PC Wiring Methods and Protection 2 — Questions and Answers
Question 1: What is the minimum cover requirement for direct-buried conductors rated 0–600V in a residential driveway under a concrete slab?
- 6 inches (Correct answer)
- 12 inches
- 18 inches
- 24 inches
Correct answer: 6 inches
NEC Table 300.5 allows a 6-inch minimum cover for conductors under a concrete encasement at least 2 inches thick.
Question 2: Which wiring method is specifically listed for use in ducts, plenums, or other air-handling spaces without restriction?
- Type MC cable
- EMT with THHN conductors (Correct answer)
- Type AC cable
- Electrical nonmetallic tubing (ENT)
Correct answer: EMT with THHN conductors
EMT with THHN conductors is permitted in environmental air spaces; Type MC, AC, and ENT have restrictions under NEC 300.22.
Question 3: Per NEC 300.14, at least how much free conductor length must be left at each outlet, junction, or switch point?
- 4 inches
- 6 inches (Correct answer)
- 8 inches
- 12 inches
Correct answer: 6 inches
NEC 300.14 requires at least 6 inches of free conductor at every outlet, switch, or junction point for splicing or connecting.
Question 4: Flexible metal conduit (FMC) used as a grounding path must not exceed what maximum length?
- 3 feet
- 6 feet (Correct answer)
- 8 feet
- 10 feet
Correct answer: 6 feet
Per NEC 350.60, FMC is permitted as an equipment grounding conductor only when the total length in the ground return path does not exceed 6 feet.
Question 5: What is the maximum size of rigid metallic conduit (RMC) recognized by the NEC?
- 3 inches
- 4 inches
- 5 inches
- 6 inches (Correct answer)
Correct answer: 6 inches
NEC 344.20 lists RMC in trade sizes from ½ inch through 6 inches.
Question 6: When installing conductors in a raceway exposed to different temperatures, what NEC rule applies to prevent moisture condensation?
- Install vapor barriers at both ends
- Seal the raceway at the point of temperature transition (Correct answer)
- Use only dry-location rated conductors throughout
- Install drain fittings at the lowest point
Correct answer: Seal the raceway at the point of temperature transition
NEC 300.7(A) requires raceways to be sealed where they pass between areas of different temperatures to prevent condensation from traveling to warmer areas.
Question 7: Type NM cable is NOT permitted in which of the following applications?
- Single-family dwellings
- Multifamily dwellings not exceeding 3 floors above grade
- Exposed in a residential garage
- Exposed industrial occupancies (Correct answer)
Correct answer: Exposed industrial occupancies
NEC 334.10 prohibits Type NM cable in commercial or industrial occupancies where exposed wiring is required to be in conduit.
PC Wiring Methods and Protection 2
What is the minimum cover requirement for direct-buried conductors rated 0–600V in a residential driveway under a concrete slab?