CPCT Cable Testing & Troubleshooting 5 — Questions and Answers
Question 1: A technician is troubleshooting a Cat 6A channel where 10GBASE-T is experiencing frequent errors. All individual pair parameters pass certification. Which additional test should be performed?
- DC loop resistance
- Alien crosstalk (ANEXT/AACR-F) on the channel (Correct answer)
- Cable jacket integrity using a megohmmeter
- Voltage on the pairs using a multimeter
Correct answer: Alien crosstalk (ANEXT/AACR-F) on the channel
10GBASE-T is highly susceptible to alien crosstalk; ANEXT and AACR-F testing evaluates interference from adjacent cables that internal pair tests do not capture.
Question 2: What does the term 'headroom' mean in the context of cable certification testing?
- The physical clearance above cable trays in the ceiling
- The margin by which a measured value exceeds (or falls short of) the pass/fail limit (Correct answer)
- The extra cable length left for future moves or changes
- The additional gain provided by the test equipment
Correct answer: The margin by which a measured value exceeds (or falls short of) the pass/fail limit
Headroom is the difference between the measured performance value and the test limit, indicating how much margin exists before the parameter would fail.
Question 3: During fiber certification, an OTDR event table shows a reflective event followed immediately by a non-reflective event at the same location. What does this combination most likely represent?
- Two mechanical splices stacked together
- A dirty or damaged connector followed by a fusion splice
- A connector mated to a bulkhead adapter (Correct answer)
- A fiber bend exceeding the minimum bend radius
Correct answer: A connector mated to a bulkhead adapter
A connector in a bulkhead adapter produces a reflective event (Fresnel reflection at the glass-air interface) and the loss appears as a non-reflective loss at the same location.
Question 4: Which test instrument would be BEST suited to identify the specific location of a coax cable fault in a CATV distribution system within a building?
- Optical power meter
- Time domain reflectometer (TDR) (Correct answer)
- Optical time domain reflectometer (OTDR)
- Spectrum analyzer
Correct answer: Time domain reflectometer (TDR)
A TDR sends electrical pulses into the coaxial cable and measures reflections to locate impedance discontinuities such as opens, shorts, or damage.
Question 5: A Cat 5e cable link passes all parameters except for pair delay skew, which measures 60 ns. What is the TIA-568 maximum allowed pair delay skew for this category?
- 25 ns
- 50 ns (Correct answer)
- 45 ns
- 100 ns
Correct answer: 50 ns
TIA-568 specifies a maximum pair-to-pair delay skew of 50 ns for Category 5e and Category 6 cabling.
Question 6: When troubleshooting an intermittent connectivity problem on a copper link, a technician suspects a failing connector. Which test method is most effective for revealing an intermittent fault?
- Static wiremap test with the cable at rest
- Dynamic stress test — flexing connectors and cables during continuous link monitoring (Correct answer)
- OTDR scan at both wavelengths
- DC resistance measurement at room temperature
Correct answer: Dynamic stress test — flexing connectors and cables during continuous link monitoring
Flexing the cable and connector during testing stresses the intermittent connection, causing it to open or short and be captured by the tester.
Question 7: A link tester displays 'FAIL — Propagation Delay' on a Category 6 run. Which condition would most commonly cause this failure?
- Excessive near-end crosstalk between pairs
- The cable run exceeds the maximum length, increasing travel time beyond the limit (Correct answer)
- A reversed pair at one end of the link
- High DC resistance on one conductor
Correct answer: The cable run exceeds the maximum length, increasing travel time beyond the limit
Propagation delay increases proportionally with cable length; a run exceeding 100 meters will typically produce a propagation delay failure.
CPCT Cable Testing & Troubleshooting 5
A technician is troubleshooting a Cat 6A channel where 10GBASE-T is experiencing frequent errors.
All individual pair parameters pass certification.
Which additional test should be performed?