RCDD Question #318: Real Exam Question with Answer & Explanation

The correct answer is D. STP. When two locations have different ground potentials (a ground loop condition), any cable whose shield is bonded to ground at both ends will carry current between those two grounds. STP (Shielded Twisted Pair) has a metallic shield that is grounded at both ends; the 2.1 V rms pote

Question

You must place a cable between 2 equipment locations with separate grounds having a potential difference between them of 2.1 V rms. Which one of the following cables should NOT be used?

Options

AMultimode
BSinglemode
CUTP
DSTP

Explanation

When two locations have different ground potentials (a ground loop condition), any cable whose shield is bonded to ground at both ends will carry current between those two grounds. STP (Shielded Twisted Pair) has a metallic shield that is grounded at both ends; the 2.1 V rms potential difference will drive current through that shield, causing noise, interference, and potential equipment damage. Multimode and Singlemode fiber are dielectric (non-conductive) and provide full electrical isolation between locations, making them safe choices. UTP has no shield to act as a ground conductor, so while not ideal, it does not create the same direct ground loop path that STP does. STP is the answer that should NOT be used.

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