Licensed Electrical Contractor Wiring Methods and Materials 3 — Questions and Answers
Question 1: When using liquidtight flexible nonmetallic conduit (LFNC), what is the maximum length permitted for a single run used as a fixed raceway?
- 3 feet
- 6 feet (Correct answer)
- 12 feet
- No limit
Correct answer: 6 feet
NEC 356.60 limits LFNC used as a fixed raceway to 6 feet in length except where used for lighting fixtures or where flexibility is necessary.
Question 2: Which insulation type is rated for use in both wet and dry locations at 75°C?
- THHN
- TW
- THW (Correct answer)
- THWN-2
Correct answer: THW
Type THW is rated 75°C in both wet and dry locations, making it suitable for outdoor or damp environment wiring.
Question 3: Intermediate metal conduit (IMC) has a wall thickness that is:
- The same as rigid metal conduit (RMC)
- Thicker than RMC
- Thinner than RMC but thicker than EMT (Correct answer)
- The same as EMT
Correct answer: Thinner than RMC but thicker than EMT
IMC has a wall thickness between the heavy-wall RMC and the thin-wall EMT, offering a balance of strength and weight savings.
Question 4: What is the maximum ambient temperature rating for Type THHN conductors?
- 60°C
- 75°C
- 90°C (Correct answer)
- 105°C
Correct answer: 90°C
Type THHN conductors are rated for 90°C in dry locations, though ampacity is typically derated to 75°C at terminations per NEC 110.14(C).
Question 5: When Type NM cable passes through a metal framing member, which protection is required?
- No protection needed if the hole is centered
- A listed bushing or grommet
- A steel nail plate at least 1/16 inch thick (Correct answer)
- Conduit sleeve through the entire member
Correct answer: A steel nail plate at least 1/16 inch thick
NEC 300.4(B)(1) requires a steel nail plate at least 1/16-inch thick to protect NM cable passing through metal framing members less than 1-1/4 inches from the edge.
Question 6: Polyvinyl chloride (PVC) conduit Schedule 40 is NOT permitted to be used:
- In wet locations
- As an equipment grounding conductor path alone (Correct answer)
- Embedded in concrete slabs
- As an exposed outdoor raceway
Correct answer: As an equipment grounding conductor path alone
PVC conduit is non-metallic and cannot serve as an equipment grounding path; a separate EGC must be installed inside per NEC 352.60.
Question 7: What is the minimum size rigid metal conduit permitted for use as a raceway?
- 1/2 inch trade size (Correct answer)
- 3/8 inch trade size
- 1/4 inch trade size
- 3/4 inch trade size
Correct answer: 1/2 inch trade size
NEC 344.20 establishes 1/2-inch trade size as the minimum size for rigid metal conduit used as a wiring method.
Licensed Electrical Contractor Wiring Methods and Materials 3
When using liquidtight flexible nonmetallic conduit (LFNC), what is the maximum length permitted for a single run used as a fixed raceway?