NEC Wiring Methods & Materials 3 — Questions and Answers
Question 1: Type MC cable installed in a wet location must be which of the following?
- Listed and identified for use in wet locations (Correct answer)
- Enclosed in a weatherproof conduit
- Limited to circuits of 30A or less
- Installed with a minimum 6-inch burial depth
Correct answer: Listed and identified for use in wet locations
NEC 330.10(A)(11) requires Type MC cable used in wet locations to be listed and identified for use in wet locations.
Question 2: What is the minimum size equipment grounding conductor required for a circuit protected by a 100A overcurrent device?
- 10 AWG copper
- 8 AWG copper (Correct answer)
- 6 AWG copper
- 4 AWG copper
Correct answer: 8 AWG copper
NEC Table 250.122 requires a minimum 8 AWG copper equipment grounding conductor for circuits with 100A overcurrent protection.
Question 3: Nonmetallic-sheathed cable (NM) is NOT permitted to be installed in which of the following?
- One-family dwellings
- Garages in residential occupancies
- Buildings exceeding three floors above grade (Correct answer)
- Attic spaces
Correct answer: Buildings exceeding three floors above grade
NEC 334.10 restricts Type NM cable use and prohibits it in buildings exceeding three floors above grade.
Question 4: When RMC passes through a concrete floor slab, which of the following is required at the termination above the slab?
- A conduit seal
- A bushing or equivalent protection (Correct answer)
- A conduit body
- A pull box
Correct answer: A bushing or equivalent protection
NEC 344.46 requires a bushing or equivalent protection at the end of RMC where it emerges from a floor slab to protect conductors from abrasion.
Question 5: What is the maximum length of a flexible metal conduit (FMC) connection at a luminaire in a ceiling assembly?
- 2 feet
- 3 feet
- 4 feet
- 6 feet (Correct answer)
Correct answer: 6 feet
NEC 348.20(A) permits FMC in lengths not exceeding 6 feet for connection of luminaires within a ceiling assembly.
Question 6: Which conductor insulation type is rated for use in a dry location only?
- THWN-2
- XHHW-2
- TW (Correct answer)
- THW
Correct answer: TW
NEC Table 310.4 lists TW insulation as rated for 60°C in wet or dry locations, but older TW (not wet-rated) applies only to dry — THWN-2 and XHHW-2 are wet-rated; TW without wet listing is dry only.
Question 7: When Type NM cable is run across the top of floor joists in an accessible attic, what protection is required within 6 feet of the attic access opening?
- Steel plates on each joist
- Guard strips at least as high as the cable (Correct answer)
- Metal conduit sleeve
- No protection is required
Correct answer: Guard strips at least as high as the cable
NEC 334.23(A) requires guard strips at least as high as the cable when NM cable runs across the top of floor joists within 6 feet of the scuttle hole or attic entrance.
NEC Wiring Methods & Materials 3
Type MC cable installed in a wet location must be which of the following?