C7 C7 Audio Visual & Communication Systems 5 — Questions and Answers
Question 1: A C7 low-voltage contractor must pull a communication cable through the same conduit as a 120V branch circuit. Which NEC section generally prohibits this practice?
- NEC Article 300.11
- NEC Article 725.136
- NEC Article 800.133 (Correct answer)
- NEC Article 820.110
Correct answer: NEC Article 800.133
NEC Article 800.133 prohibits communications cables from being installed in the same raceway or conduit as electrical light and power conductors.
Question 2: What is the primary purpose of a DSP (Digital Signal Processor) in a commercial AV system?
- To convert analog audio to digital format only
- To route, mix, equalize, and apply dynamics processing to audio signals (Correct answer)
- To amplify speaker-level signals to line level
- To convert HDMI signals to analog audio
Correct answer: To route, mix, equalize, and apply dynamics processing to audio signals
A DSP performs routing, mixing, EQ, compression, delay, and other real-time processing on audio signals within a single digital domain.
Question 3: In a structured cabling installation, the maximum total channel length for a permanent link plus patch cords in a Class D (Cat5e) channel is:
- 90 meters
- 100 meters (Correct answer)
- 110 meters
- 120 meters
Correct answer: 100 meters
TIA-568 specifies a maximum channel length of 100 meters (328 ft) for Class D/Cat5e, including up to 10 meters of patch cords.
Question 4: A retail store needs background music distributed to 20 ceiling speakers. To maintain consistent volume levels at different distances from the amplifier, the installer should use:
- A series speaker wiring scheme
- A 70-volt distributed audio system with tap transformers (Correct answer)
- Individual stereo amplifiers per speaker zone
- Direct 4-ohm parallel wiring to all speakers
Correct answer: A 70-volt distributed audio system with tap transformers
A 70-volt system with tap transformers allows each speaker to be set to a specific wattage tap, maintaining consistent volume regardless of distance or total speaker count.
Question 5: Under the California C7 license, which of the following work requires a separate C-10 Electrical Contractor license and CANNOT be performed by a C7 licensee alone?
- Installing Cat6 data cabling in conduit
- Connecting low-voltage control wiring to a projector
- Installing a 120V dedicated outlet for an AV rack (Correct answer)
- Terminating coaxial cable to an RF connector
Correct answer: Installing a 120V dedicated outlet for an AV rack
Line-voltage electrical work such as installing 120V outlets requires a C-10 Electrical Contractor license; C7 licensees are restricted to low-voltage systems.
Question 6: Which video signal format provides the highest bandwidth and is required for uncompressed 8K video transmission over short distances in professional AV installations?
- HDMI 1.4
- DisplayPort 1.2
- HDMI 2.1 or DisplayPort 2.0 (Correct answer)
- SDI (Serial Digital Interface)
Correct answer: HDMI 2.1 or DisplayPort 2.0
HDMI 2.1 supports up to 48 Gbps and DisplayPort 2.0 up to 80 Gbps, both capable of carrying uncompressed 8K video signals.
Question 7: A C7 contractor installing a fire alarm notification speaker system must coordinate with which licensed trade for the initiating devices and control panel connections?
- C-7 contractor can perform all fire alarm work independently
- C-10 Electrical Contractor
- C-47 General Manufactured Housing Contractor
- C-16 Fire Protection Contractor (Correct answer)
Correct answer: C-16 Fire Protection Contractor
Fire alarm systems in California require a C-16 Fire Protection Contractor license for the overall system; C7 contractors may install speaker wiring but must coordinate panel and device work with a C-16 licensee.
C7 C7 Audio Visual & Communication Systems 5
A C7 low-voltage contractor must pull a communication cable through the same conduit as a 120V branch circuit.
Which NEC section generally prohibits this practice?