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Siemens 3RH1921-1XA22-0MA0 Specs: 2NO+2NC Auxiliary Contact Block Guide
The Siemens 3RH1921-1XA22-0MA0 is a SIRIUS 3RH19 front-mounted auxiliary contact block featuring two normally open (2 NO) and two normally closed (2 NC) instantaneous contacts. It uses screw terminals and is designed for specified Siemens 3RT1 contactors, particularly configurations with sequence numbers 5–8. The block expands the available auxiliary contacts for control, signaling, and interlocking circuits. Its most important selection requirements are the contactor series, frame size, mounting arrangement, and electrical utilization category.
Siemens 3RH1921-1XA22-0MA0 Technical Specifications
This accessory adds four auxiliary switching contacts to a compatible contactor or contactor relay. Unlike a power contactor, it does not independently switch the main motor supply.
| Specification | Details |
|---|---|
| Manufacturer | Siemens |
| Product family | SIRIUS 3RH19 |
| Complete model number | 3RH1921-1XA22-0MA0 |
| Product type | Front-mounted auxiliary contact block |
| Contact configuration | 2 NO + 2 NC |
| Contact operation | Instantaneous |
| Terminal connection | Screw terminals |
| Mounting method | Front snap-on mounting |
| Intended contactor series | Specified Siemens 3RT1 configurations |
| Contact sequence designation | 5–8 |
| Rated insulation voltage | 690 V |
| Rated impulse withstand voltage | 6 kV |
| Front protection rating | IP20 |
| AC-15 operational current at 230 V | 6 A |
| AC-15 operational current at 400 V | 3 A |
| AC-15 operational current at 690 V | 1 A |
| DC-13 operational current at 24 V | 6 A |
| DC-13 operational current at 110 V | 1 A |
| DC-13 operational current at 220 V | 0.3 A |
| Mechanical service life | 10 million operating cycles, typical |
| Operating temperature | -25°C to +60°C |
| Storage temperature | -55°C to +80°C |
| Weight | Approximately 71–75 g, depending on datasheet revision |
| Dimensions (W × H × D) | Approximately 44 × 38 × 51 mm |
Source: Siemens official 3RH1921-1XA22-0MA0 datasheet and the Siemens SIRIUS IC 10 catalogue.
How Does the 2NO+2NC Auxiliary Contact Block Work?
The 3RH1921-1XA22-0MA0 expands the control-circuit functionality of a compatible contactor. When the main contactor mechanism operates, the auxiliary block’s contacts change state through its mechanical connection.
Its four instantaneous contacts are arranged as follows:
| Contact terminals | Contact type | Normal state |
|---|---|---|
| 53–54 | NO | Open |
| 61–62 | NC | Closed |
| 71–72 | NC | Closed |
| 83–84 | NO | Open |
When the contactor operates, the normally open contacts close while the normally closed contacts open. When the contactor returns to its de-energized state, the contacts return to their normal positions.
This arrangement allows one contactor to provide multiple control signals without requiring four separate auxiliary switching devices.
What Do 2 NO and 2 NC Contacts Mean in Industrial Control?
The contact configuration determines how the auxiliary block interacts with the control circuit.
- Normally open contacts: Used for run-status signaling, auxiliary commands, and control logic that activates when the contactor operates.
- Normally closed contacts: Used for interlocking circuits, status monitoring, and control sequences that require a contact to open during operation.
For example, an industrial machine may use one NO contact to send a running signal to a PLC and another NO contact to activate an auxiliary control circuit. The NC contacts can be incorporated into separate interlocking or monitoring arrangements.
However, the contact configuration alone does not establish a safety-rated function. Safety-related circuits require the appropriate certified components and complete system design.
Electrical Ratings: AC-15 and DC-13 Explained
Auxiliary contact ratings depend on the electrical load and utilization category. The 3RH1921-1XA22-0MA0 has different permissible operating currents for AC and DC control applications.
| Utilization category | Voltage | Operational current |
|---|---|---|
| AC-12 | 24 V | 10 A |
| AC-12 | 230 V | 10 A |
| AC-15 | 24 V | 6 A |
| AC-15 | 230 V | 6 A |
| AC-15 | 400 V | 3 A |
| AC-15 | 690 V | 1 A |
| DC-13 | 24 V | 6 A |
| DC-13 | 110 V | 1 A |
| DC-13 | 220 V | 0.3 A |
AC-15 is relevant to controlling electromagnetic loads such as contactor coils. DC-13 addresses DC electromagnetic control loads, where switching behavior differs from resistive circuits.
