Siemens 3RH2911-1HA22 — 2NO+2NC Auxiliary Contact Block Guide

By Abdullah Zahid
11 min read
Siemens 3RH2911-1HA22 snap-on front mount auxiliary contact block with 2NO+2NC contacts for 3RT2 motor contactor

Siemens 3RH2911-1HA22 Auxiliary Switch Block, Front Mount, 2NO+2NC Contacts — Full Specifications and Selection Guide

If you are specifying or sourcing an auxiliary contact block for a Siemens 3RT2 contactor and the drawing calls for a 2NO+2NC instantaneous front-mount block, the Siemens 3RH2911-1HA22 is almost certainly the correct part. This snap-on auxiliary switch block from the SIRIUS 3RH2 family adds two normally open and two normally closed control circuit contacts to size S00 or S0 contactors — without affecting the main power circuit. Rated for 10A at 24V DC with screw-type terminals and a mechanical life of 10 million operating cycles, it covers the vast majority of motor control, status indication, and permissive interlock applications at a fraction of the footprint and cost of adding a separate relay.

If you have already confirmed this is the right part, check current pricing and availability at LeadTime.ca — ships worldwide.

Who Should Buy the 3RH2911-1HA22 — and Who Shouldn't

This auxiliary contact block is the correct choice when all of the following apply to your application:

  • Your base contactor is a Siemens 3RT2 series unit sized S00 or S0 — not S2, S3, or any other contactor family
  • You specifically need the 2NO+2NC instantaneous contact configuration for dual-function control logic
  • Your maximum auxiliary circuit current at operating voltage does not exceed 10A at 24V DC (or the derated values at higher voltages per the AC-15/DC-12 tables)
  • Screw-type terminal connections are acceptable for your field wiring method
  • Front-mount position is physically accessible in your enclosure layout
  • An IP20 protection class is adequate for your installation environment

If you need a contacts-only block (no NC contacts), the 3RH2911-1HA11 with its 2NO-only configuration may be the better fit. If your contactor base is size S2 or S3, the 3RH2911-1HA20 or another variant in the 3RH2 family is required — the 3RH2911-1HA22 will not mechanically seat on those frames.

On this page:

What the 3RH2911-1HA22 Actually Does in a Control System

The 3RH2911-1HA22 is a front-mounted auxiliary switch block that snaps onto a 3RT2 contactor and adds four independent control circuit contacts — two normally open and two normally closed — that operate entirely independently from the main power contacts. When the contactor coil energizes and the main contacts close, the auxiliary block's NO contacts close and the NC contacts open simultaneously, giving your control circuit a direct, real-time reflection of the contactor state.

This matters because a basic 3RT2 contactor ships with only its main three-phase power contacts. Any control logic that depends on knowing whether the contactor is actually energized — permissive interlocks, pilot light feedback, PLC digital inputs, safety relay dual-channel inputs — requires additional contacts that do not share current path with the motor circuit. The 3RH2911-1HA22 provides exactly that capability through a snap-on block that requires no tools, no additional mounting hardware, and no modification to the contactor body. The block's screw-type terminals accept solid or stranded conductors, and the entire assembly adds 36mm of width, 37.5mm of height, and 43.7mm of depth to the contactor envelope.

The SIRIUS 3RH2 family has been in production for decades and remains one of the most widely stocked auxiliary contact block families through industrial distributors globally, which matters for both initial procurement and long-term maintenance sparing.

Where This Block Sits in a Typical System Architecture

The 3RH2911-1HA22 sits at the contactor level of your motor control architecture, bridging main power switching and the control circuit layer above it. It is the component that makes the mechanical state of the contactor visible to the rest of the control system.

  • PLC output card or control relay energizes the 3RT2 contactor coil
  • 3RT2 main contacts close, connecting motor to three-phase supply
  • 3RH2911-1HA22 auxiliary block NO contacts close simultaneously, sending a confirmation signal upstream
  • PLC digital input, pilot light, or safety relay receives the auxiliary contact state as a feedback or permissive signal
  • NC contacts from the same block can simultaneously inhibit a downstream circuit or trigger an alarm if the contactor is not in the expected state

Typical Applications and Deployment Scenarios

Motor control panels for pump stations and HVAC systems are among the most common homes for the 3RH2911-1HA22. In a pump station, the auxiliary NO contact confirms the pump motor contactor has closed before a downstream pressure or flow control sequence is permitted to proceed. In HVAC applications, the NC contact is frequently wired to a building automation system input to generate an alarm if a fan or chiller contactor fails to energize on command.

In multi-motor conveyor and machine tool applications, auxiliary blocks from each stage's contactor feed permissive logic that enforces safe startup sequencing — the second motor is not allowed to start until the first motor's auxiliary NO contact confirms it is running. This prevents simultaneous inrush current events that could trip upstream protection devices.

