VDV Cabling Infrastructure 5 — Questions and Answers
Question 1: What is the minimum separation distance required between unshielded communications cables and open fluorescent lighting fixtures per TIA-569?
- 50 mm (2 inches)
- 100 mm (4 inches)
- 150 mm (6 inches) (Correct answer)
- 300 mm (12 inches)
Correct answer: 150 mm (6 inches)
TIA-569 requires at least 150 mm (6 inches) of separation between unshielded communications cables and open (unshielded) fluorescent light fixtures to reduce electromagnetic interference.
Question 2: A VDV technician is asked to install cabling in a riser between floors. Which cable jacket rating is required?
- CM
- CMR (Correct answer)
- CMP
- CMX
Correct answer: CMR
CMR (Communications Riser) rated cable is required for vertical runs between floors because it is designed to resist flame spread in vertical shafts without the full plenum rating.
Question 3: Which fiber optic test instrument measures the end-to-end insertion loss of a fiber link using a known light source?
- OTDR
- Optical Power Meter with Light Source (OLTS) (Correct answer)
- Visual Fault Locator (VFL)
- Chromatic dispersion analyzer
Correct answer: Optical Power Meter with Light Source (OLTS)
An OLTS (Optical Loss Test Set) consisting of a calibrated light source and power meter measures total insertion loss through the entire fiber link, which is the required acceptance test per TIA-568.
Question 4: When pulling fiber optic cable through conduit, which method best protects the cable from damage?
- Attaching the pull rope directly to the buffer tube
- Using a Kellems mesh grip sized to the cable OD (Correct answer)
- Taping the fiber end to a steel fish tape
- Using a come-along winch at maximum tension
Correct answer: Using a Kellems mesh grip sized to the cable OD
A Kellems (woven wire mesh) pulling grip distributes tension evenly along the cable jacket rather than concentrating stress at a single point, preventing damage to the fiber strands inside.
Question 5: What is the purpose of a telecommunications bonding backbone (TBB) conductor being sized larger as it gets longer per TIA-607?
- To carry higher current for PoE devices
- To compensate for increased resistance over longer lengths and maintain bonding effectiveness (Correct answer)
- To match impedance with the cable it runs alongside
- To meet NEC ampacity requirements for power conductors
Correct answer: To compensate for increased resistance over longer lengths and maintain bonding effectiveness
TIA-607 requires the TBB conductor to increase in cross-sectional area as its length increases so that DC resistance remains low, ensuring effective equalization of ground potential throughout the building.
Question 6: A coaxial cable measures 75 ohms impedance. For which application is this impedance standard most commonly specified?
- RF and video signal distribution (Correct answer)
- Token Ring networks
- RS-232 serial communications
- Ethernet 10BASE2 networks
Correct answer: RF and video signal distribution
75-ohm coaxial cable (e.g., RG-6, RG-59) is the industry standard for CATV, satellite, and video distribution systems, while 50-ohm coax is used for data and RF transmission equipment.
Question 7: Which of the following is a key advantage of using pre-terminated fiber trunk cables in a data center installation?
- They eliminate the need for fiber testing after installation
- They reduce installation time and minimize splice loss by factory-polishing connectors (Correct answer)
- They allow field technicians to adjust connector type after installation
- They cost less per foot than field-terminated bulk fiber
Correct answer: They reduce installation time and minimize splice loss by factory-polishing connectors
Factory pre-terminated trunks arrive with precisely polished connectors and factory-tested performance, significantly reducing on-site labor and providing consistent, low-loss terminations compared to field work.
VDV Cabling Infrastructure 5
What is the minimum separation distance required between unshielded communications cables and open fluorescent lighting fixtures per TIA-569?