Product Overview

The Siemens 3RH1921-1HA22​ is a 4-pole auxiliary switch block belonging to the SIRIUS 3RH19 product family, engineered by Siemens AG (Nuremberg / Amberg works) to extend the control-logic capability of 3RT1 motor contactors and contactor relays in Size S0 through S3. In Siemens’ low-voltage control architecture, a 3RT1 power contactor handles the 3-phase motor mains (up to AC-3 ratings of the S0–S3 frame), but the control circuit—start/stop pushbuttons, pilot lamps, interlocks to upstream/downstream starters, feedback to a PLC—needs dry auxiliary contacts that follow the contactor’s mechanical state. The 3RH1921-1HA22​ snaps onto the front of the 3RT1 body (or stacks behind other 3RH19 blocks) and delivers a balanced 2 NO + 2 NC instantaneous contact set, screw-terminated, compliant with EN 50012 pin/footprint conventions so that panels built to that standard remain vendor-interchangeable at the footprint level.The 3RH1921-1HA22​ is positioned as the “standard-density” aux block in the S0–S3 range: 2 NO + 2 NC is enough for a typical DOL starter (one NO for “contactor picked up” lamp/seal-in, one NC for “stop-circuit normal” feedback, and two spares for interlock to a reverse-contactor or a downstream overload trip). Rated insulation is 690 V AC, surge withstand 6 kV, and the front protection is IP20—consistent with cabinet-mounted contactor rows. Mechanically the 3RH1921-1HA22​ is rated for 10 million switching cycles, with contact reliability quoted at 1 faulty operation per 100 million at 17 V / 1 mA test conditions, which places it squarely in the “fit-and-forget” class for motor-starter panels that see daily cycling but not the abuse of, say, crane-duty reversing.Siemens has since moved the SIRIUS range to the 3RH2 generation, so the 3RH1921-1HA22​ is now listed “phased-out” with the 3RH2-series aux block as successor. However, thousands of panels built around 3RT1 S0–S3 contactors (2000s–2018 vintage) are still in service across water treatment, HVAC plant rooms, conveyor drives, and machine-tool auxiliaries—and those panels specify the 3RH1921-1HA22​ by material number. For MRO buyers, the part remains a high-turn spare because it’s small, cheap, and—when missing—can stall a starter-panel rebuild that otherwise only needs a contactor swap.

Technical Specifications

Main Features and Advantages

The 3RH1921-1HA22​ is one of those SIRIUS components where the value is in the ecosystem fit rather than any single headline spec. First, the snap-on front mounting. On a crowded DIN-row of 3RT1 S0–S3 contactors (say a 12-wide starter bank for a water-pump station), there is no rear access—cabinet back is against a wall. The 3RH1921-1HA22​ clicks onto the front tongue of the 3RT1 body without tools, and the actuator fork inside the block rides the same moving core that drives the power poles, so NO/NC timing tracks the main contact exactly. That means “contactor picked up” feedback to the PLC arrives within the same millisecond window as the motor mains close—no lag, no separate sensing.Second, the 2 NO + 2 NC split is deliberate for EN 50012 legacy panels. Many MRO electricians still carry a mental map: “S0 contactor gets one 2NO/2NC block max before you hit the 3RH19 stacking limit.” The 3RH1921-1HA22​ fills that sweet spot. If a designer needs 4 NO instead, they stack a second block—but for 80 % of DOL starters, 2+2 is the right density, and Siemens priced the 3RH1921-1HA22​ accordingly (it’s the volume SKU in the 3RH19 lineup).Third, the 10-million-cycle mechanical life and the 1-fault-per-100M contact reliability figure. Those numbers sound like marketing until you run a packaging-line conveyor where the contactor picks up 200×/day, 300 days/year—that’s 60 k cycles/year, so the 3RH1921-1HA22​ is good for 150+ years mechanically. The real wear item is the screw terminals loosening under vibration, not the contacts themselves. Which brings the fourth point: the screw-terminal version (-1HA22) is preferred over the spring-cage (-1FA22) in panels where maintenance crews periodically torque-check during PM—screw terminals are what most plant electricians expect on a 3RT1 row, and mixing spring + screw on the same contactor stack confuses apprentices.Finally, sparing reality: the 3RH1921-1HA22​ is phased-out. Siemens’ successor 3RH2 aux blocks have a slightly different front-footprint coding (physically coded to prevent mismating across generations), so you cannot blindly substitute a 3RH2 block onto a 3RT1 body without checking the mechanical key. For plants staying on 3RT1, keeping 3RH1921-1HA22​ on the shelf is the only sane move—crossing to 3RH2 means also crossing the contactor to 3RT2, which is a much bigger BOM change.