Q. Which of the following wiring methods is the only one permitted to be installed under the roof decking in an industrial building without a minimum 1 ½-inch spacing from the bottom edge of the roof decking?

  1. Metal clad (MC) cable
  2. Electrical metallic tubing (EMT)
  3. Rigid nonmetallic conduit (RNC)
  4. Rigid metallic conduit (RMC)

Answer: D

As per 300.4(E), the only wiring methods permitted to be installed without a 1 ½-inch space between the wiring method and the roof decking are intermediate metallic conduit (IMC) and RMC.

Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at necexpert@aol.com.