DCI Cable Installation Techniques 4 — Questions and Answers
Question 1: What is the correct method for unshielded twisted pair (UTP) cable when transitioning from a vertical cable tray to horizontal routing?
- Use a sharp 90-degree bend secured with a cable tie
- Use a sweeping bend that maintains the minimum bend radius (Correct answer)
- Splice the cable at the transition point
- Install a balun at the transition
Correct answer: Use a sweeping bend that maintains the minimum bend radius
A sweeping bend that maintains the minimum bend radius (8x cable OD for Cat 6A) prevents deformation of the internal twist pairs at the transition point.
Question 2: Which of the following is true about installing plenum-rated (CMP) cable in a plenum air-handling space?
- CMP cable can be used in any space as a substitute for CMR cable
- CMP cable is required in plenum spaces due to its low-smoke, low-flame characteristics (Correct answer)
- CMP cable is only required in conduit within plenum spaces
- CMP cable has better electrical performance than CMR cable
Correct answer: CMP cable is required in plenum spaces due to its low-smoke, low-flame characteristics
CMP (Communications Multipurpose Plenum) cable is required in air-handling plenums because its jacket produces less smoke and flame spread, reducing fire hazards in HVAC air pathways.
Question 3: What is the recommended maximum untwist length when terminating a Cat 6 cable pair at a keystone jack?
- 13 mm (0.5 in) (Correct answer)
- 25 mm (1 in)
- 50 mm (2 in)
- 75 mm (3 in)
Correct answer: 13 mm (0.5 in)
TIA-568 recommends untwisting no more than 13 mm (0.5 inch) of each pair when terminating at an outlet or patch panel to preserve NEXT performance.
Question 4: When using a fish tape to pull cable through an existing wall cavity, which safety precaution is most critical?
- Wear rubber-soled shoes
- Verify there are no electrical conductors in the cavity before fishing (Correct answer)
- Use only steel fish tape
- Pull at maximum speed to avoid fatigue
Correct answer: Verify there are no electrical conductors in the cavity before fishing
Verifying the wall cavity is clear of electrical conductors before fishing prevents accidental contact with live wiring, which poses a serious electrocution risk.
Question 5: What is the purpose of a pulling lubricant (cable lube) during conduit pulls?
- To increase the cable's electrical conductivity
- To reduce friction and lower the pulling tension needed (Correct answer)
- To waterproof the cable jacket
- To improve cable flexibility after installation
Correct answer: To reduce friction and lower the pulling tension needed
Cable lubricant reduces friction between the cable jacket and conduit walls, keeping pulling tension below the cable's maximum rated limit.
Question 6: Which measurement does a cable installer record to verify the cable length does not exceed the 90-meter horizontal limit?
- Propagation delay
- Cable length as measured by a certifying tester's TDR function (Correct answer)
- Attenuation at 100 MHz
- Return loss at 250 MHz
Correct answer: Cable length as measured by a certifying tester's TDR function
A certifying tester uses Time Domain Reflectometry (TDR) to measure the actual electrical length of the installed cable in meters.
Question 7: When pulling multiple cables simultaneously through a conduit, what technique prevents the cables from binding and twisting around each other?
- Attaching each cable to a separate pull string
- Using a breakaway swivel or pulling grip with a rotating attachment (Correct answer)
- Taping all cable ends together into one bundle
- Pulling all cables from opposite ends simultaneously
Correct answer: Using a breakaway swivel or pulling grip with a rotating attachment
A breakaway swivel or rotating pulling grip allows the pull line to rotate freely, preventing torque from twisting and tangling the cables during the pull.
DCI Cable Installation Techniques 4
What is the correct method for unshielded twisted pair (UTP) cable when transitioning from a vertical cable tray to horizontal routing?