Siemens 5SU9356-8CN40 High Current Earth Leakage & Overload Protector RCBO 40A 30mA 1P+N D

The Siemens 5SU9356-8CN40 is a sophisticated Residual Current Circuit Breaker with Overcurrent protection (RCBO) designed for robust electrical safety in demanding industrial and commercial environments. This 1P+N unit offers a 40A current rating and a sensitive 30mA earth leakage detection threshold, providing comprehensive protection against electric shock, fire hazards, and equipment damage. Its high breaking capacity ensures reliable performance even under fault conditions, making it a critical component for safeguarding sensitive electrical installations. The 5SU9356-8CN40 combines the functions of a miniature circuit breaker (MCB) and a residual current device (RCD) into a single, compact device, simplifying panel design and installation.

Siemens 5SU9356-8CN40 Product Specifications

| Feature                   | Specification                                    |

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

| Product Type              | RCBO (Residual Current Circuit Breaker w/ Overcurrent) |

| Manufacturer              | Siemens                                          |

| Model Number              | 5SU9356-8CN40                                    |

| Poles                     | 1P+N (1 Pole + Neutral)                          |

| Rated Current (In)        | 40A                                              |

| Rated Residual Operating Current (IΔn) | 30mA                                           |

| Rated Voltage (Un)        | 230/400V AC                                      |

| Breaking Capacity (Icn)   | 6kA                                              |

| Tripping Characteristic   | Type D                                           |

| Frequency                 | 50/60 Hz                                         |

| Terminal Type             | Screw Terminals                                  |

| Mounting Type             | DIN Rail (35mm)                                  |

| Ambient Temperature Range | -25°C to +45°C                                   |

| Protection Class          | IP20                                             |

Core Features & Market Positioning

The Siemens 5SU9356-8CN40 stands out in the competitive landscape due to its integrated functionality and robust build quality, hallmarks of the Siemens brand. It offers a D-curve tripping characteristic, which is essential for industrial applications where temporary, high inrush currents from motors or transformers are common. This D-curve prevents nuisance tripping while still providing rapid protection against dangerous earth faults and overloads. Its 6kA breaking capacity ensures that the device can safely interrupt fault currents, preventing cascading failures in more extensive electrical systems. This combination of advanced tripping, high breaking capacity, and reliable RCD functionality positions the 5SU9356-8CN40 as a premium solution for critical infrastructure and sensitive equipment protection, offering a superior level of safety and operational continuity compared to simpler overcurrent protection devices.

Key Application Scenarios

This RCBO is ideally suited for applications requiring a high degree of electrical safety and reliability, particularly in environments with significant inductive loads or where sensitive electronic equipment is present. Common scenarios include motor control circuits, HVAC systems, and the protection of power distribution boards in commercial buildings and industrial facilities. It is also crucial for protecting circuits supplying medical equipment in healthcare settings, where uninterrupted and safe power is paramount. The 40A rating makes it suitable for higher-current branch circuits, while the 30mA sensitivity addresses shock protection requirements across a broad range of applications, aligning with stringent international safety standards. Its integration of overload and earth leakage protection simplifies circuit breaker panel design and reduces the number of individual devices required.

Practical System Integration Guidance

Integrating the Siemens 5SU9356-8CN40 into an existing electrical system is straightforward due to its standard DIN rail mounting and terminal configurations. Ensure that the incoming power supply is de-energized before installation. The line (L) and neutral (N) conductors from the power source should be connected to the designated input terminals, typically marked with "L(in)" and "N(in)". The protected load conductors are then connected to the output terminals, "L(out)" and "N(out)". It is critical to maintain correct polarity and ensure all connections are securely tightened to prevent overheating and ensure reliable operation. For applications requiring multiple RCBOs, proper busbar connections or individual wiring schemes must be employed, adhering to local electrical codes and the specific requirements of the distribution panel.

Operation and Risk Mitigation

The Siemens 5SU9356-8CN40 operates by continuously monitoring the balance of current flowing through the live and neutral conductors. If an imbalance exceeding 30mA is detected, indicating current is leaking to earth (potentially through a person), the device rapidly trips, disconnecting the power. Simultaneously, it provides overcurrent protection against overloads and short circuits via its integrated MCB function, tripping at currents dictated by its Type D characteristic. To mitigate risks, ensure regular testing of the RCD function using the built-in test button (typically labeled 'T'). Perform this test monthly. In case of tripping, the cause must be identified and rectified before resetting the device. Never force the lever up if it has tripped due to a fault. Avoid overloading circuits beyond the 40A rating.

Scalability & Long-Term Value

The Siemens 5SU9356-8CN40 offers excellent long-term value through its compatibility with the broader Siemens SENTRON protection device portfolio. This allows for seamless integration into larger electrical distribution systems and facilitates future expansions or upgrades. While the 5SU9356-8CN40 itself is a fixed-specification device, its modular design and adherence to industry standards mean it can be easily replaced or supplemented with other Siemens components as system requirements evolve. Its robust construction is engineered for longevity, minimizing the need for frequent replacements and contributing to overall system reliability and reduced maintenance costs. Integration with digital monitoring solutions is typically achieved through upstream or downstream devices within the broader automation architecture.

Frequently Asked Questions (FAQs)

What is the breaking capacity of the Siemens 5SU9356-8CN40 RCBO?

The Siemens 5SU9356-8CN40 RCBO features a robust 6kA breaking capacity. This specification is critical for industrial applications where fault currents can be significant. It ensures the device can safely interrupt short circuits without sustaining damage.

What does '1P+N' mean for this RCBO?

"1P+N" indicates that the RCBO protects one live (phase) conductor and the neutral conductor. This provides comprehensive protection for single-phase circuits. It ensures both live and neutral are disconnected simultaneously during a fault.

Can the Siemens 5SU9356-8CN40 be used for DC circuits?

No, the Siemens 5SU9356-8CN40 is specifically designed for AC (Alternating Current) circuits only. Using it on DC circuits can lead to improper operation and safety hazards. Always verify the supply type before installation.

What is the tripping characteristic of the 5SU9356-8CN40?

This RCBO has a Type D tripping characteristic. This type is suitable for circuits with high inrush currents, such as those powering motors or transformers. It prevents nuisance tripping while still providing overload protection.

How sensitive is the earth leakage protection?

The device offers 30mA sensitivity for earth leakage detection. This level is considered appropriate for personal protection against electric shock. It trips quickly when a fault current to earth is detected.

What are the main advantages of using an RCBO over separate RCD and MCB?

An RCBO combines RCD and MCB functions into a single unit. This saves space in electrical panels and simplifies wiring. It also ensures both overload and earth leakage protection are always linked.

Is the Siemens 5SU9356-8CN40 suitable for residential use?

While it can be used residentially, its 40A rating and Type D characteristic are more commonly found in industrial or commercial settings. For standard residential circuits, lower amperage and Type B or C characteristics are often preferred.

How do I test the functionality of the 5SU9356-8CN40?

Most RCBOs, including this model, have a test button (often labeled 'T'). Pressing this button simulates an earth fault and should cause the device to trip. Regular testing ensures the earth leakage protection remains functional.

What is the operating temperature range for this device?

The Siemens 5SU9356-8CN40 operates within an ambient temperature range of -25°C to +45°C. Deviating significantly from this range can affect performance and lifespan. Ensure proper ventilation in enclosures.

Where is the best place to install this RCBO?

Install this RCBO in a main distribution board or sub-distribution panel. It is best used at the point of circuit origin to protect downstream wiring and loads. Ensure it is accessible for testing and maintenance.