Which statement describes the difference between shielded twisted pair (STP) and unshielded twisted pair (UTP) in control cables?

Which statement describes the difference between shielded twisted pair (STP) and unshielded twisted pair (UTP) in control cables?

• A. UTP has shielding around the pair to reduce EMI.
• B. STP has shielding around the pair to reduce EMI.
• C. STP uses more copper content; UTP uses less copper.
• D. UTP is always cheaper than STP.

Answer: (B)

Shielding is the key difference: shielded twisted pair has a metallic shield around the conductors to block external electromagnetic interference, while unshielded twisted pair has no shield. That shield helps maintain signal integrity in electrically noisy control environments because it reduces the amount of interference that can couple into the wires. Properly grounding the shield at one end is important to prevent ground loops and to maximize protection, though it adds installation complexity and cost. Because of that extra protection, shielded cables are often chosen in environments with a lot of EMI, while unshielded cables are cheaper and simpler to install when EMI isn’t a major issue. The other statements are not accurate: unshielded pair doesn’t have shielding; the shield’s presence isn’t about simply adding more copper content; and while unshielded is usually cheaper, it isn’t an absolute rule in every situation.

Shielding is the key difference: shielded twisted pair has a metallic shield around the conductors to block external electromagnetic interference, while unshielded twisted pair has no shield. That shield helps maintain signal integrity in electrically noisy control environments because it reduces the amount of interference that can couple into the wires. Properly grounding the shield at one end is important to prevent ground loops and to maximize protection, though it adds installation complexity and cost. Because of that extra protection, shielded cables are often chosen in environments with a lot of EMI, while unshielded cables are cheaper and simpler to install when EMI isn’t a major issue. The other statements are not accurate: unshielded pair doesn’t have shielding; the shield’s presence isn’t about simply adding more copper content; and while unshielded is usually cheaper, it isn’t an absolute rule in every situation.