Under what circumstances might shielded twisted pair (STP) be preferred over unshielded twisted pair (UTP)?

• A. Because STP reduces electromagnetic interference (EMI) in environments with significant EMI.
• B. Because STP is universally cheaper.
• C. Because STP is lighter and more flexible in all cases.
• D. Because STP never requires grounding.

Answer: (B)

Shielded twisted pair is chosen when electromagnetic interference is a real concern. The shield provides a conductive barrier around the conductors and, when properly grounded, gives EMI currents a low-impedance path to ground. This helps prevent external noise from coupling into the signal and also reduces the noise that the cable itself might radiate. That advantage is most noticeable in environments with significant EMI, long cable runs near noise sources, or around power equipment.

Keep in mind that shielding adds cost, weight, and stiffness, and the shield must be grounded correctly to be effective. If grounding is mishandled, the shield can even worsen noise instead of reducing it. This is why the other statements aren’t the best reasons to choose STP: it isn’t universally cheaper, it isn’t lighter or more flexible in all cases, and shielding isn’t inherently free of grounding requirements.