Status indication and duty cycle monitoring are also common uses. An auxiliary contact driving a panel-mount pilot light gives operators a direct visual indication of contactor state, and the same contact can feed a PLC counter or timer to accumulate operating hours for predictive maintenance scheduling. For safety-critical circuits, dual-channel safety relays frequently use two independent auxiliary contacts — the 3RH2911-1HA22's 2NO+2NC configuration provides the redundant contact pairs needed without requiring two separate blocks.

Application Typical Deployment
Multi-motor sequencing Auxiliary NO contact from first contactor triggers enable signal for second motor soft-start
Status indication NC contact wired to PLC input; open state triggers fault alarm if contactor fails to close
Permissive interlock NO contact enables downstream circuit only after upstream equipment is confirmed running
Redundant safety shutdown Two independent contacts wired to dual-channel safety relay input terminals
Duty cycle monitoring Auxiliary contact feeds PLC counter to track operating cycles for maintenance scheduling
HVAC fan control NC contact monitored by building automation system to confirm contactor closure on command

Purchase-Decision Specs and Variant Comparison

Specification Value
Contact Configuration 2NO + 2NC instantaneous
Mounting Type Snap-on front mount (tool-free)
Compatible Contactor Base 3RT2 series, size S00 and S0 only
Max Auxiliary Current (DC-12, 24V) 10A
AC-15 Rating at 690V 1A
Insulation Voltage 690V (Pollution Degree 3)
Surge Voltage Resistance 6 kV
Mechanical Life 10,000,000 operating cycles
Operating Temperature -25°C to +60°C
Protection Class IP20

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

Model Contact Configuration Best Fit Application
3RH2911-1HA11 2NO only Status indication where no NC permissive logic is required
3RH2911-1HA22 2NO + 2NC Standard dual-function logic: permissive, interlock, and status on S00/S0 contactors
3RH2911-1HA20 Different configuration Larger contactor bases (S2, S3) — not for S00/S0 frames
Additional 3RH2 variants Various (4NO, 2NO+2NC+2CO, others) Specialized contact combinations; confirm with distributor for exact fit

If your control logic requires a standard 2NO+2NC front-mount block for a size S00 or S0 contactor, the 3RH2911-1HA22 is the correct choice — check current availability at LeadTime.ca.

Expert Verdict: When This Part Earns Its Spot on the BOM

The 3RH2911-1HA22 does its job with very little to criticize when the application is straightforward. The snap-on front mount is genuinely convenient in the field — no screwdriver, no hardware bag to lose, and a tactile click that confirms seating. The 2NO+2NC configuration covers the widest range of common control logic needs in a single block: you get both a confirming signal path and an inhibiting signal path from one part number. With 10 million mechanical operating cycles and electrical life of 200,000 cycles at AC-15 230V, this block will outlast the contactor it is mounted on in most moderate-duty applications. The contact reliability figure of 1 faulty operation per 100 million cycles at 17V and 1mA further confirms it is appropriate for low-energy PLC input signals where intermittent contact resistance would be a real problem.

Where the 3RH2911-1HA22 has real limits: it is strictly a front-mount block for S00 and S0 frame contactors, and the IP20 protection class means it is not suitable for washdown, outdoor, or high-humidity environments without additional enclosure protection. The current rating derates significantly as voltage increases — at 690V AC-15 you are down to 1A, and at 400V AC-12 you are at 3A, which rules out directly switching large solenoid coils at higher voltages without an interposing relay. If your control circuit needs time-delay contacts, spring-loaded terminals, or more than four contact pairs, you will need to look at other options in the 3RH2 family or a separate relay block. These are not flaws — they are well-understood design trade-offs in a part that is priced and sized for exactly what it does.

From a procurement standpoint, the SIRIUS 3RH2 family enjoys strong stock depth through industrial distributors globally. If you are building a panel with multiple 3RT2 contactors, it is worth bundling auxiliary blocks into the same order to consolidate shipping. If this matches your system requirements, view current stock and pricing at LeadTime.ca.

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

  • De-energize and lock out the 3RT2 contactor before mounting or wiring the auxiliary block; verify zero voltage at all terminals before proceeding
  • Align the snap-on tabs on the rear of the 3RH2911-1HA22 with the front-face slots on the S00 or S0 contactor housing and press firmly until the block clicks fully into place — no fasteners or tools required
  • Connect solid or stranded conductors to the screw-type terminals; strip insulation to the length appropriate for the terminal opening and tighten to the torque value specified in the manufacturer documentation
  • For DC circuits, observe correct polarity at each contact pair; for AC-15 inductive loads, verify the load current at your operating voltage does not exceed the derated AC-15 rating before wiring
  • Label all auxiliary contact wiring clearly against the electrical drawing before energizing; confirm each contact is wired to its intended field device — pilot light, PLC input, solenoid coil, or safety relay channel

What Engineers Get Wrong When Ordering This Part

The 3RH2911-1HA22 has a short but specific list of ways it ends up being the wrong part on the shelf. Before placing the order, run through this checklist verbatim:

