Core Construction: How a Shielded Cable is Built
Understanding a shielded cable starts with its layered structure:
Conductor & Insulation: Like any standard cable, the core consists of conductors (often stranded wires for flexibility) surrounded by an insulation layer. This carries the electrical signal or power.
The Shield – The Key Differentiator: This is the added protective layer. It typically comes in two forms:
Single Shield: A braided mesh of fine copper or aluminum wires, or a spiral-wound or longitudinal foil tape (usually aluminum). The shield works on the principles of the skin effect (where high-frequency currents flow on the conductor’s surface) and reflection, blocking external EMI.
Double/Foil + Braid Shield: For superior protection, especially against high-frequency interference, a combination shield is used. A foil layer provides 100% coverage, while an overbraid adds mechanical strength and better low-frequency protection.
Critical: Proper Grounding: The shield’s effectiveness hinges on correct grounding. It is typically grounded at one end only (single-point grounding) to prevent ground loops—circulating currents that can themselves become a source of noise. In complex systems like computer control networks, a centralized single-point ground is standard practice.
