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National Electrical Code Articles and Information

National Electrical Code Top Ten Tips: Article 430 -- Motors

by Mark Lamendola

Based on the 2011 NEC

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 430 items we deem most important, based on the pervasiveness of confusion and the potential costs of same.

Article 430 is arguably the most misunderstood and misapplied area of the National Electrical Code. The same claim can be made for Article 250 (grounding) and Article 310 (ampacity). Article 430 is the largest article in the National Electrical Code, and it’s complex. Our intent here is to help clear up some of the mystery, but a true understanding requires dedicated study.

  1. NEC Article 430.1 provides the scope of this Article. As with previous revisions of the NEC, this Article begins with a "road map" of what Parts affect which aspect of the motor system. Consistently, people have complained that Article 430 is mind-boggling and complex. In reality, the application of motors is complex. NEC Article 430 is about as close to a design manual as the NEC gets, and it does a remarkable job of providing the required information efficiently—but, you must start at this point. If you follow the design trail right in order—Part I, Part II, Part III and so on, you should be successful.
     
  2. NEC Table 430.5 provides a cross-reference to other NEC Articles that ou may need, depending on your specific application.
     
  3. NEC Article 430.6 explains the process of determining ampacity and motor rating. It tells you which tables to use, and provides additional explanation.
     
  4. NEC Article 430.7 explains what information must appear on the motor nameplate (or other markings). It provides NEC Table 430.7(B), which gives locked-rotor indicating code letters.
     
  5. NEC Article 430 Part II explains how to size the motor circuit conductors, which is an area rife with confusion and error. Follow Part II methodically, starting with NEC Article 43.21 and ending at NEC Article 43.29. Pay special attention to NEC Table 430.22 (Duty cycle service).
     
  6. NEC Article 430 Part III explains the requirements for motor overload protection. This begins at NEC Article 43.31 and ends at NEC Article 43.44. Keep in mind, this is motor overload protection, not circuit overload protection. You’ll find NEC Table 430.37 most useful.
     
  7. NEC Article 430 Part IV explains the requirements for branch short circuit and ground fault protection. The idea here is to protect the branch circuit conductors, the motor control apparatus, and the motor against overcurrent due to short circuits. This has nothing to do with protecting the motor from an overload. This begins at NEC Article 430.51 and ends at NEC Article 430.58. You’ll find NEC Table 430.52 most useful.
     
  8. NEC Article 430.61 explains the requirements for feeder short circuit and ground fault protection. The idea here is to protect the feeder circuit conductors, the motor control apparatus, and the motor against overcurrent due to short circuits. This has nothing to do with protecting the motor from an overload. This begins at NEC Article 430.61 and ends at NEC Article 430.63.
     
  9. NEC Article 430 Part VI and Part VII explain the requirements for motor control circuits and motor controllers. You’ll find NEC Table 430.72(B) and NEC Table 430.91 most useful.
     
  10. NEC Article 430 Part XIII contains the motor-related Tables, beginning with NEC Table 420.147. As with the text, these tables do a passable job of being presented in logical order. The first four address full-load current. The last two are conversion tables for lock-rotor currents.

 

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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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