DIN rails in industrial automation: supporting PLCs, relays and contactors

DIN rails are one of the most familiar components in industrial control panels, and one of the most underestimated.

Often treated as a simple mounting solution, DIN rails actually play a critical role in how reliably PLCs, relays, contactors and other control devices perform over time. Decisions around rail type, material, layout and installation directly affect panel integrity, maintainability and long-term system uptime.

This article goes beyond basic definitions to explore how DIN rails support real-world automation systems, and what engineers should consider to get the most from them.

More than a mounting rail

At a glance, a DIN rail’s job seems straightforward: provide a standardised way to mount electrical and automation components inside an enclosure.

In practice, DIN rails also:

• Define how components are physically supported and aligned
• Influence vibration transmission and mechanical stress
• Shape wiring routes, accessibility, and serviceability
• Affect how easily systems can be expanded or modified

When DIN rails are poorly chosen or installed as an afterthought, the consequences tend to surface later, during commissioning, maintenance or fault-finding, when changes are most expensive.

What a DIN rail actually does in a control panel

A DIN rail provides a mechanical backbone for automation components. It ensures consistent positioning, enables modular assembly and allows devices to be installed or replaced without major rework.

Importantly, DIN rails are not designed to carry electrical load in the way busbars do. While they may be bonded to earth or chassis ground, their primary role is structural. Confusing these roles can lead to unsafe assumptions during panel design.

Understanding the mechanical nature of DIN rails is key to using them effectively.

DIN rail profiles and materials: why the details matter

The 35 mm “top-hat” DIN rail (TS35) is the most widely used profile in industrial automation, but it’s not the only option, nor always the best one for every application.

Common profiles include:

• TS35 (35 mm) - the standard choice for PLCs, terminal blocks, relays, and most control devices
• TS15 (15 mm) - used where space is extremely limited
• G-type rails – occasionally used for heavier components

Material selection also matters:

• Zinc-plated steel offers good strength and cost-effectiveness for most panels
• Stainless steel is preferred in corrosive or hygienic environments
• Aluminium reduces weight but may sacrifice rigidity

For PLCs and densely populated I/O racks, rail rigidity and straightness are especially important. Flexing rails can introduce stress into module housings and connectors, particularly in vibration-prone environments.

Supporting PLCs: stability, alignment and accessibility

PLCs are often the most sensitive devices in a control panel. Although they snap neatly onto DIN rails, their long-term reliability depends on how well that rail supports them.

Key considerations include:

• Rail straightness and support spacing to prevent module misalignment
• Vibration control, especially in machinery or mobile applications
• Thermal considerations, ensuring airflow around PLC racks
• Accessibility, allowing modules to be removed or added without disturbing adjacent wiring

Mounting PLCs on a rigid, well-supported DIN rail, positioned logically within the panel, reduces connector fatigue and makes maintenance safer and faster.

Relays and contactors: load and layout considerations

Relays and contactors place different demands on DIN rails compared to PLCs.

These devices can be:

• Heavier
• Subject to mechanical shock during operation
• Wired with larger, stiffer conductors

If rails are underspecified or poorly supported, they may flex or loosen over time, affecting both mechanical stability and wiring integrity.

Good practice includes:

• Providing adequate end stops to prevent component movement
• Allowing sufficient spacing for heat dissipation
• Separating high-power switching devices from sensitive control electronics

The rail itself becomes part of the system’s mechanical resilience.

Top brands in relays and contactors

DIN rail layout: designing for humans, not just hardware

One of the most overlooked aspects of DIN rail use is panel layout.

Experienced engineers design layouts that support:

• Logical grouping of functions (power, control, I/O)
• Clear wiring routes with minimal crossing
• Easy identification and replacement of components

A well-planned DIN rail layout reduces wiring errors, speeds up commissioning and dramatically improves fault-finding later in the system’s life.

DIN rails don’t just hold components - they define how people interact with the system.

Installation quality: where good designs can fail

Even the best DIN rail selection can be undermined by poor installation.

Common issues include:

• Rails cut inaccurately, causing misalignment
• Insufficient fixing points leading to vibration
• Inconsistent mounting torque on fasteners
• Burrs or sharp edges damaging cables during installation

Attention to these details may seem minor, but they have an outsized impact on long-term reliability.

Maintenance and lifecycle considerations

Industrial automation systems evolve. New sensors are added, PLC modules are upgraded, and control strategies change.

DIN rails that support this evolution tend to:

• Have spare capacity for expansion
• Use standardised components across panels or sites
• Allow individual devices to be replaced without disturbing others

From a maintenance perspective, a well-designed DIN rail system reduces downtime and lowers the risk of introducing new faults during modifications.

Common mistakes engineers should avoid

Across many installations, the same mistakes appear repeatedly:

• Selecting DIN rails purely on cost
• Ignoring mechanical load and vibration
• Overcrowding rails with no room for growth
• Treating layout as an aesthetic concern rather than a functional one

These decisions rarely cause immediate problems, which is why they persist, but they often limit system performance later on.

DIN rails as a foundation of automation reliability

DIN rails may be one of the simplest components in an automation system, but their influence is far-reaching.

When chosen thoughtfully and installed correctly, they provide a stable, modular foundation for PLCs, relays, contactors and other control devices. They improve maintainability, support future expansion and contribute quietly but significantly to system reliability.

In industrial automation, success is often determined not by the most advanced technology, but by how well the fundamentals are executed. DIN rails are one of those fundamentals worth getting right.