VDV Cabling Infrastructure 4 — Questions and Answers
Question 1: What is the maximum length of a work area cable (equipment cord) between a wall outlet and an end device in TIA-568?
- 3 meters
- 5 meters
- 10 meters (Correct answer)
- 15 meters
Correct answer: 10 meters
TIA-568 allows up to 10 meters total for combined equipment cords at both ends of a horizontal channel, though individual work area cords are typically kept to 5 meters or less.
Question 2: When testing installed fiber with an OTDR, a 'ghost' reflection appears beyond the far end of the fiber. What is the most likely cause?
- A dirty connector at the far end
- A high-reflectance event re-reflecting back past the launch end (Correct answer)
- Fiber wrapped too tightly around a spool
- Incorrect wavelength selected on the OTDR
Correct answer: A high-reflectance event re-reflecting back past the launch end
Ghost reflections occur when a very strong Fresnel reflection (e.g., an open, polished end) bounces back to another high-reflectance point and re-reflects, appearing as a false event beyond the actual fiber end.
Question 3: Which backbone cabling topology is recommended by TIA-568 for campus environments?
- Ring
- Mesh
- Hierarchical star (Correct answer)
- Bus
Correct answer: Hierarchical star
TIA-568 recommends a hierarchical star topology for backbone cabling, with the campus distributor connecting to building distributors, which connect to floor distributors.
Question 4: A technician measures a near-end crosstalk (NEXT) loss of 28 dB on a Cat5e link. What does this result indicate?
- The link passes the Cat5e NEXT requirement
- The link fails because Cat5e requires a minimum of 35 dB NEXT at 100 MHz (Correct answer)
- The measurement is acceptable only for voice applications
- The result is within tolerance if the cable is under 50 meters
Correct answer: The link fails because Cat5e requires a minimum of 35 dB NEXT at 100 MHz
Cat5e requires a minimum NEXT loss of 35.3 dB at 100 MHz per TIA-568-C.2; a reading of 28 dB indicates insufficient isolation between pairs, meaning the link fails certification.
Question 5: What grounding method is used to protect coaxial cable shields in a video distribution system from lightning and power induction?
- Floating the shield at both ends
- Single-point grounding at the signal source only
- Bonding the shield to the building ground at each cable entry point (Correct answer)
- Using fiber optic cable instead of coax
Correct answer: Bonding the shield to the building ground at each cable entry point
NEC Article 820 requires that coaxial cable shields be bonded to the building's ground electrode system at the point where cables enter the structure to divert surge currents safely.
Question 6: In a structured cabling system, what is the recommended maximum distance for backbone copper cabling between a Building Distributor and a Floor Distributor?
- 90 meters (Correct answer)
- 100 meters
- 300 meters
- 500 meters
Correct answer: 90 meters
TIA-568 limits copper backbone cabling between building and floor distributors to 90 meters to maintain signal quality for voice and data applications.
Question 7: Which tool is used to terminate 110-style punch-down blocks without cutting wire tails manually?
- Krone tool
- Impact punch-down tool with 110 blade (Correct answer)
- Wire stripper
- Cable crimper
Correct answer: Impact punch-down tool with 110 blade
An impact punch-down tool fitted with a 110-style blade seats and cuts the conductor in one motion, providing consistent termination depth and cutting the excess wire tail.
VDV Cabling Infrastructure 4
What is the maximum length of a work area cable (equipment cord) between a wall outlet and an end device in TIA-568?