Siemens 3rh1921-1ha22

By Abdullah Zahid
11 min read
Siemens 3RH1921-1HA22 SIRIUS auxiliary switch block 2NO+2NC snap-on for 3RT1 motor contactor

Siemens 3RH1921-1HA22 Auxiliary Switch Block: Specifications, Wiring, and Compatible Alternatives

When a SIRIUS motor contactor auxiliary block fails mid-shift or a new control circuit demands additional feedback contacts, the part number search ends quickly: the Siemens 3RH1921-1HA22 is the 2NO+2NC snap-on auxiliary switch block for SIRIUS 3RT1 contactors in sizes S0 through S3. This 44×38×51mm block delivers 10 million mechanical switching cycles and 200,000 electrical endurance cycles at AC-15 230V — the numbers that matter when you are verifying a replacement against your maintenance log or specifying a new interlock circuit.

If you have already confirmed this is the correct part for your contactor size and control circuit requirements, check current pricing and stock availability at LeadTime.ca — ships worldwide.

Who Should Order the 3RH1921-1HA22 — and Who Should Look at Alternatives

This block is the right choice for engineers and technicians who need to add or replace auxiliary signaling contacts on an existing SIRIUS 3RT1 motor contactor installation. Buy this part if all of the following apply:

  • Your contactor is a confirmed SIRIUS 3RT1 series in size S0, S1, S2, or S3
  • Your control circuit requires exactly 2 normally open and 2 normally closed instantaneous contact pairs
  • Your auxiliary circuit voltage and current fall within the rated AC-12, AC-15, DC-12, or DC-13 categories (up to 690V insulation voltage)
  • Your installation uses snap-on mounting and screw-terminal wiring with conductor cross-sections of 0.5–2.5mm²
  • Your application does not require SIL-rated safety-function certification — this block is not certified for safety-related duty per IEC 61508

If you need a different contact count — 1NO+1NC or 3NO+1NC — or require a dedicated DC auxiliary block for high-voltage DC circuits above 440V, the 3RH1921-1HA12 or 3RH1921-1HA31 variants are the correct alternatives. Also note: this product is listed as phased-out on current Siemens portals, so confirm stock with your distributor before locking it into a project schedule.

On this page:

What the 3RH1921-1HA22 Actually Does in a Motor Control System

The Siemens 3RH1921-1HA22 is an auxiliary switch block — a snap-on accessory that mounts directly to a SIRIUS 3RT1 motor contactor and provides four additional isolated contacts: 2 normally open and 2 normally closed, all instantaneous. It does not switch main power. Its entire job is to extend the signaling and logic capability of the contactor into the control circuit: status feedback, alarm outputs, interlock permissives, and equipment sequencing signals.

The block conforms to DIN EN 50012, which governs auxiliary equipment dimensions and mechanical interfaces for motor contactors, and its contacts are rated across AC-12, AC-15, DC-12, and DC-13 duty cycle categories. At AC-15 230V — the category most commonly used for inductive loads like relay coils and solenoids — the electrical endurance is 200,000 switching cycles. Mechanical life is rated at 10 million switching cycles, and contact reliability is specified at 1 faulty switch per 100 million operations. These are not marketing claims; they are the figures published in Siemens SIRIUS technical documentation and are the baseline a maintenance engineer should use when evaluating replacement intervals in high-duty-cycle applications.

The block accepts screw-terminal wiring with conductor cross-sections from 0.5mm² to 2.5mm², covering the full range of control cable sizes used in standard industrial panels. Surge voltage resistance is rated at 6 kV, and insulation voltage at Pollution Degree 3 is 690V — making it suitable for control circuits in environments with moderate dust or condensation.

Typical System Architecture: Where This Block Sits in the Signal Chain

The 3RH1921-1HA22 snaps onto the face of the power contactor and bridges the gap between the contactor's mechanical state and the downstream control logic that needs to know about it.

