DIN rail is the backbone of an industrial control panel. Everything mounts to it, including PLCs, relays, terminal blocks, circuit breakers, and power supplies. Figure 1 shows a populated panel from the author’s workbench.
Key Takeaways
- Use 35 mm top hat rail (TS 35) unless a component datasheet specifies otherwise.
- Leave 1–2 in (25–50 mm) between the tallest component and the wire duct.
- Install end brackets to prevent modules from sliding off the rail.
- Deburr every cut rail to prevent wire damage and injuries.
- Do not assume DIN rail is grounded — bond it explicitly if grounding is required.
This article is part of the DigiKey Field Guide for Industrial Automation
Location: Integrate It → Panel Construction.
Difficulty: 
Engineer — difficulty levels explained
Author: Aaron Dahlen | MSEE | Senior Applications Engineer, DigiKey
Last update: 06 Mar 2026
Figure 1: Workbench image — populated DIN rail with end stop, power distribution block, and electronic circuit breaker.
DIN Rail Fundamental Facts
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Profile: Three profiles exist — top hat (Ω shape), C section, and G section. Top hat is the most common profile. The G and C sections are legacy and increasingly rare. As evidence, consider the DigiKey catalog, where 1576 out of 1986 offerings are top hat (as of 05 Mar 2026). The popularity of top hat DIN rail is reflected in the design of the Weidmüller TSLD 5 DIN rail cutter as shown in Figure 2. The DigiKey catalog data plus the tool’s structure strongly implies that deep (15 mm) and shallow (7.5 mm) top hat rails are the de facto standard.
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Material: Steel is used in most applications. Aluminum is also common. DigiKey also has a small offering of stainless, copper, and plastic rails.
Common DIN Rail Sizes
Common DIN rail sizes are cut by the Weidmüller tool. The slots moving right to left are identified as:
- TS 35/7.5 mm to EN 50022; t = 1.0 mm
- TS 35/15 mm to EN 50022; t = 1.5 mm
- TS 32 mm to EN 50035; t = 1.5 mm
- TS 15/5.5 mm to EN 50045; t = 1.0 mm
- Copper earth bars 10 mm x 3 mm
We interpret this data as:
- TS: It is a mounting rail (German Tragschiene).
- 35: It is 35 mm wide.
- 7.5: It is 7.5 mm deep.
- t = 1.0: The material thickness is 1.0 mm.
Note: Standards such as EN 50022 have been superseded by IEC 60715.
35 mm Top Hat as the De Facto Standard
In practical terms, 35 mm top hat is the de facto standard. Almost everything sold for panel mounting assumes 35 mm DIN rail. It is the default unless the component datasheet says otherwise.
Figure 2: Image of the Weidmüller TSLD 5 DIN rail cutting tool.
Module Width — Planning Your Rail
Contrary to expectation, DIN-rail-mounted modules do not have a standard width. An example is shown in Figure 3. From left to right, the module widths are 17.7, 12.4, and 14.9 mm. The PLC shown in Figure 1 is 130 mm.
DIN rail length is a prime constraint in panel construction. Those little modules add up quickly. As a rule, crowded panels are difficult to construct and maintain. They make future modifications difficult.
Figure 3: Each module in this image has a different width.
Plan to include end brackets
End brackets prevent components from sliding off the ends. They are not optional, especially in high vibration environments — a relay that walks off the end of a rail at 3 AM is a real failure mode. They are also important for small student (trainer) projects: a small PLC could be destroyed if it falls off the rail. An example of an end bracket is the Weidmüller AEB 35 SC/1 as shown in Figure 4.
Clearance
Leave enough space below and above the rail for wire routing. This clearance depends on the components to be mounted to the rail as well as the wire duct clearance. The relative size of these components is shown in Figure 1. As a rule of thumb, leave an inch or two between the tallest component and the wire duct.
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Too compact and wire management becomes a problem during installation and a nightmare during troubleshooting.
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Too spread out and the wiring looks sloppy. The large unsupported spans are also susceptible to vibration. Finally, it adds cost, as the panel may be oversized for the application—with the understanding that we should leave some room for expansion. After all, industrial equipment has a lifetime measured in decades. A system integrator may need to replace the PLC decades later.
