Siemens 3RT2026-2BB40 Motor Control Unit with Double Auxiliary Contact 24VDC 25A 3NO

The Siemens 3RT2026-2BB40 motor control unit is a robust and reliable solution for demanding industrial applications. This 24VDC unit, rated at 25A and featuring 3 normally open (NO) auxiliary contacts, offers superior control and safety for electric motors. Its key advantages lie in its compact design, high switching capacity, and seamless integration into modern automation systems. The 3RT2026-2BB40 is engineered for superior performance and longevity, making it a prime choice for professionals seeking dependable motor management.

Product Specifications

| Feature               | Specification                                    |

| :-------------------- | :----------------------------------------------- |

| Manufacturer          | Siemens                                          |

| Product Type          | Motor Control Unit (Contactor)                   |

| Model Number          | 3RT2026-2BB40                                    |

| Coil Voltage          | 24VDC                                            |

| Rated Operational Current (AC-3, 400V) | 25 A                                             |

| Number of Auxiliary Contacts | 1 NO (built-in) + 1 NO (double auxiliary contact) |

| Pole Configuration    | 3-pole                                           |

| Mounting Type         | DIN rail or screw mounting                       |

| Terminal Type         | Spring-loaded terminals                          |

| Protection Class      | IP20                                             |

| Ambient Temperature   | -25°C to +60°C                                   |

Core Features & Market Positioning

The Siemens 3RT2026-2BB40 distinguishes itself through its innovative spring-loaded terminal technology, which ensures reliable connections even in environments subjected to significant vibration, a common challenge in industrial settings. This feature simplifies wiring and reduces maintenance requirements, positioning it as a superior choice over traditional screw terminals for critical applications. The inclusion of a double auxiliary contact (1 NO + 1 NO) offers enhanced flexibility for control and signaling circuits, allowing for more complex interlocking and monitoring functions without the need for additional components. Its compact SIRIUS design adheres to international standards, facilitating easy integration into control cabinets alongside other Siemens components and third-party devices, underscoring its versatility and market acceptance.

Key Application Scenarios

This motor control unit is ideally suited for a wide array of industrial automation tasks, particularly in sectors demanding precise and safe motor operation. It excels in controlling pumps, fans, compressors, and conveyor systems in manufacturing plants, process industries, and building automation. The 24VDC coil voltage makes it compatible with standard control voltages found in most PLC-based systems, simplifying integration for machine builders and system integrators. Its robust construction and high switching capacity ensure reliable performance in continuous operation scenarios, such as those found in material handling and HVAC systems, where motor starts and stops are frequent.

Practical System Integration Guidance

Integrating the Siemens 3RT2026-2BB40 into an existing control system is straightforward due to its standardized mounting and connection options. For DIN rail mounting, simply slide the unit onto the rail; for panel mounting, use the provided screw holes. The spring-loaded terminals accept solid and stranded conductors without requiring special tools, ensuring a secure and vibration-resistant connection. When connecting to a PLC, the 24VDC coil can be directly controlled by a PLC output module. The auxiliary contacts can be wired to PLC digital inputs for status feedback (e.g., contactor energized or de-energized) or for implementing safety interlocks within the control logic. It's crucial to ensure the control circuit wiring adheres to relevant safety standards, especially when used in safety-related applications.

Operation and Risk Mitigation

Proper operation of the 3RT2026-2BB40 involves ensuring the correct DC voltage is supplied to the coil terminals (A1 and A2) for activation. The main power terminals (L1, L2, L3 and T1, T2, T3) handle the motor power circuit. To mitigate risks, always de-energize the control and power circuits before performing any wiring or maintenance. Overloads should be protected by a suitable overload relay or via the motor protection functions integrated into advanced Sirius 3RT contactors, though this specific model relies on external protection devices. The IP20 protection class indicates it should be installed in an enclosure to prevent contact with live parts. Regular inspection of wiring connections for tightness is recommended to prevent electrical faults and ensure long-term operational safety.

Scalability & Long-Term Value

The Siemens 3RT2026-2BB40, as part of the broad SIRIUS innovation system, offers excellent scalability and long-term value. Its compatibility with other SIRIUS devices, such as overload relays, circuit breakers, and communication modules, allows for the creation of comprehensive motor control and protection solutions that can easily grow with evolving system requirements. Furthermore, its integration capabilities extend to modern Industrial Internet of Things (IIoT) platforms through optional accessories like communication gateways, enabling condition monitoring, predictive maintenance, and remote diagnostics. This forward-looking approach ensures that investments in the 3RT2026-2BB40 remain relevant and contribute to the efficiency and intelligence of industrial operations for years to come.

