Free NEC Wiring Methods and Materials Questions and Answers — Questions and Answers
Question 1: An electrician is installing Type NM cable in the attic of a single-family dwelling. The cable is run across the top of 4-inch ceiling joists. According to NEC 2023, which of the following installations is compliant?
- The cable is run through bored holes in the joists that are at least 1 1/4 inches from the nearest edge.
- The cable is secured directly to the top of the ceiling joists without any additional protection.
- The cable is protected by guard strips that are at least as high as the cable. (Correct answer)
- The cable is installed within 6 feet of the scuttle hole without guard strips.
Correct answer: The cable is protected by guard strips that are at least as high as the cable.
According to NEC Section 334.23(A), where Type NM cable is run across the top of floor joists, or across the face of rafters or studs within 7 feet of the floor or floor joists, the cable must be protected by guard strips at least as high as the cable. Running the cable through bored holes is a different method, and simply securing it to the top or installing it near the scuttle hole without protection is a violation if the attic is accessible.
Question 2: When identifying a 4 AWG or larger grounded conductor at its terminations, which of the following methods is NOT permitted by NEC 2023?
- A continuous white outer finish along its entire length.
- Three continuous white stripes along the conductor's entire length on other-than-green insulation.
- Marking the insulation with white tape that encircles the conductor.
- Coloring the exposed insulation green at the termination. (Correct answer)
Correct answer: Coloring the exposed insulation green at the termination.
NEC Section 200.6(B) permits grounded conductors 4 AWG and larger to be identified by a continuous white or gray outer finish, three continuous white or gray stripes, or by marking the insulation at the terminations with a white or gray marking that encircles the conductor. Green is exclusively used for identifying equipment grounding conductors, not grounded (neutral) conductors, as stated in NEC 250.119.
Question 3: An installer is running multiple wiring methods in a space used for environmental air-handling, otherwise known as a plenum. Which of the following wiring methods is generally permitted in this space without being enclosed in a raceway?
- Type NM (Nonmetallic-Sheathed) Cable
- Type AC (Armored) Cable
- Type MC (Metal-Clad) Cable with an overall nonmetallic jacket
- Type CMP (Communications Plenum) Cable (Correct answer)
Correct answer: Type CMP (Communications Plenum) Cable
According to NEC 300.22(C), the wiring methods permitted in 'Other Space Used for Environmental Air (Plenum)' include totally enclosed, nonventilated, insulated busway, electrical metallic tubing, rigid metal conduit, intermediate metal conduit, flexible metallic tubing, and Type MC cable without an overall nonmetallic covering. For communications circuits, specifically listed plenum-rated cables like Type CMP are permitted as per Article 800. Type NM cable and MC cable with a nonmetallic jacket are generally not permitted due to their smoke and fire characteristics.
Question 4: What is the maximum allowable percentage of cross-sectional area that can be filled in a conduit when installing three or more conductors?
- 31%
- 53%
- 40% (Correct answer)
- 60%
Correct answer: 40%
According to NEC Chapter 9, Table 1, the permissible conduit fill for three or more conductors is 40% of the total interior cross-sectional area of the conduit. The 53% fill is for a single conductor, and 31% is for two conductors. 60% is only allowed for nipples not exceeding 24 inches in length.
Question 5: An electrician needs to support a run of 1-inch Electrical Metallic Tubing (EMT) in a commercial building. According to NEC Article 358, the EMT must be securely fastened within what distance of each outlet box, junction box, or cabinet?
- 12 inches
- 5 feet
- 10 feet
- 3 feet (Correct answer)
Correct answer: 3 feet
NEC Section 358.30(A) requires that EMT be securely fastened in place at least every 10 feet. In addition, it must be securely fastened within 3 feet of each outlet box, junction box, device box, cabinet, conduit body, or other tubing termination.
Question 6: Under which of the following conditions is Type MC (Metal-Clad) cable, with four or fewer conductors sized no larger than 10 AWG, required to be secured at intervals NOT exceeding 6 feet?
- When fished through concealed spaces in finished buildings
- When installed horizontally through wooden framing members
- In all standard exposed installations (Correct answer)
- Only when installed in a vertical orientation
Correct answer: In all standard exposed installations
NEC Section 330.30(B) states that unless otherwise provided, Type MC cable shall be secured at intervals not exceeding 6 ft. An exception in 330.30(C) notes that cables installed horizontally through wood or metal framing members are considered supported and secured, but this does not negate the general securing requirement for exposed work. Fishing cable in concealed spaces (330.30(D)) exempts it from the support requirement. Therefore, for standard exposed work, the 6-foot interval applies.
Free NEC Wiring Methods and Materials Questions and Answers
An electrician is installing Type NM cable in the attic of a single-family dwelling.
The cable is run across the top of 4-inch ceiling joists.
According to NEC 2023, which of the following installations is compliant?