What minimum shielding coverage percentage is recommended?

• A. 85%
• B. 70%
• C. 100%
• D. 90%

Answer: (A)

Shielding effectiveness depends on how much of the cable’s circumference is covered by a conducting shield. A minimum of 85% shielding coverage is recommended because braided shields and other common aircraft wiring protectors still have small gaps where interference can slip through; when at least 85% of the circumference is covered, those gaps are minimized, helping to shunt unwanted RF energy and maintain proper impedance along the line. If coverage drops to lower levels, those gaps become easier paths for EMI to couple into or out of the conductors, reducing shielding effectiveness. While 100% coverage would be ideal, practical terminations and connectors prevent that, and 90% may be used in many cases, but 85% is set as a reliable minimum for general use to ensure adequate protection across installations.