CPCT Cable Testing & Troubleshooting 2 — Questions and Answers
Question 1: A field tester reports a 'split pair' fault on a Cat 6 cable. Which symptom is most characteristic of this wiring error?
- High insertion loss on all pairs
- Correct continuity but excessive near-end crosstalk (NEXT) (Correct answer)
- Open circuit on one conductor
- Excessive return loss on pair 1-2
Correct answer: Correct continuity but excessive near-end crosstalk (NEXT)
A split pair passes continuity tests but causes severe NEXT because the twisted pairs are not maintained, disrupting the balanced transmission.
Question 2: During TDR testing of a coaxial cable, a reflected pulse appears with the same polarity as the transmitted pulse. What does this indicate?
- A short circuit fault
- An open circuit fault (Correct answer)
- Correct impedance termination
- A capacitive splice
Correct answer: An open circuit fault
An open circuit reflects the pulse with the same polarity because the impedance at the fault is higher than the cable's characteristic impedance.
Question 3: What does the 'PS NEXT' measurement evaluate in structured cabling testing?
- Near-end crosstalk from a single aggressor pair
- The combined crosstalk effect of all other pairs acting simultaneously on one pair (Correct answer)
- Far-end crosstalk summed across all pairs
- Power sum of insertion loss values
Correct answer: The combined crosstalk effect of all other pairs acting simultaneously on one pair
Power Sum NEXT (PS NEXT) measures the cumulative near-end crosstalk induced on one pair by the simultaneous transmission on all other pairs in the cable.
Question 4: A technician measures a cable length of 312 feet using a TDR but the actual measured physical length is only 295 feet. What is the most likely cause?
- The cable has excessive attenuation
- The NVP value entered is too high (Correct answer)
- The NVP value entered is too low
- There is a short circuit near the far end
Correct answer: The NVP value entered is too high
If the NVP entered is too high, the tester calculates a longer electrical length than the actual physical length, resulting in an over-reported distance.
Question 5: Which ANSI/TIA standard defines the performance parameters and test limits for Category 6A permanent links?
- TIA-568-B.1
- TIA-568-C.2
- TIA-568-D.2 / TIA-568.2-D (Correct answer)
- TIA-606-C
Correct answer: TIA-568-D.2 / TIA-568.2-D
TIA-568.2-D (formerly TIA-568-C.2) specifies balanced twisted-pair cabling components and performance limits including Category 6A.
Question 6: A patch panel port consistently fails the return loss test but passes all other parameters. Which condition is the most probable cause?
- Excessive cable length beyond 90 meters
- An impedance mismatch at the punch-down termination (Correct answer)
- Reversed polarity on one pair
- Insufficient jacket strip length
Correct answer: An impedance mismatch at the punch-down termination
Poor termination technique causing an impedance discontinuity at the punch-down point is a primary cause of return loss failures.
Question 7: What is the maximum allowed permanent link length for Category 6 cabling per TIA-568 when supporting 10GBASE-T?
- 55 meters
- 90 meters (Correct answer)
- 100 meters
- 37 meters
Correct answer: 90 meters
The standard permanent link maximum is 90 meters regardless of application; 10GBASE-T may restrict channel length to 55 m in some environments, but the permanent link limit remains 90 m.
CPCT Cable Testing & Troubleshooting 2
A field tester reports a 'split pair' fault on a Cat 6 cable.
Which symptom is most characteristic of this wiring error?