A copper run beside large factory motors shows noise on the pairs. The path cannot be moved, and the installed cable is unshielded. Which replacement addresses the noise?
Select an answer to reveal the explanation.
Short Explanation
Unshielded pairs next to a big motor are guitar strings next to a humbucker. You replace that run with shielded twisted pair, and you terminate and ground the shield so the noise has a path off the pairs. A plenum jacket, a shield that is not grounded, or a second unshielded cable in the same tray does not drain that noise.
Full Explanation
Motor noise couples into unshielded copper. The path cannot move, so the cable has to reject the noise in place. Shielded twisted pair helps when the shield is terminated and grounded, giving the noise a drain. Plenum rating is about the jacket in air-handling space. It does not add a shield. Copper with the drain wire left unconnected is the tempting twin because the foil is present. An unconnected drain does not carry the noise away and can make the run worse. A second unshielded run in the same tray sits in the same motors. Exam caveat: ground the shield the way the install standard specifies. A bond in the wrong place can create a loop. Operational check: after the shield is terminated and bonded, compare error counters with the motors running and confirm they stay flat. Bond the shield at the closet end the standard specifies, then recheck the counters with the motors still running. If the counters stay high, check that the shield is bonded and not merely present in the jacket. Leave the motors running during the retest so the noise is actually present.