How to Build a Noise-Resistant Control System: Wiring Matters More Than You Think

When it comes to building a stable and noise-resistant control system, wiring is one of the most critical—and often overlooked—factors. Even the best PLC or controller can behave unpredictably if the wiring layout is poorly designed.

Below are practical wiring guidelines commonly recommended by PLC manufacturers to reduce electrical noise and improve system reliability in control panels.

1) Use thick power cables and twist them
Use power lines that are as thick as practical and twist them together. Twisting helps reduce electromagnetic interference (EMI).

2) Keep transformer secondary wiring short and twisted
Twist the transformer secondary wiring and route it to the PLC using the shortest possible path to minimize noise pickup.

3) Always connect the ground on your SMPS
Do not leave the ground terminal of your switching power supply (SMPS) floating. Proper grounding improves stability and noise suppression.

4) Never mix AC and DC lines in the same wire duct
Route AC input/output lines separately from DC power and signal lines. Do not combine them in one duct.

5) Separate signal lines from power lines
Keep signal and power cables in separate ducts and maintain at least 20 cm (8 inches) of distance whenever possible.

6) Keep high-current devices away from the PLC
Place contactors, relays, breakers, and other high-current components as far from the PLC as possible.

7) Always operate components within their rated limits
Connect loads within the rated capacity of each component to reduce heat and prevent unexpected failures.

8) Manage heat inside the control panel
Install cooling fans and design airflow to exhaust hot air out of the enclosure, especially for summer conditions.

9) Maintain spacing between wire ducts and the PLC
Avoid mounting wire ducts too close to the PLC. Keep about 10–20 cm (4–8 inches) of space to reduce noise coupling and improve heat dissipation.

Most mysterious system failures are caused by noise, heat, and wiring layout issues rather than bad hardware.
Following these wiring practices can significantly improve the stability, reliability, and lifespan of your control system.