C7 C7 Audio Visual & Communication Systems 4 — Questions and Answers
Question 1: When terminating a Cat6 cable for a VoIP phone system, which wiring standard is most commonly specified in commercial California installations?
- TIA-568-A
- TIA-568-B
- TIA-568-C
- Either A or B as long as both ends match (Correct answer)
Correct answer: Either A or B as long as both ends match
Both TIA-568-A and TIA-568-B are acceptable; the critical requirement is that both ends of the cable use the same standard to maintain continuity.
Question 2: A conference room AV system requires 4K video distribution over HDBaseT. What is the maximum recommended cable run length for HDBaseT at 4K/60Hz with 4:4:4 color?
- 50 meters
- 70 meters (Correct answer)
- 100 meters
- 150 meters
Correct answer: 70 meters
HDBaseT at 4K/60Hz with 4:4:4 chroma sampling is limited to approximately 70 meters over Cat6A cable.
Question 3: Under California's Title 24 energy code, an automatically controlled commercial audio system must include which feature?
- A manual override lockout
- An auto-off timer when the space is unoccupied (Correct answer)
- A minimum volume limiter
- A dedicated 20A circuit
Correct answer: An auto-off timer when the space is unoccupied
Title 24 requires commercial AV systems to have automatic shutoff controls that turn off equipment when the space is unoccupied.
Question 4: Which impedance is standard for a distributed 70-volt speaker system used in commercial paging applications?
- 4 ohms
- 8 ohms
- 70.7 volts nominal, transformer-matched (Correct answer)
- 600 ohms
Correct answer: 70.7 volts nominal, transformer-matched
70-volt systems use step-up/step-down transformers at each speaker to match impedance, allowing many speakers on a single amplifier output without complex parallel calculations.
Question 5: A C7 contractor is installing a video surveillance system that stores footage locally. Under California law, what is the minimum retention period typically required for recorded footage in a licensed cannabis retail facility?
- 7 days
- 30 days
- 45 days (Correct answer)
- 90 days
Correct answer: 45 days
California DCC regulations require cannabis licensees to retain surveillance video footage for a minimum of 45 calendar days.
Question 6: When installing ceiling speakers in a plenum space without conduit, the audio cable must be rated as:
- CL2
- CL3
- CMP (plenum-rated) (Correct answer)
- CMR (riser-rated)
Correct answer: CMP (plenum-rated)
Cables run in air-handling plenums must be CMP-rated (plenum) to meet NEC Article 800 fire and smoke propagation requirements.
Question 7: An AV technician is troubleshooting a ground loop hum in a balanced XLR audio system. The most effective first corrective step is to:
- Add a 100-ohm resistor across the signal leads
- Insert a 1:1 isolation transformer on the affected run (Correct answer)
- Replace all XLR cables with unbalanced RCA cables
- Increase the amplifier gain
Correct answer: Insert a 1:1 isolation transformer on the affected run
An audio isolation transformer breaks the DC ground path while passing the audio signal, eliminating ground loop–induced hum without degrading signal quality.
C7 C7 Audio Visual & Communication Systems 4
When terminating a Cat6 cable for a VoIP phone system, which wiring standard is most commonly specified in commercial California installations?