Background: the Industrial Control Panel and Power System

The customer designs industrial control panels for a production line. A typical cabinet includes several DIN-rail power systems feeding PLCs, I/O modules and sensors, plus a higher-power rack mount power supply that drives motors and actuators.

For this project, the panel needed to meet EMC requirements for industrial environments and ship with a full test report. Previous projects had passed EMC with some margin, but the new generation added more I/O and higher power loads, increasing EMC risk.

Instead of going directly to a third-party lab, the customer chose to run EMC pre-compliance testing in the TPS lab. The goal was to understand how the combination of DIN-rail power systems, the rack mount power supply and long field wiring would behave under EMC stress.

EMC Challenge: Emissions and Immunity Issues in the Cabinet

During the first exploratory measurements we saw several potential problems:

• Conducted emissions on the AC input of the cabinet, coming mainly from the rack mount power supply and its switching frequency harmonics.
• Radiated emissions at mid-range frequencies related to long I/O cables driven from the DIN-rail supplies.
• Immunity sensitivity on the PLC control system: fast transients on the mains and I/O caused random resets and occasional loss of communication.

None of these issues were unexpected for this kind of system, but if left unaddressed they would likely cause a failure at the formal EMC test for the industrial control panel.

TPS EMC Test Plan for the DIN-Rail and Rack-Mount System

Together with the customer we defined an EMC test plan focused on the real operating modes of the cabinet:

• Representative wiring. We built cable harnesses that matched the expected installation: long sensor and actuator lines, communication cables and mains supply, all routed similarly to the final control panel.
• Worst-case load conditions. The DIN-rail power systems and the rack mount power supply were loaded so that both the logic and the motor drives drew realistic currents.
• Relevant tests first. We prioritised conducted emissions on the cabinet mains input, radiated emissions in the frequency bands of concern and immunity tests such as EFT and surge on the AC input and key I/O lines.

This plan followed the same principles we describe in the EMC pre-compliance overview, but adapted to the specifics of industrial control panels and long field wiring.

Debug and Design Changes

Based on the pre-compliance results, we worked through a series of design improvements with the customer:

• Mains filtering and layout. The input filter for the rack mount power supply was adjusted and repositioned to reduce conducted emissions onto the cabinet mains.
• Cable routing and bonding. We changed the routing of some I/O bundles, improved the separation between noisy and sensitive lines and added a clearer bonding concept between DIN-rail, backplate and enclosure.
• PLC power and reset handling. Additional decoupling and a more robust reset strategy reduced the risk of PLC resets during EFT and surge tests.

Each change was verified in the TPS lab, so by the end of the session the customer had both improved EMC margins and a practical understanding of which changes mattered most.

Results and Lessons Learned

When the updated industrial control panel went to the third-party EMC lab, the results were straightforward:

• The cabinet passed EMC on the first formal attempt, with comfortable margins on the mains-input conducted emissions.
• Radiated emissions from the DIN-rail power systems and wiring stayed within limits in all tested configurations.
• The PLC and communication remained stable during immunity tests, with no unexpected resets or data loss.

Just as important, the customer documented the new grounding and wiring rules as a design guideline for future projects. The combination of pre-compliance testing and integration support reduced both risk and time-to-market for their next control panels.

How to Prepare a Similar Project for EMC Testing

If you are working on a cabinet that uses DIN-rail power systems, a rack mount power supply or a mix of both, you can prepare for EMC testing by collecting a few key points before contacting the TPS lab:

• A simplified diagram of the industrial control panel: mains input, power supplies, PLCs, I/O, communication links and major loads.
• Expected cable types and lengths, especially for field wiring that leaves the cabinet.
• Typical and worst-case operating modes for the DIN-rail and rack-mount power supplies.
• Any previous EMC experiences (good or bad) from similar cabinets in your company.

With this information we can propose a focused EMC test plan, schedule pre-compliance time in the lab and, if needed, coordinate with our integration solutions team to support cabinet design and wiring from an EMC perspective.

Book EMC Testing for a DIN-Rail / Rack-Mount System