  • Control power supply (24V DC or 110/230V AC transformer) feeds the contactor coil circuit and the auxiliary circuit independently
  • PLC output card or manual control switch energizes the contactor coil, causing the main power contacts to close
  • 3RH1921-1HA22 block, mounted on the 3RT1 contactor face, changes state simultaneously with the main contacts
  • NO contacts close and feed status signals to PLC input cards, indicator lamps, or downstream relay coils
  • NC contacts open and break interlock signals to prevent simultaneous energization of a second contactor (forward/reverse, parallel pump, or incompatible equipment)

Industries and Use Cases Where This Block Is Specified

In water treatment and wastewater facilities, the 3RH1921-1HA22 is a standard fit for duty-standby pump sequencing: the NO contact confirms that the duty pump contactor has engaged and triggers the standby pump interlock; the NC contact locks out the second contactor while the first is running. At AC-12 24V and 10A, the block handles long control cable runs to remote pump panels without deration.

In manufacturing and heavy processing — conveyor lines, compressor control panels, crusher sequencing — the block provides the interlock NC contact that prevents a forward and reverse contactor from energizing simultaneously. The 200,000-cycle electrical endurance rating at AC-15 230V maps well to moderate-duty conveyor applications running multiple starts per hour across a production shift.

HVAC and building system integrators use this block for fan staging and chiller protection circuits, where the NO contact feeds a BMS input confirming fan motor status, and the NC contact coordinates thermal protection relay logic. The operating temperature range of -25°C to +60°C covers mechanical room installations without additional derating.

Control panel OEMs building standardized SIRIUS-based motor control centers specify this block across multiple contactor assemblies to maintain a uniform wiring and replacement strategy. The compact 44×38×51mm footprint allows it to fit panel layouts already designed around the 3RT1 contactor envelope without modifying busbar or DIN rail spacing.

Application Typical Deployment
Pump duty/standby sequencing NO contact confirms run state to PLC; NC locks out standby contactor
Forward/reverse motor interlock NC contact on each contactor breaks the opposite coil circuit
Conveyor and crusher sequencing NO feedback to SCADA; NC blocks downstream belt until upstream is running
HVAC fan staging and chiller control NO contact to BMS input; NC coordinates thermal relay logic
PLC diagnostic feedback NO contact wired to digital input module to confirm contactor closure
Legacy panel retrofit Drop-in replacement on existing 3RT1 contactor without wiring modification

Key Specifications and Electrical Ratings

Parameter Value
Contact Configuration 2 NO + 2 NC (instantaneous)
Compatible Contactor Series / Sizes SIRIUS 3RT1, sizes S0, S1, S2, S3
Mounting Type Snap-on to contactor face
Terminal Type Screw-type; 0.5–2.5mm² conductor range
Electrical Endurance (AC-15 at 230V) 200,000 switching cycles
Mechanical Life 10 million switching cycles
Insulation Voltage (Pollution Degree 3) 690V
Surge Voltage Resistance 6 kV
Operating Temperature Range -25°C to +60°C
Dimensions (W × H × D) 44mm × 38mm × 51mm

Full technical specifications are available on the product page at LeadTime.ca.

3RH1921-1HA22 vs. Other SIRIUS Auxiliary Block Variants: Which One Do You Actually Need?

Model NO Contacts NC Contacts Best Fit Application Mounting
3RH1921-1HA12 1 1 Simple interlock, single pilot light feedback Snap-on, 3RT1 S0–S3
3RH1921-1HA22 2 2 Complex interlocks, dual feedback circuits, PLC diagnostics Snap-on, 3RT1 S0–S3
3RH1921-1HA31 3 1 Extended logic, multi-equipment sequencing with minimal NC Snap-on, 3RT1 S0–S3

If your logic circuit requires exactly 2 NO and 2 NC instantaneous contacts on a SIRIUS 3RT1 contactor, the 3RH1921-1HA22 is the correct selection — check current availability and pricing at LeadTime.ca.

Expert Verdict: Reliability, Limits, and Procurement Reality

The 3RH1921-1HA22 earns its place in control panels through a straightforward combination of proven reliability and mechanical simplicity. The 10 million mechanical switching cycle life and 1-faulty-switch-per-100-million-operations contact reliability figure are the kind of specifications that let a maintenance engineer confidently defer proactive replacement until electrical endurance thresholds are approached. The 44×38×51mm footprint is small enough that this block fits any panel already built around the 3RT1 contactor series — no layout changes, no additional DIN rail, no enclosure modification. For replacement and retrofit work on existing SIRIUS installations, that combination of direct compatibility and compact size is the core value proposition.

