Q. Which of the following methods for connecting grounding and bonding conductors to equipment is the only one not permitted by the NEC?

  1. listed pressure connectors
  2. exothermic welding process
  3. green-colored “tapcon” self-tapping concrete anchors drilled directly through a metal box (no threads engaged), and used to connect the grounding and bonding conductors
  4. thread–forming machine screws that engage not less than two threads in the enclosure

Answer: C

Green-colored “tapcon” self-tapping concrete anchors drilled directly through a metal box (no threads engaged), and used to connect the grounding and bonding conductors, are not intended for, nor are permitted for this use (see 250.8). The use of sheet metal screws is also not permitted for this use.

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.