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Siemens 3RH2131-2BB40 Specs: 24V DC Contactor Relay Guide
The Siemens 3RH2131-2BB40 is a SIRIUS 3RH2 contactor relay with three normally open (3 NO) and one normally closed (1 NC) auxiliary contacts, a 24V DC coil, and spring-loaded terminals. It uses an S00 frame and is designed for switching control signals in industrial control circuits rather than directly switching motor power loads. Its key selection factors include contact configuration, DC coil compatibility, switching duty, and terminal requirements.
Siemens 3RH2131-2BB40 Technical Specifications
The 3RH2131-2BB40 belongs to Siemens’ SIRIUS auxiliary contactor range. Its four-pole configuration provides three NO contacts and one NC contact for control logic, status signaling, and electrical interlocking.
| Specification | Details |
|---|---|
| Manufacturer | Siemens |
| Product family | SIRIUS 3RH2 |
| Complete model number | 3RH2131-2BB40 |
| Product type | Contactor relay / auxiliary contactor |
| Frame size | S00 |
| Contact configuration | 3 NO + 1 NC |
| Coil control voltage | 24V DC |
| Coil operating voltage factor | 0.8–1.1 × rated control voltage |
| Coil power consumption | 4 W typical |
| Terminal connection | Spring-loaded terminals |
| Rated insulation voltage | 690 V |
| Rated impulse withstand voltage | 6 kV |
| AC-15 operational current | 10 A at 230 V; 3 A at 400 V |
| DC-13 operational current | 10 A at 24 V with one current path |
| Mechanical service life | 30 million operating cycles, typical |
| Front protection rating | IP20 |
| Operating temperature | -25°C to +60°C |
| Dimensions (W × H × D) | 45 × 70 × 73 mm |
| Net weight | Approximately 286 g |
Source: Siemens official 3RH2131-2BB40 datasheet and Siemens Industry Mall. Electrical ratings depend on the utilization category and operating conditions.
How Does the 3RH2131-2BB40 Work?
The 3RH2131-2BB40 operates through an electromagnetic coil. When the 24V DC control supply energizes the coil, the internal armature moves and changes the state of its four auxiliary contacts.
The contact arrangement provides:
- Three normally open contacts: Close when the relay is energized.
- One normally closed contact: Opens when the relay is energized.
This arrangement allows one control command to operate several circuit paths. For example, an NO contact can activate a downstream control circuit while the NC contact changes the state of an interlocking or status circuit.
The device is therefore useful when control systems need multiple switching signals from one electromagnetic operating mechanism.
Understanding the 3 NO + 1 NC Contact Configuration
Contact configuration is often more important than the physical appearance of a contactor relay when selecting a replacement.
Consider a machine control panel that requires three separate NO switching paths and one NC feedback path. The 3RH2131-2BB40 can provide this arrangement without requiring an additional basic auxiliary contact block for those four contact paths.
However, engineers must distinguish between contact availability and contact electrical ratings. The maximum permissible current depends on the utilization category and voltage.
| Utilization category | Rated voltage | Operational current |
|---|---|---|
| AC-15 | 230 V | 10 A |
| AC-15 | 400 V | 3 A |
| DC-13, one current path | 24 V | 10 A |
| DC-13, one current path | 110 V | 1 A |
| DC-13, one current path | 220 V | 0.3 A |
For DC applications, Siemens also specifies different permissible currents when two or three contact paths are connected in series. These values must be taken from the relevant datasheet rather than assumed to be the same as single-contact ratings.
Why 24V DC Coil Compatibility Matters
The 3RH2131-2BB40 uses a 24V DC electromagnetic coil. Siemens specifies a control supply voltage operating factor of 0.8–1.1, corresponding to an approximate 19.2–26.4 V DC operating range around the rated voltage.
This matters when the relay is controlled by a PLC output or an industrial DC power supply. Voltage drop across long wiring runs, supply fluctuations, and shared loads can affect the actual voltage available at the coil.
