Noise Countermeasures in Factories: Basics of Shielded Cables

Introduction Industrial environments generate significant electrical noise from motors, VFDs, welders, and power lines. Shielded cables are one of the most effective ways to protect sensitive signals. This article explains the fundamentals of shielding and how to apply it correctly.


1. Why Noise Is a Problem

Electrical noise causes:

  • Sensor malfunctions

  • Communication errors

  • PLC input instability

  • Downtime and troubleshooting costs

Sources include:

  • VFDs

  • Servo motors

  • Welding machines

  • High-current power cables


2. Types of Cable Shielding

Foil Shield (F/UTP, F/FTP)

  • Thin aluminum foil

  • Excellent for high-frequency noise

  • Common in Ethernet cables

  • Not ideal for continuous flexing

Braid Shield (S/UTP, S/FTP)

  • Copper braid

  • Strong mechanical durability

  • Good for low-frequency noise

  • Suitable for moving cables

Combination Shield (SF/UTP, SF/FTP)

  • Foil + braid

  • Best overall noise protection

  • Ideal for servo motors and robotics


3. Proper Grounding Is Critical

A shielded cable without proper grounding is ineffective.

Best practices:

  • Ground the shield at one end for signal cables

  • Ground at both ends for high-frequency noise (Ethernet, VFD)

  • Use 360° shield termination (not pigtails)

  • Avoid long drain wires


4. Routing Techniques to Reduce Noise

  • Separate power and signal cables

  • Cross power cables at 90 degrees

  • Avoid parallel runs with VFD cables

  • Use metal conduits for additional shielding


5. When to Use Shielded Cables

Use shielded cables for:

  • Encoders

  • Analog signals

  • Ethernet in noisy areas

  • Servo motors

  • Long-distance sensor wiring


Conclusion

Shielded cables are a powerful tool for reducing electrical noise in industrial environments. By selecting the right shielding type, grounding it correctly, and routing cables properly, factories can significantly improve system stability and reduce downtime.