Note: there may also be thermal considerations. Be sure to consult the datasheet for recommended top to bottom and side to side clearance.
Figure 4: Workbench image — rail mounted to backplate, end brackets installed, wire routing space visible.
Standard Lengths and Custom Options
Some suppliers offer DIN rail in “standard” lengths such as 1 or 2 meters. DigiKey offers a variety of pre-cut lengths, saving you the time and effort of cutting the rail yourself. For example, if you are looking for a 20-inch length, DigiKey has 30 variations for your consideration.
How to cut it yourself
A hacksaw works. A cold cut chop saw is faster and cleaner. An angle grinder works in a pinch but leaves a rough edge that will cut your hand and snag wire later. Here, snag implies damaged insulation. It’s a latent failure that may show immediately or many years later as a short circuit.
Cut it, deburr it. That step is not optional — a sharp edge on the end of a rail will find your wrist eventually.
DIN Rail Is not Structural
DIN Rail does not “float” — it mounts to a steel backplate using screws through the slot in the rail base. The backplate carries the load. Overloading a rail that is only clipped at the ends will bow it and components will start to work loose.
DIN rail is available in slotted and unslotted formats. Heavy loads such as motor starters may benefit from using an unslotted TS 35/15 mm to EN 50022; t = 1.5 mm such as this Phoenix Contact 1201714. The installer would drill and place bolts spaced appropriately for the given load. This assumes the backing plate has the strength and appropriate mounting for the given load.
The ships I sailed on were especially hard on control panels from a vibration perspective. However, watch out, as even stationary panels must survive transport to the job site.
DIN Rail is Not Ground
It is tempting to use DIN rail as a system ground. After all, it’s steel, it runs the length of the panel, everything touches it. But unless you deliberately bond it to ground with a proper ground lug it is electrically floating.
Ground distribution in industrial panels is beyond the scope of this article. However, let me point to the Siemens ET 200SP as a target to expand your learning.
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Figure 5 shows the ground springs for an ET 200SP base unit. These will make electrical contact with the DIN rail.
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Figure 6 shows the grounding for a representative panel. Note that a distinct wire is used to connect the DIN rail to the grounding busbar. A wire also connects to the cable shields for analog modules. Terminal blocks specifically designed to connect a wire to the DIN rail (bite into the rail) are available. An example is the Weidmüller 2674560000. These grounding blocks are easy to identify, as their bodies are constructed using a swirled green / yellow plastic.
Taken together, these images show that grounding is a complex topic involving both power and analog signals. Go talk to an experienced controls engineer, I’ll bet they have a story to tell about chasing a ground loop only to discover that some part of the system was improperly grounded.
It’s helpful to think of a control panel as a really big printed circuit board. Many of the tricks-of-the-trade for grounding cross over. As an example, consider this experiment I performed to simulate ground loops within a control panel. A simple loop of wire was enough to cause interference strong enough to reset the test equipment I was using to measure the EMI.
DO NOT rely on the metal backplate to establish a ground connection.
Figure 5: Image of the ground connection for a Siemens ET 200 SP base unit.
Figure 6: Ground wire connections for a Siemens ET 200SP system.
Continue Exploring Industrial Control Systems
If this discussion was helpful, you may also want to explore:
DigiKey Navigation
- Full Catalog: Industrial Control & Automation
- Featured Hardware: DIN Rail
- Essential Accessories: Terminal Blocks
Related Foundational Articles
Mount your hardware
Protect your circuits
Switch your signals — Relays
Start your motors — Motor Starters
Power your system — 24 VDC Supply
About This Author
Aaron Dahlen, LCDR USCG (Ret.), is a Senior Applications Engineer at DigiKey in Thief River Falls. His background in electronics and industrial automation was shaped by a 27-year military career as both technician and engineer, followed by over a decade of teaching.
Dahlen holds an MSEE from Minnesota State University, Mankato. He has taught in an ABET-accredited electrical engineering program, served as coordinator of an electronic engineering technology program, and instructed military technicians in component-level repair.
Today, he has returned to his home in northern Minnesota, completing a decades-long journey that began with a search for capacitors. Read his story here.