  1. Confirm your base contactor is 3RT2 series, size S00 or S0 (not S2, S3, or other families)
  2. Verify you need exactly 2NO+2NC contact configuration (not 4NO, 2NO+2NC+2CO, or other combinations)
  3. Check that 10A maximum auxiliary current is sufficient for your control circuit loads
  4. Confirm screw-type terminals match your field wiring installation method
  5. Ensure front-mount auxiliary block position is accessible in your enclosure layout
  6. Verify that IP20 protection class matches your installation environment (not IP65 or higher requirement)
  7. Check that AC-15 or DC-12/DC-13 duty cycle (low-voltage control switching) matches your application
  8. Confirm snap-on mounting is compatible with your contactor (mechanical fit)

If every item on that list checks out, this is the correct part. View pricing and stock at LeadTime.ca or contact us to confirm availability before your build date.

Frequently Asked Questions

Does the 3RH2911-1HA22 work with all 3RT2 contactor sizes?

No. The 3RH2911-1HA22 is mechanically compatible with 3RT2 contactors in size S00 and S0 only. It will not snap onto S2, S3, or other contactor frame sizes. Always verify the size designation on your contactor label before ordering, and do not rely on catalog images for size confirmation.

What is the current rating for DC control circuits at higher voltages?

The rating derates significantly above 24V. At DC-12 (resistive load) with a single current path, the rating drops to 4A at 110V and 2A at 220V. For DC-13 (inductive/motor loads) at 220V with multiple current paths, the rating is 1.2A for three paths and 0.9A for two paths. Always cross-reference your operating voltage and duty category against the full derating table before finalizing the design.

Can I use the 3RH2911-1HA22 to drive a safety relay dual-channel input?

The 2NO+2NC configuration makes the 3RH2911-1HA22 a natural fit for dual-channel safety relay inputs, since two independent contact pairs are available from one block. However, the safety integrity level of the overall circuit depends on the full system design, not the auxiliary block alone. Consult your safety relay documentation to confirm contact requirements and verify the block's IEC 60947-5-1 compliance meets your safety standard requirements.

What happens if the auxiliary block contacts fail to switch even though the main contactor is closing?

First, confirm the main contactor is actually closing by listening for the audible coil click or checking another indicator. If the main contacts are confirmed closed and the auxiliary block contacts are not switching, the block likely has internal contact erosion or welding — typically caused by repeated switching of loads that exceed the rated current for the duty category. Replacing the 3RH2911-1HA22 unit is the standard corrective action; the block is not field-serviceable.

Is there a spring-loaded terminal version of this auxiliary block?

Yes, the 3RH2 family offers variants with spring-loaded (push-in) terminals. The 3RH2911-1HA22 specifically uses screw-type terminals. If your installation standard or wiring preference requires spring-loaded connections, check with your distributor for the corresponding spring-terminal variant within the 3RH2 family.

What is a realistic service life for the 3RH2911-1HA22 in a motor control application?

The mechanical life is rated at 10 million operating cycles. The electrical life at AC-15 duty (inductive switching) at 230V is 200,000 cycles. In applications where the contactor operates several times per hour, 200,000 electrical cycles could represent two to three years of service before contacts begin showing wear — actual life depends heavily on the load type, switching frequency, and whether current ratings are being respected.

Why Order From LeadTime.ca

  • LeadTime.ca ships the Siemens 3RH2911-1HA22 worldwide — no regional sourcing restrictions
  • Real-time stock and pricing visibility on the product page, with direct team access for lead time confirmation before you commit to a build schedule
  • Volume pricing available for panel builders and OEMs ordering multiple auxiliary blocks with contactor assemblies
  • Hard-to-source and short-lead-time parts are a core focus — the team can advise on availability and alternatives when standard lead times do not fit your timeline

At-a-Glance Summary

  • Part: Siemens 3RH2911-1HA22 — Auxiliary Switch Block, Front Mount, 2NO+2NC Contacts
  • Contact configuration: 2 normally open + 2 normally closed, instantaneous operation
  • Maximum auxiliary current: 10A at 24V DC (DC-12, single path); derates to 1A at 690V AC-15
  • Mechanical life: 10,000,000 operating cycles; electrical life: 200,000 cycles at AC-15, 230V
  • Contact reliability: 1 faulty operation per 100 million cycles at 17V, 1mA
  • Mounting: Tool-free snap-on front mount; no fasteners required
  • Terminals: Screw-type; accepts solid and stranded conductors
  • Compatible base: 3RT2 contactors, size S00 and S0 only — not S2, S3, or other families
  • Dimensions: 36mm W x 37.5mm H x 43.7mm D
  • Operating temperature: -25°C to +60°C; storage: -55°C to +80°C
  • Protection class: IP20; insulation voltage: 690V (Pollution Degree 3); surge resistance: 6 kV
  • Standard compliance: IEC 60947-5-1
  • Product family: Siemens SIRIUS 3RH2