First Steps for DIN Rail Hardware

What is DIN rail?

DIN rail is to industrial controls as the breadboard is to electronics. Both serve as a mounting base allowing fast construction of circuits. Both systems accommodate a large number and variety of electrical components. The difference is that DIN rail constructed circuits are robust and designed for full deployment in harsh industrial environments. This includes factory setting and even high vibration shipboard environments. Breadboard circuits are generally reserved for prototyping electrical circuits.

This brief is focused on the DIN rail components such as the Programmable Logic Controller (PLC) and control relay as shown in Figure 1. We will explore the orientation and techniques to snap components into position. In this example, we see an Arduino Opta PLC next to a Finder relay, socket, and diode module.

Figure 1: Proper orientation of a PLC and relay. The quick release mechanisms, located at the bottom of each device, have been circled.

What is the design philosophy for industrial control systems that supports DIN rail construction?

The term DIN points to a standard. In fact, the German acronym itself contains the terms standardization as in “Deutsches Institut für Normung” (DIN). The English translation is “German Institute for Standardization.”

In this application, the standard is focused on the problem of physically mounting devices to a steel or aluminum rail. The standardized rail method allows devices to be quickly installed, replaced, and rearranged. Most devices are clipped into the rail. The standard describes the physical dimensions and functional requirements and related requirements such as forces that may be applied to the rail.

Tech Tip: Flexibility and speed of installation are an essential aspect of the DIN system. We cannot overstress the importance of speed especially when we consider the time it takes to restore equipment to proper operation. Always remember that equipment down time is extraordinarily expensive. Proactive equipment design with DIN rail components can significantly impact your bottom line.

This focus on standards is the perfect way to think about DIN rail components. Here the IEC 60715 global standard encompasses a large collection of low voltage switchgear and controllergear components that are designed to work together in your industrial control panel. Rather than being restricted to a specific manufacturer’s proprietary design, the IEC standard encompasses components from many manufacturers with high confidence that they will work together. For example, there are dozens of closely related relays that could be substituted for the one shown in Figure 1. As a designer you are free to choose your preferred options from your preferred manufacturer to meet your specific needs. In all cases we can be confident of the interoperability of the DIN rail mounting.

Tech Tip: There are different types of DIN rail. The most common type is “Top Hat” as featured in this article. Occasionally you will encounter “C section” and “G section.” The terms Top Hat, C, and G refer to the general shape of the rail when viewed from the side. With a bit of imagination, we can see the silhouette of the top hat and the letters C and G.

Do DIN rail components have a direction / orientation?

Physical orientation is one of the first challenges you will encounter with DIN rail mounted components. There is an implicit “this way up” orientation that must be understood and adhered to. As an example, consider Figure 1. The large red up arrow shows the proper orientation of the components. Notice that the text on the PLC face is naturally orientated in the up direction while the text on the finder relay is sideways. A more important indication is the circled clip release mechanism shown in the lower part of the picture.

Figure 2 shows the mechanism from the back. Here the spring-loaded clip mechanism for the relay is clearly visible. A similar mechanism is hidden inside the body of the PLC.

Figure 3 shows yet another way to think about component orientation. Here we see the quick release mechanism in action. A small screwdriver is used to release the tab allowing the component to be released from the DIN rail.

Tech Tip: DIN rail components are often mounted in a wall-mounted industrial control panel. The components are mounted so that the top of the DIN rail components hooks the upper part of the rail while the quick release snap engages the lower part of the rail. As a result, the quick release mechanism is located below the component as suggested by Figures 1 to 3.

Figure 2: View of the back side of the DIN mounted PLC and relay. The circle section identifies the relay’s quick release spring loaded mechanism. The PLC shares a similar clip mechanism however it is hidden inside the PLC body.

Figure 3: A screwdriver may be used to quickly remove a DIN rail mounted device by applying pressure to the release tab. This picture shows the relay in the process of being removed.

What are the grounding precautions for DIN rail components?

Close inspection of Figure 2 shows that the PLC and relay are electrically isolated from the DIN rail via plastic connections. This is perfectly acceptable for many components. However, there are DIN rail components specifically designed for line-powered devices that require solid grounding. This is a critical safety consideration to prevent electrical shock. As a general statement all exposed metal surfaces must share a common safety ground.

A representative Phoenix Contact ground module terminal block is shown in Figure 4. Close inspection reveals that the internal bus connection is tied to a metallic spring. When installed, this spring will make a low resistance connection with the steel or aluminum DIN rail.

A full description of control panel grounding and bonding is beyond the scope of this article. For additional information please refer to UL 508A Standard. The link will bring you to a training page to get you started with certified panel shop.

Figure 4: Picture of a ground module terminal block. The prominent metal spring provides a low resistance connection to the DIN rail.

Conclusion

This engineering brief serves as an introduction to DIN rail components. It provides a first look at the DIN rail standard and offer tips to get you started. By now you should have a clear understanding of up vs down in a control panel.

Be sure to test your knowledge by answering the questions located at the end of this note. Also, please leave your comments and suggestions in the space below.

Best Wishes,

APDahlen

Return to the Industrial Control and Automation Index.

About the author

Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this. LinkedIn | Aaron Dahlen - Application Engineer - DigiKey

Questions:

  1. T/F: A DIN rail mounted component clips into the top of the rail and snaps into the lower.

  2. T/F: The physical orientation of a DIN rail component may be strictly determined by the components text.

  3. T/F: The DIN rail standard included torque specification for the PLC’s wire terminals.

  4. T/F: The screw clamp for the DIN rail end-stop as shown in Figure 4 would face down.

  5. Sketch cross sections of Top Hat, C, and G DIN rail.

  6. Define the term “standard” as applied to DIN rail.

  7. Define the term “interoperability” as applied to DIN rail.

  8. Suppose a DIN rail mounted component is hooked but not clipped into the rail. How would you locate this improper installation? For full credit, describe the motion you would use to detect the anomaly.

  9. What is the significance of a green or green/yellow stripe colored terminal block? Research the significance and precautions taken with these unique devices.

Figure 4: Picture of a DIN rail end stop.

Critical thinking questions:

  1. Identify and describe at least three additional standards that may be encountered in an industrial control panel. For full credit, include at least one safety standard.

  2. Speculate as to why Top Hat has gained popularity.

  3. What precautions should be taken to ground DIN rail and DIN rail mounted components?

  4. Research and then describe the physical limitation of a single DIN rail when used for Variable Frequency Drives (VFD). Specifically, what is the DIN rail limitation in terms of drive horsepower?

  5. DIN rail is occasionally mounted vertically in a control panel. Look online for examples to determine what panel builders describe as “up”.