and industrial panels.
Contact Ratings and Application Context
The 10 A maximum rating applies across the board, but the real selection parameter is the voltage-specific switching capacity. At 24 V it switches 6 A; at 110 V it drops to 1 A; at 220 V it handles 0.3 A. This derating curve means the block is best applied in low-voltage control circuits (24–125 V) where it delivers its full 6 A capability. The AC-15 rated value at 690 V is 1 A, confirming its use in auxiliary contactor and relay circuits rather than main power paths. Mechanical service life is rated at 10,000,000 switching cycles typical, with contact reliability specified as 1 faulty switching per 100 million operations at 17 V, 1 mA — a strong indicator for high-cycle applications like conveyor interlocking or safety gate monitoring.
Integration and Mounting
Snap-on mounting directly onto 3RT1 contactors — no tools required for attachment. Dimensions are compact: 44 mm wide, 51 mm deep, 38 mm high. The screw-type terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) with core end processing, or 2x (20–16) and 2x (18–14) AWG. Front protection class is IP20, suitable for enclosed panel installation. Insulation voltage is rated at 690 V AC with degree of pollution 3, and surge voltage resistance is 6 kV — adequate for industrial environments with moderate transient exposure.