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National Electrical Code Top Ten Tips: Article 280 -- Surge Arresters

by Mark Lamendola

Please note, we do quote from copyrighted material. While the NFPA does allow such quotes, it does so only for the purposes of education regarding the National Electrical Code. This article is not a substitute for the NEC.

These are the 10 NEC Article 280 items we deem most important, based on the pervasiveness of confusion and the potential costs of same.

  1. NEC Article 280 addresses surge arresters while NEC Article 285 addresses transient voltage surge suppressors (TVSSs). These are not the same, though they both provide surge protection.
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  2. Surge arresters apply to (in most cases) just the supply side (line side) of the meter (280.22). TVSS devices apply to just the load side (285.21). Some devices are listed for use in either location, but typically surge protection devices are designed for use in only one or the other.

  3. Surge protection devices (SPDs) reduce potentially damaging short-duration spikes on data networks, cable lines, phone lines, and other power or control lines connected to electrical equipment. They are not a substitute for lightning protection--they address voltage levels that lightning protection does not, and therefore are complementary to it.

  4. The general hierarchy is this: lightning protection (service), TVSS (service and feeders), surge arrester (feeder and branch circuits), point of use surge protection (provided by plug-in devices, UPS systems, line conditioners, and so on).

  5.  When you use a surge arrestor, you must connect it to each ungrounded conductor. The logic here is pretty obvious.

  6. Requirements differ between circuits of less than 1,000V and those of 1,000V or over.

  7. You can put surge arrestors indoors or outdoors. It simply is not true that the NEC prohibits locating them outdoors.

  8. Surge arrestor wiring has a minimum size. Do not apply the ampacity tables or make your wiring match that of the rest of the system if doing so causes you to be below the minimums.

  9. Connecting your surge arrestor to a ground rod driven into the dirt is not sufficient. The electricity is always trying to get back to the source--that's why electricity works. You must use one of the four types of "ground sources" specified in Article 280. If you don't understand what these are--and most people do not--refer to Article 250.

  10. A surge arrester is essentially useless without good grounding and bonding.

Check out this grounding case history!

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How the NEC is arranged

  1. The first four Chapters of the NEC apply to all installations.
  2. Article 90 precedes Chapter One, and establishes the authority of the NEC.
  3. Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
  4. Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
  5. Chapter 8 provides the requirements for communications systems.
  6. Chapter 9 provides tables.
  7. The appendices provide mostly reference information.
  8. Appendix D contains examples that every NEC user should study.

Try your NEC moxy:

  • Do you know the difference between bonding and grounding? Hint: Look in the NEC, Article 100.
  • Does the NEC refer to grounding incorrectly in any of its articles? Yes! So be careful to apply the Article 100 definitions. Don't ground where you should bond.
  • When doing motor load calculations, which Article covers hermetic motors? Answer: While Article 440 covers the application of hermetic motors, it does so only by amending Article 430 because hermetic motors are a special case of motors. For motor load calculations, refer to Article 430.
  • Does the NEC provide a voltage drop requirement? Yes! It does so in a special case, which is Article 648 Sensitive Electronic Equipment. But for general applications, it does not provide a requirement; it merely provides a recommendation in a couple of FPNs.
  • Take our Code Quizzes.

Remember other applicable codes, rules, standards, and references:

  • OSHA's electrical worker safety rules.
  • IEEE standards.
  • NETA standards.
  • NFPA standards.
  • International Codes (if applicable to the installation).
  • State Codes (if the state has them).
  • Local ordinances and permit requirements.
  • Local fire codes.
  • Manufacturer requirements or guidelines.
  • Customer security requirements.
  • Industry standards.
  • Your company's own internal standards, practices, and procedures.
  • Engineering drawing notes.

 

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