What is the role of shielding in field wiring, and how is grounding typically applied?

• A. Shielding is irrelevant.
• B. Shielding must always be connected to V+.
• C. Shielding reduces electromagnetic interference; grounding/shielding depends on standards.
• D. Shielding should be left floating.

Answer: (C)

Shielding in field wiring is about keeping external electromagnetic fields from disturbing the signal and limiting the cable’s own emissions. The shield acts as a conductive barrier around the signal conductors, and to do its job it needs to be tied to a reference potential so noise has somewhere to go. Grounding the shield provides a low-impedance path for that noise to flow to earth or equipment ground rather than coupling into the signal path. The exact way the shield and ground are connected isn’t fixed universal practice—it depends on standards and the specific system design. Some installations bond the shield to ground at a single point to minimize ground-loop currents, while others, especially in high-EMI environments, bond it at multiple points or at both ends when the grounding network is well controlled. The takeaway is that shielding reduces electromagnetic interference, and how you ground or terminate the shield is guided by applicable standards and system needs.