Understanding the Differences: Safety PLC vs. Normal PLC in Siemens Automation

Key Takeaways

Safety PLCMeets specific safety standards (IEC 61508, IEC 61511), designed to fail safely, redundant hardware.
Normal PLCUsed for general automation, flexible and cost-effective, lacks built-in safety functions.
ComparisonSafety PLCs are essential for high-risk environments, while Normal PLCs are sufficient for less critical applications.
IntegrationCombining both types can enhance system safety through redundancy and advanced monitoring.
Future TrendsIntegration with IIoT and AI, increased cybersecurity measures, and wireless connectivity.


Programmable Logic Controllers (PLCs) are foundational to modern industrial automation. At ControlNexus, established in 2013 as a leader in providing Siemens PLCs, HMIs, and Inverters, we understand the critical importance of selecting the right type of PLC. Whether it’s for safety-critical applications or general automation, the choice between a Safety PLC and a Normal PLC can significantly impact the safety and efficiency of your operations.

What are Safety PLCs?

Safety PLCs are specialized controllers designed with the primary goal of enhancing safety in industrial environments. These systems adhere to rigorous safety standards, such as IEC 61508 and IEC 61511, ensuring they can handle critical safety functions reliably. Key features include:

  • Safety-Centric Design: Safety PLCs are engineered to execute safety-related tasks effectively. They can detect and react to hazardous conditions swiftly, mitigating risks to both machinery and personnel.
  • Redundancy and Fail-Safe Operations: These controllers are built to be fail-safe, meaning they maintain or enter a safe state during failures. Redundancy in processors and I/O modules ensures that backup systems take over if one fails, enhancing reliability.
  • Certified for Safety: With certifications from recognized third-party organizations, Safety PLCs guarantee adherence to international safety standards.

In environments where a failure could result in significant harm, such as chemical processing or oil and gas industries, Safety PLCs are indispensable.

What are Normal PLCs?

Normal or Standard PLCs are the workhorses of general industrial automation. Unlike their safety-oriented counterparts, these PLCs focus on controlling and automating day-to-day processes without the additional layers of safety-specific functionalities. Features include:

  • Versatile Applications: From controlling simple machines to managing complex automation tasks, Normal PLCs handle a wide range of functions across various industries.
  • Programming Flexibility: Typically programmed using ladder logic or similar languages, these PLCs offer flexibility to adapt to different operational needs.
  • Cost-Effectiveness: Without the specialized safety features, Normal PLCs are more budget-friendly and sufficient for applications where safety is not a critical concern.

For many standard applications in industries like manufacturing, packaging, and material handling, a Normal PLC is perfectly adequate.

Comparative Analysis of Safety and Normal PLCs

Understanding the specific needs of your application is crucial in choosing between a safe and a Normal PLC. Here are some comparative insights:

  • Safety Features: Safety PLCs come with built-in functions like emergency stop monitoring and safety door controls, which are absent in Normal PLCs.
  • Hardware Redundancy: Safety PLCs often feature dual or even triple redundant systems to ensure continuous operation, a rarity in Normal PLCs.
  • Cost vs. Safety: While Normal PLCs are more cost-effective, Safety PLCs are essential for high-risk scenarios where the extra expense is justified by the need for enhanced safety measures.

By assessing the operational environment and safety requirements, businesses can make informed decisions about which type of PLC best suits their needs.

The understanding of these PLCs not only ensures the appropriate level of automation but also safeguards the investments and, more importantly, the lives of those working in proximity to these machines. For more in-depth information on specific Siemens PLC models, consider visiting our detailed pages on Siemens S7-300 and Siemens S7-1500 PLCs.

Integration Strategies for Enhanced Safety

Integrating both Safety and Normal PLCs within a single system can offer an enhanced layer of protection, especially in complex industrial environments. By combining their capabilities, organizations can leverage the flexibility and robust control of Normal PLCs with the critical safety features of Safety PLCs. Here’s how they can work together:

  • Safety Interlocks: These can be managed by Safety PLCs to ensure that hazardous machinery cannot operate unless safe conditions are met, while Normal PLCs manage the broader system operations.
  • Emergency Stop Systems: Safety PLCs can handle emergency stop functionalities, immediately bringing systems to a safe state, while Normal PLCs can resume operations once safety checks are completed.
  • Redundancy: Utilizing both PLC types in a redundant configuration allows for failover capabilities, where the Normal PLC can continue operations if the Safety PLC detects a fault and vice versa, ensuring no downtime and maintaining safety.

The landscape of PLC technology is rapidly evolving, influenced by major advancements in automation and computing. Here are some future trends that are shaping the use of PLCs:

  • Industrial Internet of Things (IIoT): Integration with IIoT platforms allows PLCs to communicate with a wider network of devices, enhancing data collection and enabling smarter, data-driven decisions.
  • Artificial Intelligence (AI) and Machine Learning (ML): These technologies are beginning to be integrated into PLC systems, providing the ability to predict failures before they happen and optimize system operations for efficiency and safety.
  • Cybersecurity: As PLCs become more interconnected, securing these systems against cyber threats is becoming critical. Future PLCs will need to incorporate advanced cybersecurity measures to protect critical industrial infrastructure.
  • Wireless Connectivity: The adoption of wireless communication standards such as Wi-Fi and Bluetooth enhances the flexibility and installation options of PLC systems in industrial environments.
  • Edge Computing: This technology allows for real-time data processing close to the source of data collection, reducing latency and improving response times in critical applications.

These advancements not only enhance the functionality and efficiency of PLC systems but also ensure they are adaptable to future industrial needs.

Choosing the Right PLC for Your Needs

Selecting the right type of PLC for your industrial application is crucial for optimizing both performance and safety. Consider the following factors:

  • Assess the Risk: Evaluate the potential risks involved in the application. High-risk environments may necessitate the use of Safety PLCs.
  • Cost vs. Benefit: Consider the cost implications of implementing a Safety PLC against the potential risks of not doing so.
  • Future Scalability: Ensure that the PLC system is scalable and can adapt to future technological advances and expansions in your facility.

Making the right choice involves understanding the specific requirements of your application and the capabilities of different PLC types. At ControlNexus, we provide expert guidance and a wide range of Siemens PLC solutions to meet your automation needs. Explore our extensive lineup from Siemens S7-200 for compact solutions to advanced Siemens S7-1500 series for more demanding applications.


Understanding the differences between Safety and Normal PLCs is essential for implementing effective industrial automation solutions. With advancements in technology, the capabilities of PLCs continue to evolve, making them even more integral to industrial operations. By carefully selecting the right type of PLC, you can ensure not only the efficiency and productivity of your processes but also the safety and reliability of your automation system.

For further information and to explore our range of Siemens PLCs, visit ControlNexus.


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