C7 Low Voltage System Design & Installation 2 — Questions and Answers
Question 1: What is the maximum allowable voltage for a Class 2 circuit under the California Electrical Code?
- 30 volts AC or 60 volts DC (Correct answer)
- 50 volts AC or 100 volts DC
- 24 volts AC or 48 volts DC
- 120 volts AC or 240 volts DC
Correct answer: 30 volts AC or 60 volts DC
Class 2 circuits are limited to 30V AC or 60V DC to reduce shock and fire hazards per CEC Article 725.
Question 2: When installing Category 6 cable in a plenum space, which cable jacket type is required?
- CMP (Communications Plenum) (Correct answer)
- CMR (Communications Riser)
- CM (Communications General)
- CMX (Communications Limited Use)
Correct answer: CMP (Communications Plenum)
CMP-rated cable is required in plenum air-handling spaces due to its low-smoke, flame-retardant jacket properties.
Question 3: In a structured cabling installation, what is the maximum distance allowed for a horizontal cable run from the telecommunications outlet to the horizontal cross-connect?
- 90 meters (295 feet) (Correct answer)
- 100 meters (328 feet)
- 75 meters (246 feet)
- 110 meters (361 feet)
Correct answer: 90 meters (295 feet)
ANSI/TIA-568 limits horizontal cable runs to 90 meters, reserving 10 meters for patch cords and equipment cables.
Question 4: Which conduit fill percentage applies when pulling three conductors through a conduit in a low voltage installation?
- 40% (Correct answer)
- 53%
- 31%
- 60%
Correct answer: 40%
NEC/CEC Table 1, Chapter 9 limits conduit fill to 40% of internal cross-sectional area for three or more conductors.
Question 5: What grounding method is required for the cable sheath of coaxial cables used in CATV systems entering a building?
- Bond to the building's grounding electrode system at the point of entry (Correct answer)
- Bond only to the nearest metallic water pipe
- Leave ungrounded if the signal is low power
- Bond to the electrical panel neutral bar
Correct answer: Bond to the building's grounding electrode system at the point of entry
CEC Article 820 requires coaxial cable shields to be bonded to the grounding electrode system at the building entry point to protect against lightning surges.
Question 6: A C7 contractor is designing a fire alarm notification appliance circuit (NAC). What is the maximum allowable voltage drop on a supervised NAC circuit?
- The voltage at the last appliance must meet the appliance's minimum rated operating voltage (Correct answer)
- No more than 5% drop across the entire circuit
- No more than 10 volts regardless of supply voltage
- Voltage drop is not regulated for NAC circuits
Correct answer: The voltage at the last appliance must meet the appliance's minimum rated operating voltage
NFPA 72 requires that all notification appliances receive at least their minimum listed operating voltage; the contractor must calculate wire resistance to ensure compliance.
Question 7: Under California Title 19, which entity is responsible for approving the fire alarm system design before installation begins?
- The local Authority Having Jurisdiction (AHJ) (Correct answer)
- The California Department of Consumer Affairs
- The State Fire Marshal's office exclusively
- The installing contractor solely
Correct answer: The local Authority Having Jurisdiction (AHJ)
The Authority Having Jurisdiction (AHJ), typically the local fire department or building department, must approve fire alarm system designs before installation.
C7 Low Voltage System Design & Installation 2
What is the maximum allowable voltage for a Class 2 circuit under the California Electrical Code?