Q. A surge protective device (i.e., surge arrester or TVSS) shall be permitted for which of the following?

  1. On circuits exceeding 1kV.
  2. On ungrounded systems, impedance grounded systems, or corner grounded delta systems where not listed specifically for use on these systems.
  3. Where the rating of the surge protective device (SPD) is less than the maximum continuous phase-to-ground power frequency voltage available at the point of application.
  4. Where the rating of the SPD is equal to or greater than the maximum continuous phase-to-ground power frequency voltage available at the point of application.

Answer: D

As per 285.3, the only use(s) permitted is where the rating of the SPD is equal to or greater than the maximum continuous phase-to-ground power frequency voltage available at the point of application … or on ungrounded systems, impedance grounded systems or corner grounded delta systems where listed specifically for use on these systems.

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.