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National Electrical Code Articles and Information

National Electrical Code Top Ten Tips: Article 409 -- Industrial Control Panels

by Mark Lamendola

Based on the 2021 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 409 items we deem most important, based on the pervasiveness of confusion and the potential costs of same.

  1. Any control panel operating at 1000V or less must comply with Article 409 [409.1].
  2. An industrial control panel can have control circuits, power circuits, or both.
  3. Quite a few other Articles apply to these panels, in addition to the specific requirements of Article 409. See Table 409.3. For example, if the industrial control panel is for a rail crane, Article 610 also applies.
  4. Base the ampacity of the supply conductor on the sum of three items [409.20]:
    A. 125% of the full-load current rating of all resistance heating loads (combined).
    B. 125% of the full-load current rating of the highest rated motor.
    C. Sum of the full-load current rating of all the other motors (and apparatus) that may be operating at the same time.
  5.  Provide overcurrent protection per Article 240, Parts I, II, and IX [409.21].
  6. You can put overcurrent protection ahead of the panel or inside it [409.21(B)].
  7. You do not ground an industrial control panel. You bond it [409.60]. Grounding means a path to the earth, which is fine for lightning protection. It does nothing for reducing dangerous differences of potential because it is not a low-impedance path between metallic objects or to the equipment grounding conductor or back to the source.
  8. Don't use industrial control panels as junction boxes or as any kind of feed-through system. Circuits that are not part of the panel must be routed around it, not through it. While this is not explicitly stated in Article 409, it is implicitly stated. In addition to the fact it is a control panel (read that name again), the marking requirements in 409.11 make this fairly obvious.
  9. Control cabinets have wire bending and spacing requirements. Those nice 90 degree bends for 5V systems do not belong inside a typical industrial control panel. And if wiring is voluminous, simply dumping it in a gutter or routing it inside plastic wrap isn't the solution. See 409.104 for requirements.
  10. Spacing requirements are critical. See Table 430.97(D) [409.106].


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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