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National Electrical Code Articles and Information

Based on the 2017 NEC

by Mark Lamendola

National Electrical Code Top Ten Tips: Article 547, Agricultural Buildings

  1. Article 547 takes up about three full pages, making it among the shortest of NEC articles. However, the agricultural buildings it covers are still subject to the first four Chapters of the NEC. Article 110 is especially important in this regard.
     
  2. Despite being one of the shortest articles in the NEC, Article 547 has one of the longest statements of scope. That's because the main concern is ignition from either:
    (A) Excessive dust and dust with water [547.1(A)], or
    (B) Corrosive atmosphere [547.1(B)].
     
  3. The equipotential plane [547.2] is an important concept in agricultural buildings. It's a bonding system that eliminates difference of potential. Don't confuse this with "ground" which means a connection to the earth [100].
     
  4. You are limited on permissible wiring methods. You can use Types UF, NMC, copper SE cables, jacketed Type MC cable, RNC, LFNC, or other cables or raceways suitable for the location. And you must use approved termination fittings [547.5(A)]. For areas with excessive dust or dust with water, you can use the wiring methods of Article 502, Part II.
     
  5. Where an equipment grounding conductor is installed underground within a location falling under the scope of Article 547, it shall be insulated [547.5(F)].
     
  6. All 125V, single-phase, 15A and 20A receptacles must be GFCI-protected if installed outdoors, in reas having an equipotential plane, in damp or wet locations, or in dirt confinement areas for livestock [547.5(G)].
     
  7. You must install a site-isolating device at the distribution point where two or more structures are supplied from the distribution point [547.9(A)(1)]. At the site-isolating device, you must connect the system grounded conductor (e.g., neutral) to a grounding electrode system via a grounding electrode conductor [547.9(A)(5)].
     
  8. Equipotential planes indoors. They must be installed in confinement areas with concrete floors where the metallic equipment is located, if said equipment may become energized and is accessible to livestock [547.10(A)(1)].
     
  9. Equipotential planes outdoors. They must be installed in concrete slabs where metallic equipment is located, if said equipment is energized and is accessible to livestock [547.10(A)(2)].
     
  10. Equipotential planes must be connected to the electrical grounding system, via a solid copper bonding conductor at least 8AWG [547.10(B)].

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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