Free E2 Wiring Methods and Materials Questions and Answers 1 — Questions and Answers
Question 1: An inspector observes a 40-foot continuous run of 1-inch Electrical Metallic Tubing (EMT) installed exposed on a commercial warehouse wall. What are the maximum permitted spacing requirements for securing and supporting this raceway according to NEC Article 358?
- Within 5 feet of each box and every 10 feet thereafter.
- Within 3 feet of each box and every 12 feet thereafter.
- Within 3 feet of each box and every 10 feet thereafter. (Correct answer)
- Within 18 inches of each box and every 8 feet thereafter.
Correct answer: Within 3 feet of each box and every 10 feet thereafter.
NEC 358.30(A) requires that EMT be securely fastened in place at least every 10 feet. Additionally, NEC 358.30(B) mandates that EMT must be securely fastened within 3 feet of each outlet box, junction box, device box, cabinet, or conduit body.
Question 2: According to NEC Table 310.15(C)(1), what is the required adjustment factor for the allowable ampacity of conductors when there are 8 current-carrying conductors installed in a single conduit?
- 80%
- 70% (Correct answer)
- 50%
- 100%
Correct answer: 70%
NEC Table 310.15(C)(1) provides adjustment factors for raceways or cables containing more than three current-carrying conductors. For 7 to 9 current-carrying conductors, the allowable ampacity of each conductor must be reduced to 70% of the value listed in the ampacity tables.
Question 3: When Type MC cable is installed through a field-punched hole in a steel stud in a commercial building, which of the following protection methods is required by the NEC?
- A steel plate must be installed on the face of the stud.
- The hole must be located at least 1-1/4 inches from the edge of the stud.
- A listed bushing or grommet must be installed in the opening. (Correct answer)
- The cable must be wrapped with electrical tape where it passes through the stud.
Correct answer: A listed bushing or grommet must be installed in the opening.
NEC 300.4(B)(1) requires that where cables pass through holes in metal members, the cable must be protected by a listed bushing or listed grommet that is securely fastened in the opening to protect the cable from the sharp metal edges.
Question 4: In a commercial building, which of the following wiring methods is generally prohibited by NEC Article 358 for use where it would be subject to severe physical damage?
- Rigid Metal Conduit (RMC)
- Intermediate Metal Conduit (IMC)
- Reinforced Thermosetting Resin Conduit (RTRC-XW)
- Electrical Metallic Tubing (EMT) (Correct answer)
Correct answer: Electrical Metallic Tubing (EMT)
NEC 358.12(1) explicitly states that Electrical Metallic Tubing (EMT) shall not be used where, during installation or afterward, it will be subject to severe physical damage. RMC, IMC, and other heavier-walled conduits are designed for such environments.
Question 5: An inspector is performing a box fill calculation for a metal device box. According to NEC 314.16(B)(4), what volume allowance must be made for a single duplex receptacle mounted on a single yoke?
- A single volume allowance based on the largest conductor connected to the device.
- No volume allowance is required for the device itself.
- A double volume allowance based on the largest conductor connected to the device. (Correct answer)
- A triple volume allowance based on the average size of conductors in the box.
Correct answer: A double volume allowance based on the largest conductor connected to the device.
NEC 314.16(B)(4) requires a double volume allowance for each yoke or strap containing one or more devices. This allowance is calculated based on the cubic inch volume for the largest conductor connected to the device, as specified in Table 314.16(B).
Question 6: Which of the following wiring methods is permitted by the NEC to be installed in direct contact with the earth (direct burial) when made of galvanized steel?
- Flexible Metal Conduit (FMC)
- Rigid Metal Conduit (RMC) (Correct answer)
- Article 362 Tubing (ENT)
- Armored Cable (Type AC)
Correct answer: Rigid Metal Conduit (RMC)
According to NEC 344.10(B), Rigid Metal Conduit (RMC) is permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition. Other methods like FMC, ENT, and Type AC are generally not permitted for direct burial.