Therefore, an auxiliary contact rated for 10 A under AC-12 conditions should not automatically be treated as capable of switching 10 A under AC-15 or DC-13 conditions. Always use the rating corresponding to the actual load category.
Compatibility: Which Siemens Contactors Can Use 3RH1921-1XA22-0MA0?
Compatibility is one of the most important considerations when purchasing this accessory. Siemens identifies the 3RH1921-1XA22-0MA0 as a front-mounted auxiliary switch for specified 3RT1 contactors with sequence numbers 5–8.
The manufacturer documentation also identifies suitability for particular 3RT10, 3RT12, 3RT145, 3RT146, and 3RT147 configurations.
The block is designed for snap-on mounting. It should not be assumed compatible with every Siemens SIRIUS contactor simply because the products share the same brand or general product family.
Before installation, check:
- The complete contactor order number.
- The contactor frame size and sequence number.
- The front mounting arrangement.
- The required auxiliary contact configuration.
- The electrical ratings of the connected control circuit.
In particular, do not automatically apply this accessory to newer 3RT2 contactors. Siemens lists different auxiliary switch references for different contactor generations and mounting configurations.
Installation and Replacement Considerations
The 3RH1921-1XA22-0MA0 uses front snap-on mounting and screw terminals. Its installation requires both mechanical compatibility and correct electrical connection.
During replacement, technicians should verify the contactor’s front mounting interface and ensure the accessory is securely fitted. Terminal numbering should be checked against the wiring diagram before reconnecting the control circuit.
The specified conductor cross-section for auxiliary connections is 0.5–2.5 mm², subject to conductor type and preparation requirements.
The module has an IP20 front protection rating and is intended for installation within an appropriate electrical control enclosure. Its published operating temperature range is -25°C to +60°C.
What Should Buyers Check Before Ordering?
For maintenance and replacement projects, purchasing the correct auxiliary contact block requires more than matching the 2NO+2NC description.
Prepare the following information before requesting a quotation:
- Complete part number: 3RH1921-1XA22-0MA0.
- Existing Siemens contactor model.
- Contactor frame size and sequence number.
- Required contact arrangement.
- Terminal connection requirement.
- Purchase quantity and destination.
You can explore related automation components through the Siesource industrial automation catalogue. For model-specific sourcing enquiries, provide the contactor reference and required accessory configuration through the Siesource contact page.
Frequently Asked Questions
What is Siemens 3RH1921-1XA22-0MA0 used for?
It is a front-mounted auxiliary contact block used to expand the control contacts of compatible Siemens contactors. It provides two normally open and two normally closed contacts.
Does the 3RH1921-1XA22-0MA0 use screw terminals?
Yes. This version uses screw-type terminals. Siemens also offers a related spring-terminal version under a different order number.
What is the difference between 2NO and 2NC contacts?
Normally open contacts are open when the contactor is de-energized and close when it operates. Normally closed contacts behave in the opposite way.
Can this auxiliary block be installed on every Siemens 3RT contactor?
No. Compatibility depends on the contactor generation, frame size, sequence number, and mounting configuration. Check the Siemens compatibility documentation before installation.
What is the rated operational current at AC-15, 230 V?
The published AC-15 operational current is 6 A at 230 V. Other utilization categories and voltages have different ratings.
Conclusion
The Siemens 3RH1921-1XA22-0MA0 is a four-pole SIRIUS auxiliary contact block with 2 NO and 2 NC instantaneous contacts, screw terminals, and front snap-on mounting. Its primary role is to expand the control-circuit functionality of compatible 3RT1 contactors. Before selecting a replacement, verify the complete contactor reference, sequence number, mounting interface, and applicable AC-15 or DC-13 electrical ratings.