Which statement about shielding in copper cabling is most accurate?

• A. Shielding is always required
• B. Shielding has no effect on EMI
• C. Shielding is only for outdoor use
• D. Shielding is used to reduce EMI when EMI is significant or runs are near power lines and equipment

Answer: (D)

Shielding in copper cabling is used to reduce electromagnetic interference, but it isn’t always needed. It becomes important when EMI levels are significant or when cables run near sources of interference like power lines, motors, or heavy equipment. The shield provides a conductive barrier that helps keep EMI out of the signal path and can also prevent the cable from emitting interference. For shielding to work effectively, it must be properly grounded or terminated at the ends, which is why in clean, low-EMI environments unshielded twisted-pair is often used. Therefore, the most accurate statement is that shielding is used to reduce EMI when EMI is significant or runs near power lines and equipment.