The coil has a typical power consumption of 4 W. When calculating the control power budget, engineers should consider the number of simultaneously energized contactors and the capacity of the DC power supply.
Spring-Loaded Terminals and Installation Considerations
Unlike screw-terminal versions of the SIRIUS 3RH2 range, the 3RH2131-2BB40 uses spring-loaded connections. This terminal design is relevant in control cabinets where wiring speed, conductor preparation, and resistance to loosening under vibration are important.
Key installation considerations include:
- Use conductors within the manufacturer’s specified cross-section range.
- Follow the required wire preparation and insertion procedure.
- Identify the coil terminals A1 and A2 correctly.
- Verify the NO and NC contact terminal numbering against the wiring diagram.
- Allow the specified installation clearances and use the approved mounting arrangement.
The device measures approximately 45 mm wide, 70 mm high, and 73 mm deep. These dimensions should be checked against the existing control cabinet layout before replacement.
Where Is the Siemens 3RH2131-2BB40 Used?
The contactor relay is suitable for industrial control applications that require multiple auxiliary switching paths rather than direct motor power switching.
- PLC control cabinets: Switching control signals between PLC outputs and downstream electrical circuits.
- Electrical interlocking: Using NO and NC contacts to coordinate operating states between control devices.
- Machine automation: Managing auxiliary commands for production equipment.
- Status signaling: Providing switching paths for indication and control logic.
- Industrial equipment: Supporting auxiliary control circuits in pumps, conveyors, and processing machinery.
For applications involving actual motor power switching, a dedicated power contactor should be selected according to the motor rating and utilization category. The Siemens 3RT6023-1AN20 power contactor is an example of a related SIRIUS power switching product, not a direct replacement for this auxiliary relay.
3RH2131-2BB40 Replacement: What Should Engineers Check?
When replacing an existing contactor relay, matching the 24V DC coil voltage is not sufficient. The contact arrangement, electrical ratings, and connection method must also match the application.
- Verify the contact arrangement: Confirm that the control circuit requires 3 NO and 1 NC.
- Check the coil voltage: Confirm that the existing control supply is suitable for 24V DC operation.
- Compare terminal types: A spring-loaded version is not automatically interchangeable with a screw-terminal version.
- Review contact utilization: Check AC-15 or DC-13 ratings according to the actual load.
- Confirm dimensions and mounting: Check the S00 frame and existing DIN-rail installation.
- Review the wiring diagram: Confirm terminal assignments before reconnecting control circuits.
For a related Siemens relay model used in railway control applications, see the Siemens 3RH2140-2XF40-0LA2 contactor relay guide. That model has a different contact configuration and coil specification, so it should not be considered a direct substitute.
You can also explore the Siesource industrial automation product catalogue for related Siemens control components. When requesting a quotation, provide the complete part number, quantity, existing control voltage, and required product condition.
Frequently Asked Questions
What is Siemens 3RH2131-2BB40 used for?
It is a 24V DC SIRIUS contactor relay used for switching auxiliary control signals. It provides three normally open contacts and one normally closed contact.
What is the contact configuration of 3RH2131-2BB40?
The relay has three NO contacts and one NC contact, providing four switching paths for industrial control applications.
Does the 3RH2131-2BB40 use screw or spring terminals?
It uses spring-loaded terminals for its control and auxiliary circuits. Check the conductor requirements in the Siemens installation documentation.
Can the 3RH2131-2BB40 switch a motor directly?
It is an auxiliary contactor relay intended for control circuits, not a substitute for a suitably rated power contactor used to switch motor loads.
What is the operating temperature range?
The specified operating ambient temperature range is -25°C to +60°C. Storage conditions are different and should be checked separately.
Conclusion
The Siemens 3RH2131-2BB40 is a compact SIRIUS auxiliary contactor with a 24V DC coil, 3 NO + 1 NC contacts, and spring-loaded terminals. Its main value lies in providing multiple control switching paths within industrial automation panels. Before selecting a replacement, verify coil voltage, contact utilization ratings, terminal construction, and mounting dimensions against the original circuit requirements.