IEC Wiring Methods and Materials 2 — Questions and Answers
Question 1: What is the minimum bending radius for a 1-inch rigid metal conduit (RMC)?
- 4 inches
- 6 inches (Correct answer)
- 8 inches
- 10 inches
Correct answer: 6 inches
NEC Table 344.24 requires a minimum bending radius of 6 times the trade size for 1-inch RMC, which equals 6 inches.
Question 2: Which wiring method is specifically prohibited in commercial kitchens above a suspended ceiling where the space is used as a return air plenum?
- Type MC cable with a listed jacket
- Rigid metal conduit (RMC)
- Type AC cable (BX) (Correct answer)
- Electrical metallic tubing (EMT)
Correct answer: Type AC cable (BX)
Type AC cable (BX) is not listed for use in plenum spaces; only wiring methods with plenum-rated cables or raceways are permitted per NEC 300.22(C).
Question 3: When installing conductors in a conduit, what is the maximum fill percentage allowed for three or more conductors?
- 40%
- 53%
- 31% (Correct answer)
- 60%
Correct answer: 31%
NEC Chapter 9, Table 1 limits conduit fill to 40% for two conductors and 31% for three or more conductors.
Question 4: Type UF cable is specifically designed and listed for which application?
- Use in conduit systems indoors only
- Direct burial in the earth without conduit (Correct answer)
- Use in hazardous locations
- Installation in cable trays only
Correct answer: Direct burial in the earth without conduit
Type UF (Underground Feeder) cable is listed for direct burial applications per NEC Article 340.
Question 5: What does NEC Article 358 govern?
- Rigid PVC conduit
- Electrical metallic tubing (EMT) (Correct answer)
- Intermediate metal conduit (IMC)
- Rigid metal conduit (RMC)
Correct answer: Electrical metallic tubing (EMT)
NEC Article 358 covers the installation requirements for Electrical Metallic Tubing (EMT).
Question 6: When securing nonmetallic-sheathed cable (NM) to a box, within how many inches of the box must a cable clamp or fitting be installed?
- 6 inches
- 12 inches (Correct answer)
- 8 inches
- 18 inches
Correct answer: 12 inches
NEC 334.30(B) requires NM cable to be secured within 12 inches of a box or fitting where a clamp or fitting is required.
Question 7: What is the minimum cover requirement for Schedule 80 PVC conduit installed under a residential driveway?
- 6 inches
- 12 inches (Correct answer)
- 18 inches
- 24 inches
Correct answer: 12 inches
NEC Table 300.5 requires only 12 inches of cover for rigid nonmetallic conduit (Schedule 80) under a residential driveway.
IEC Wiring Methods and Materials 2
What is the minimum bending radius for a 1-inch rigid metal conduit (RMC)?