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National Electrical Code Articles and Information

Based on the 2020 NEC

by Mark Lamendola

National Electrical Code Top Ten Tips: Article 551, Recreational Vehicles and Recreational Vehicle Parks. Part 2.

  1. Article 551 amends the Chapter Three wiring methods; it does not replace them. Where Article 551 is silent, Chapter 3 requirements apply [551.47(A)].
     
  2. You can't mix metallic and nonmetallic wiring methods. That is, use nonmetallic raceway (or non-metallic sheathed cable) if you use nonmetallic boxes [551.47(C)].
     
  3. In these wiring systems, no bend can have a radius of less than five wire (or cable) diameters [551.47(H)].
     
  4. Any prewiring must meet the applicable part of 551.47(Q), (R), or (S). This includes air conditioning and generator systems.
     
  5. Any luminaire installed over a bathtub or in a shower stall must be GFCI-protected [551.53(B)]. The newer integrated LED fixtures make this rule unnecessary for such fixtures, but the NEC still does not provide an exception for them.
     
  6. Do not ground interior electrical equipment. Where 551.55 speaks of "grounding," it means "bonding." If you review these terms in Article 100, you will see the terminology error when you read the requirements. Make sure you bond, not ground, interior equipment.
     
  7. Bonding conductors for non-current carrying metal parts must be at least 8AWG [551.56(C)]. While it would be "nice" to use a larger conductor, keep in mind that if a number 8 eliminates differences in potential a larger conductor can't eliminate more differences (there aren't any) or eliminate them faster. If reliability is the concern, use bonding jumpers around raceway connections instead of simply upsizing bonding conductors.
     
  8. You will find the requirements for RV Parks in Article 551, Part VI. Calculate loads per 551.73.
     
  9. Don't use the grounded conductor (neutral) as an equipment bonding conductor [551.76(D)]. This applies to all circuits, not just RV ones. The reason is the neutral (which is, at these voltage levels, the grounded conductor) carries the unbalanced current back to the source. It does not provide a low impedance path for eliminating differences of potential. Confusion here can result in a lethal touch shock.
     
  10. Don't connect the grounded conductor to a grounding electrode on the load side [551.76(E)]. Actually, don't connect anything on the load side to any ground electrode; such a connection serves no electrical purpose.

 

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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