The honest limits are worth stating clearly. This block is not SIL-certified and is not suitable for safety-related duty under IEC 61508 — if your interlock circuit is part of a documented safety function, you need a positively driven safety-rated device. The product is also listed as phased-out on current Siemens SiePortal listings; that does not mean it is unavailable today, but it does mean availability will tighten over time. High-volume new installations that need a 20-year support horizon should evaluate whether standardizing on the 3RH1921-1HA22 is the right long-term call or whether migrating to a currently supported SIRIUS module is worth the engineering cost now. For legacy system maintenance and short-to-medium-run new builds, however, legacy stock availability through authorized distributors remains the practical path. If this block matches your system requirements, view current stock and pricing at LeadTime.ca.

On the procurement side: because this is a phased-out product, lead times are not predictable the way they are for current catalog items. Standard stock from authorized distributors typically ships in 2–4 weeks, but if standard inventory is depleted, sourcing through surplus or legacy channels can extend that to 8–12 weeks. The practical response for any facility where this contactor is on a critical production circuit is to carry 1–2 spare blocks in plant inventory. Volume pricing is available — contact LeadTime.ca for a quote if you are ordering in quantity or need to confirm availability before committing to a maintenance schedule.

For volume pricing or to confirm lead time before committing to a build, contact the LeadTime.ca team directly — we ship worldwide.

Wiring and Installation Overview

The following is a high-level installation reference. For full wiring diagrams and step-by-step commissioning procedures, consult the Siemens SIRIUS 3RH1921-1HA22 product documentation.

  • De-energize the control circuit completely and verify zero voltage with a multimeter before handling the contactor or block
  • Align the block with the snap-on mounting rails on the 3RT1 contactor face and press firmly until the block seats with an audible click; verify it does not shift under manual tension
  • Strip 6–8mm of insulation from conductor ends; for conductors at 2.5mm², use ferrule-crimp terminals to prevent strand spreading under the screw terminal
  • Tighten each screw terminal until snug — over-tightening risks terminal fracture; confirm each conductor is held with a gentle tug
  • After applying control voltage, verify NO contacts read near-zero voltage (closed path) when the contactor is energized, and NC contacts read full control voltage (open path); reverse-test with contactor de-energized and document baseline readings

Wrong-Part Prevention: Critical Checks Before You Order

This checklist is drawn directly from the technical verification requirements for the Siemens 3RH1921-1HA22. Work through every item before placing your order — a wrong part on a phased-out product costs time you may not have.

  1. Verify contactor is 3RT1 series and confirm its size (S0, S1, S2, or S3) before ordering
  2. Confirm 2NO+2NC contact count is correct for your logic circuit (do not substitute with 3NO+1NC variants)
  3. Check maximum voltage and current in auxiliary circuit—product is not rated for line-to-line power; supports only control voltages and signals up to 690V
  4. Confirm snap-on mounting will align with your contactor; magnetic contactors use different blocks than non-reversing types
  5. Verify screw-terminal conductor cross-section compatibility (0.5–2.5mm² for auxiliary, per voltage/current rating)
  6. Do not use for DC-12 applications above 600V or DC-13 applications above 440V without derated current compliance
  7. If application requires safety functions (SIL rating), verify that this device is not certified for safety-related duty (SIL certification not listed)
  8. Check supply date availability—product is phased-out on Siemens current lists; confirm legacy stock with distributor

If any item on this checklist raises a flag, contact the LeadTime.ca team before ordering — we can confirm compatibility, check live stock, and identify the correct alternative variant if needed.

Frequently Asked Questions

Is the 3RH1921-1HA22 still available, or is it fully discontinued?

The 3RH1921-1HA22 is listed as phased-out on current Siemens SiePortal catalog listings, but legacy inventory remains available through authorized industrial distributors. Standard lead times are typically 2–4 weeks from stock; if distributor inventory is depleted, sourcing may extend to 8–12 weeks. Confirm availability with your distributor before committing to a project schedule, and consider stocking 1–2 spare units if this block is on a critical production circuit.

