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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 550, Mobile Homes, Manufactured Homes, and Mobile Home Parks

  1. Article 550 used to distinguishe between portable and stationary appliances, now it simply defines portable appliances and leaves it to the reader to draw the obvious conclusion about appliances that aren't portable (they must be stationary) [550.2].

  2. In its vernacular, Article 550 includes "manufactured homes" when it speaks of "mobile homes;" it does not separate the two ideas the way the manufactured home industry does except in the definitions it provides [550.2]. In reality, there is not a whole lot of difference.
  3. A mobile home must comply with Article 550, even if it's not installed in a trailer park. A mobile home not intended as a dwelling unit (e.g., one used as a construction office) doesn't need to comply with the requirements in Article 550 regarding the number or capacity of circuits. [550.4].
  4. A common area of confusion is whether the supply cord permanently attaches to the mobile home box. It does not. It permanently attaches to the distribution panel board. Note that the supply cord [550.10(B)] is not the same thing as a supply feeder [550.10(A)].
  5. The attachment plug cap must meet specific criteria. You can't use just any large amperage connector [550.10(C)].
  6. The supply cord must be at least 20 feet long (down from 21 feet in earlier revisions, such as the 2011), and no longer than 36.5 ft [550.10(D)].
  7. Each mobile home must have its own disconnecting means [550.11(A)].
  8. The receptacle requirement are very similar to those for non-mobile homes, and you'll find these in 550.13.
  9. Where Article 550 discusses "grounding" in 550.16, it is referring to "bonding" in almost all instances. Before applying 550.16, carefully read the Article 100 definitions of grounding and bonding. Don't make the mistake of driving ground rods in place of required bonding connections.
  10. Beginning with 550.18 and continuing on through the end of Article 550, you find the requirements for calculating the loads, branch circuits, feeders, and service. These amend the requirements for Articles 210, 215, 220, and 230.


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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