DCI Cable Installation Techniques 3 — Questions and Answers
Question 1: What is the primary purpose of leaving a service loop when terminating cable in a telecommunications room?
- To act as extra shielding
- To allow re-termination if a connection fails (Correct answer)
- To reduce crosstalk between cables
- To satisfy NEC bonding requirements
Correct answer: To allow re-termination if a connection fails
A service loop (typically 3–10 feet) provides enough extra cable length to re-terminate the end if a punch-down is damaged or needs to be moved.
Question 2: When installing horizontal cable, what is the maximum distance allowed from the work area outlet to the telecommunications room under TIA-568?
- 50 meters (164 ft)
- 90 meters (295 ft) (Correct answer)
- 100 meters (328 ft)
- 150 meters (492 ft)
Correct answer: 90 meters (295 ft)
TIA-568 limits horizontal cable (permanent link) to 90 meters to leave 10 meters for equipment and patch cords in the total 100-meter channel.
Question 3: Which wiring standard pinout is most commonly required for new commercial structured cabling installations in the US?
- T568A
- T568B (Correct answer)
- USOC
- EIA-310
Correct answer: T568B
T568B is the most commonly used pinout for commercial installations in the US, though T568A is specified for government and some enterprise environments.
Question 4: A cable installer notices the cable jacket is slightly crushed after installation through a conduit. What is the best course of action?
- Test the cable and replace only if it fails
- Remove and replace the cable regardless of test results (Correct answer)
- Apply electrical tape over the crush point
- Increase transmit power to compensate
Correct answer: Remove and replace the cable regardless of test results
A crushed jacket can deform internal pairs and cause latent failures; the cable should be replaced to ensure long-term reliability even if it initially passes testing.
Question 5: Which type of conduit fill table should be referenced when determining how many cables can be pulled through a 1-inch EMT conduit?
- NEC Article 300 fill tables
- NEC Chapter 9 conduit fill tables (Correct answer)
- TIA-569 pathway fill guidelines
- ANSI/NEMA VE 2 tables
Correct answer: NEC Chapter 9 conduit fill tables
NEC Chapter 9 tables provide conduit fill calculations for conductors and cables, specifying maximum fill percentages for different conduit types and sizes.
Question 6: What installation practice minimizes alien crosstalk (AXT) when running multiple Cat 6A cables in close proximity?
- Tightly bundling cables together
- Maintaining random, loose cable spacing without bundling (Correct answer)
- Using solid-conductor cable only
- Installing all cables in the same orientation
Correct answer: Maintaining random, loose cable spacing without bundling
Loose, random spacing without tight bundling prevents the consistent parallel alignment that maximizes alien crosstalk coupling between adjacent cables.
Question 7: When installing a cable through a suspended ceiling, which pathway guideline must the installer follow regarding cable support?
- Cables may rest freely on ceiling tiles
- Cables must be supported every 4–5 feet and not laid on ceiling tiles (Correct answer)
- Cables must be enclosed in metallic conduit at all times
- Only plenum-rated cable can run above suspended ceilings
Correct answer: Cables must be supported every 4–5 feet and not laid on ceiling tiles
TIA-569 and NEC require cables above suspended ceilings to be supported at intervals not exceeding 4–5 feet and must not rest on the ceiling tiles.
DCI Cable Installation Techniques 3
What is the primary purpose of leaving a service loop when terminating cable in a telecommunications room?