DCI Copper Installation 3 — Questions and Answers
Question 1: What is the primary reason copper cables should not be bundled tightly with cable ties over long runs?
- It increases impedance mismatches
- It can deform the cable and increase alien crosstalk (Correct answer)
- It violates NEC color-coding requirements
- It makes future testing impossible
Correct answer: It can deform the cable and increase alien crosstalk
Overtightening cable ties deforms the cable geometry, disrupts pair twists, and increases alien crosstalk (AXT) between adjacent cables.
Question 2: Which category of UTP cable first introduced alien crosstalk (AXT) testing as a required measurement?
- Category 5e
- Category 6
- Category 6A (Correct answer)
- Category 7
Correct answer: Category 6A
Category 6A introduced mandatory alien crosstalk testing because at 10GBASE-T frequencies, interference between adjacent cables becomes significant.
Question 3: A cable tester reports 'FAIL – Wire Map: Pair Reversal on pair 2.' What does this indicate?
- The two wires of pair 2 are swapped at one end (Correct answer)
- Pair 2 is open at mid-span
- Pair 2 is crossed with pair 3
- The shield on pair 2 is broken
Correct answer: The two wires of pair 2 are swapped at one end
A pair reversal means the tip and ring (the two conductors) of a pair are swapped at one termination end.
Question 4: What does the acronym 'PSANEXT' stand for in copper cabling testing?
- Power Sum Attenuation to Near-End Crosstalk
- Phase-Shift Alien Near-End Crosstalk
- Power Sum Alien Near-End Crosstalk (Correct answer)
- Partial Sum Attenuation Noise-End Cross Talk
Correct answer: Power Sum Alien Near-End Crosstalk
PSANEXT (Power Sum Alien Near-End Crosstalk) measures the combined alien crosstalk interference from multiple surrounding cables at the near end.
Question 5: What is the standard maximum length for a horizontal cable run from the telecommunications room to the work area outlet?
- 50 meters
- 70 meters
- 90 meters (Correct answer)
- 100 meters
Correct answer: 90 meters
ANSI/TIA-568 specifies a maximum of 90 meters (295 feet) for permanent horizontal cabling, leaving 10 meters for patch cords and equipment cords.
Question 6: Which copper cable installation practice helps reduce EMI susceptibility in a cable run near fluorescent lighting?
- Use shielded (STP/FTP) cable (Correct answer)
- Increase cable pulling tension
- Use solid copper instead of stranded
- Reduce the number of twists per foot
Correct answer: Use shielded (STP/FTP) cable
Shielded twisted pair (STP/FTP) cable provides a metallic barrier that attenuates external electromagnetic interference from sources like fluorescent lights.
Question 7: What is the correct procedure when a copper cable must cross a power cable in a conduit pathway?
- Run them parallel at a minimum 6-inch separation
- Cross at a 90-degree angle to minimize inductive coupling (Correct answer)
- Wrap the copper cable in foil tape at the crossing
- Install a ferrite bead at the crossing point
Correct answer: Cross at a 90-degree angle to minimize inductive coupling
Crossing power and data cables at 90 degrees minimizes the inductive coupling area, reducing the potential for EMI.
DCI Copper Installation 3
What is the primary reason copper cables should not be bundled tightly with cable ties over long runs?