VDV Copper Cabling 4 — Questions and Answers
Question 1: When installing copper cabling near fluorescent lighting fixtures, what is the minimum separation distance recommended by TIA-569?
- 5 inches (12.7 cm) (Correct answer)
- 12 inches (30.5 cm)
- 24 inches (61 cm)
- 36 inches (91 cm)
Correct answer: 5 inches (12.7 cm)
TIA-569 recommends a minimum 5-inch separation between telecommunications cables and fluorescent fixtures to reduce EMI-induced noise.
Question 2: What is the purpose of the spline or cross-filler found inside some Cat6 cables?
- Maintain pair separation to reduce crosstalk between the four pairs (Correct answer)
- Increase the tensile strength of the cable for long pulls
- Serve as a central conductor for power delivery
- Provide a bonding point for the overall shield
Correct answer: Maintain pair separation to reduce crosstalk between the four pairs
The internal plastic spline physically separates the four pairs, maintaining consistent geometry that reduces near-end crosstalk in Cat6 cable.
Question 3: A field tester reports a 'split pair' fault. What wiring error causes this condition?
- One conductor from two different pairs is wired together instead of using a matched pair (Correct answer)
- Two conductors on the same pair are reversed in polarity
- An additional wire is shorted to an existing pair conductor
- One pin is left open/unconnected at the far end
Correct answer: One conductor from two different pairs is wired together instead of using a matched pair
A split pair occurs when wires from two different pairs are used together as a pair, destroying the balanced transmission and drastically increasing crosstalk.
Question 4: Which copper cabling characteristic is expressed in decibels per 100 meters (dB/100m) and represents signal power lost along the cable?
- Insertion loss (attenuation) (Correct answer)
- Return loss
- NEXT
- Impedance
Correct answer: Insertion loss (attenuation)
Insertion loss, also called attenuation, measures how much signal power is lost as it travels through the cable and is expressed as dB per unit length.
Question 5: In a T568A vs T568B comparison, which pairs are swapped between the two standards?
- Pairs 2 and 3 (the green and orange pairs) (Correct answer)
- Pairs 1 and 4 (the blue and brown pairs)
- Pairs 2 and 4 (the orange and brown pairs)
- Pairs 1 and 3 (the blue and green pairs)
Correct answer: Pairs 2 and 3 (the green and orange pairs)
T568A and T568B differ only in the positions of the orange and green pairs (pairs 2 and 3); all other pairs remain in the same pin positions.
Question 6: What is the characteristic impedance of standard Cat5e/Cat6 UTP cable?
- 100 ohms (Correct answer)
- 75 ohms
- 50 ohms
- 120 ohms
Correct answer: 100 ohms
All TIA-568 categories of UTP horizontal cabling have a nominal characteristic impedance of 100 ohms ± 15 ohms.
Question 7: A VDV technician is testing a newly installed Cat6 link and finds the 'PS-NEXT' value is failing. What does PS-NEXT measure?
- Power Sum NEXT — the combined crosstalk from all disturbing pairs onto one victim pair simultaneously (Correct answer)
- Peak Signal NEXT at the far-end connector
- Pair-Specific NEXT at the near end connector only
- Passive Shield NEXT for shielded cable assemblies
Correct answer: Power Sum NEXT — the combined crosstalk from all disturbing pairs onto one victim pair simultaneously
PS-NEXT (Power Sum NEXT) calculates the total crosstalk noise on a victim pair from all three other disturbing pairs combined, reflecting real-world multi-pair transmission.
VDV Copper Cabling 4
When installing copper cabling near fluorescent lighting fixtures, what is the minimum separation distance recommended by TIA-569?