Frequently Asked Questions

1. What is the primary function of the Siemens 3RT2026-2BB40?

This unit serves as a vital component for controlling and switching electric motors in industrial settings. It provides a reliable means to start, stop, and protect motor loads safely and efficiently.

The 3RT2026-2BB40 is a contactor designed for direct control of motor circuits. Its 24VDC coil voltage makes it ideal for integration with modern control systems.

It also offers auxiliary contacts for signaling and interlocking purposes, enhancing the overall control system's functionality and safety.

2. Can I use the Siemens 3RT2026-2BB40 for AC motor control?

Yes, this contactor is rated for AC-3 duty, meaning it is suitable for controlling squirrel-cage motors and other AC induction motors.

The 3RT2026-2BB40 is designed to handle the specific switching requirements of AC motors, including the high inrush currents during startup.

Always ensure the motor's power rating and voltage match the contactor's specifications (e.g., 25A at 400V AC-3) for safe and effective operation.

3. What are the advantages of the spring-loaded terminals on this unit?

Spring-loaded terminals provide a vibration-resistant connection, crucial in industrial environments prone to shaking and movement. This reduces the risk of loose connections and ensures reliable electrical contact over time.

They simplify the wiring process as they often do not require special tools for conductor insertion, speeding up installation and maintenance.

This technology offers a more consistent and reliable connection compared to traditional screw terminals, particularly in applications where thermal cycling or vibration can cause screws to loosen.

4. How many auxiliary contacts does the Siemens 3RT2026-2BB40 have?

The Siemens 3RT2026-2BB40 comes with one built-in normally open (NO) auxiliary contact.

Additionally, it features a double auxiliary contact block, providing two more normally open (NO) contacts for enhanced control and signaling capabilities.

In total, this configuration provides three normally open auxiliary contacts, offering significant flexibility for interlocking, signaling, and monitoring circuits.

5. What is the correct way to wire the Siemens 3RT2026-2BB40?

Wire the 24VDC power supply to the coil terminals A1 and A2 to energize the contactor. Observe correct polarity if applicable for DC coils.

Connect the three-phase motor power supply to the main terminals L1, L2, and L3, and the motor leads to T1, T2, and T3.

Auxiliary contacts can be wired to PLC inputs or other control circuits as needed for signaling or interlocking functions.

6. What type of overload protection is recommended for this contactor?

The Siemens 3RT2026-2BB40 itself does not include an integrated overload relay; it is designed to be used in conjunction with separate overload relays.

Siemens offers a range of compatible overload relays (e.g., 3RU series) that can be mounted directly onto the contactor for a compact unit.

Alternatively, electronic overload relays or motor protection relays can be used in the control circuit to provide comprehensive motor protection against overcurrent and phase loss.

7. What is the significance of the "24VDC" coil voltage?

A 24VDC coil voltage is a common and safe standard in industrial automation, typically supplied by a PLC or a dedicated DC power supply.

This voltage level is considered SELV (Safety Extra-Low Voltage) in many standards, contributing to enhanced electrical safety during installation and maintenance.

Using 24VDC allows for direct interfacing with most modern programmable logic controllers (PLCs) without the need for complex voltage conversion or isolation circuits.

8. Can this unit be used in hazardous environments?

The standard Siemens 3RT2026-2BB40 is designed for general industrial use and has an IP20 rating, meaning it is protected against solid objects larger than 12.5mm but not against water.

For hazardous environments (e.g., explosive atmospheres), specialized versions or enclosures would be required to meet specific safety certifications and protection requirements.

Always consult the product's detailed technical documentation and relevant safety standards for suitability in specialized or hazardous environments.

9. What is the maximum switching capacity of the Siemens 3RT2026-2BB40?

The contactor is rated for 25A at 400V AC-3 duty, which represents its capability for controlling motor loads.

This rating indicates it can reliably switch motor currents, including the higher inrush currents encountered during motor start-up under specified conditions.

It's essential to consult the full technical datasheet for specific switching capacities under different voltage and current categories (e.g., AC-1, AC-3, DC-1) to ensure proper application.

10. How does the Siemens 3RT2026-2BB40 integrate with Siemens S7 PLCs?

The 3RT2026-2BB40 can be controlled directly by the digital outputs of a Siemens S7 PLC, provided the output module can supply the 24VDC coil voltage and sufficient current.

The auxiliary contacts can be wired to the digital inputs of the S7 PLC to provide status feedback on the contactor's operational state.

For more advanced integration, including diagnostics and parameterization, communication modules can be added to the SIRIUS system, allowing for data exchange with the S7 PLC over industrial networks like PROFINET or PROFIBUS.