What is the difference between the 3RH1921-1HA22 and the 3RH1921-1HA12?

The 3RH1921-1HA12 provides 1 NO and 1 NC contact, while the 3RH1921-1HA22 provides 2 NO and 2 NC contacts. Both share the same snap-on mounting interface and are compatible with SIRIUS 3RT1 contactors in sizes S0–S3. Choose the 3RH1921-1HA22 when your control circuit requires dual feedback paths, dual interlock contacts, or simultaneous signals to both a PLC input and an alarm device.

Can the 3RH1921-1HA22 be used on DC control circuits?

Yes, but with important current derating at higher voltages. At DC-12 24V the rated current is 10A, but at DC-12 220V the current drops to 1A. DC-13 ratings are lower than DC-12 at equivalent voltages. Do not use for DC-12 applications above 600V or DC-13 applications above 440V without verifying derated current compliance against your application load. Consult the Siemens datasheet current tables for the exact value at your operating voltage and duty cycle category.

Does the 3RH1921-1HA22 qualify for SIL-rated safety functions?

No. The 3RH1921-1HA22 is not positively driven per IEC 60947-5-1 and carries no SIL certification under IEC 61508. It is not suitable for use in safety-related duty circuits where a SIL rating is required by your functional safety assessment. Applications requiring certified safety contacts must use a dedicated safety relay module with the appropriate certification documentation.

What conductor sizes are compatible with the screw terminals on the 3RH1921-1HA22?

The screw terminals accept conductors from 0.5mm² to 2.5mm², covering finely stranded and solid conductors. The AWG equivalents span 20–16 AWG (2 paths) and 18–14 AWG (2 paths). For conductors at the 2.5mm² upper limit, ferrule-crimp terminals are recommended to prevent strand spreading under the screw and to maintain reliable contact force over the life of the installation.

What happens if the 3RH1921-1HA22 approaches its electrical endurance limit in a high-duty application?

At high duty cycles — more than approximately 5 switching operations per minute sustained — the 200,000-cycle electrical endurance at AC-15 230V can be reached faster than the mechanical life of 10 million cycles. When electrical endurance is approached in a critical application, schedule proactive replacement before contact degradation causes intermittent operation. There are no user-serviceable components in the block; replacement of the entire unit is the correct maintenance action.

Why Source the 3RH1921-1HA22 From LeadTime.ca

  • LeadTime.ca ships worldwide — no geographic restriction on orders, regardless of project location
  • Phased-out and legacy Siemens SIRIUS parts are a sourcing specialty; LeadTime.ca maintains access to authorized distribution channels for hard-to-find catalog items
  • Volume pricing is available for bulk orders — contact the team directly for a quote on multi-unit purchases
  • Fast response on stock confirmation and lead time queries — critical when a production line is down and you need a verified ship date before committing

At-a-Glance Summary

  • Model: Siemens 3RH1921-1HA22 — Auxiliary Switch Block, 2NO+2NC, SIRIUS product family
  • Compatible contactors: SIRIUS 3RT1 series, sizes S0, S1, S2, and S3 only
  • Contact configuration: 2 normally open + 2 normally closed, instantaneous, isolated auxiliary circuit
  • Electrical endurance: 200,000 switching cycles at AC-15 230V
  • Mechanical life: 10 million switching cycles; contact reliability 1 faulty switch per 100 million operations
  • AC-12 rated current: 10A at 24V, 6A at 230V, 3A at 400V
  • DC-12 rated current: 10A at 24V, derated to 1A at 220V
  • Insulation voltage (Pollution Degree 3): 690V; surge voltage resistance: 6 kV
  • Dimensions: 44mm × 38mm × 51mm; mounting: snap-on; terminals: screw-type, 0.5–2.5mm²
  • Operating temperature: -25°C to +60°C; not SIL-certified; not rated for outdoor or marine environments
  • Product status: phased-out on current Siemens catalog; legacy stock available through authorized distributors; confirm availability before project commitment
  • Standards: DIN EN 50012, IEC 60947-4-1, IEC 60947-5-1