DCI Cable Installation Techniques 5 — Questions and Answers
Question 1: What is the correct procedure when a cable tray changes direction horizontally by 90 degrees in a ceiling installation?
- Cut the tray and splice with a coupling plate
- Use a manufacturer-supplied horizontal elbow fitting (Correct answer)
- Overlap two tray sections and bolt them together
- Bend the tray sides with a sheet metal brake
Correct answer: Use a manufacturer-supplied horizontal elbow fitting
Manufacturer-supplied horizontal elbow fittings are designed to make direction changes while maintaining cable tray continuity, structural integrity, and proper bend radius.
Question 2: What type of cable labeling is required by TIA-606 at each end of every installed cable?
- A handwritten label on the cable jacket
- A machine-printed, permanent label identifying the cable's unique identifier (Correct answer)
- A color-coded cable tie only
- A label on the patch panel only, not the cable itself
Correct answer: A machine-printed, permanent label identifying the cable's unique identifier
TIA-606 requires machine-printed, durable labels with a unique identifier at both ends of every cable to ensure accurate documentation and traceability.
Question 3: Which grounding practice must be followed when installing shielded twisted pair (STP) cable to prevent ground loops?
- Ground the shield at both ends always
- Ground the shield at one end only (typically the telecommunications room) (Correct answer)
- Leave the shield floating with no ground connection
- Ground the shield at every cable support point
Correct answer: Ground the shield at one end only (typically the telecommunications room)
Shielded cable should typically be grounded at one end (the telecommunications room/equipment room) to prevent ground loops that can introduce noise onto the shield.
Question 4: What is the minimum clearance that must be maintained between low-voltage data cables and fluorescent lighting fixtures per TIA-569?
- 50 mm (2 in)
- 75 mm (3 in)
- 125 mm (5 in) (Correct answer)
- 300 mm (12 in)
Correct answer: 125 mm (5 in)
TIA-569 requires a minimum 125 mm (5 inch) separation between unshielded data cables and fluorescent lighting fixtures to reduce electromagnetic interference.
Question 5: When installing outlet boxes for data cabling in a commercial environment, what is the standard mounting height from the finished floor?
- 300 mm (12 in)
- 450 mm (18 in) (Correct answer)
- 450 mm (18 in) with tolerance of ±12 mm
- 610 mm (24 in)
Correct answer: 450 mm (18 in)
TIA-569 recommends outlet boxes for horizontal cabling be mounted at 450 mm (18 inches) above the finished floor as the standard height for work area outlets.
Question 6: A technician needs to install cable above a drop ceiling in a building with an HVAC air-return plenum. Which cable jacket rating is the minimum requirement?
- CMG (General Purpose)
- CMR (Riser rated)
- CMP (Plenum rated) (Correct answer)
- CM (General Purpose unlisted)
Correct answer: CMP (Plenum rated)
Any space used for HVAC air return requires CMP (plenum-rated) cable because the air movement can rapidly spread combustion products from non-plenum-rated cable jackets.
Question 7: Which installation error most commonly causes a 'split pair' fault detected during cable testing?
- Using the wrong pull tension on a conduit pull
- Connecting wires from two different pairs to the same jack position (Correct answer)
- Exceeding the 90-meter horizontal run distance
- Over-untwisting pairs at the termination point
Correct answer: Connecting wires from two different pairs to the same jack position
A split pair occurs when one wire from each of two different pairs is incorrectly placed together at a termination, ruining the balanced twisted pair configuration needed for noise rejection.
DCI Cable Installation Techniques 5
What is the correct procedure when a cable tray changes direction horizontally by 90 degrees in a ceiling installation?