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National Electrical Code Articles and Information

NEC Quiz: Article 425 Answers

by Mark Lamendola

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  1. There isn't one. Individual branch circuits can supply any VA or wattage of fixed resistance and electrode industrial process heating equipment [425.3].

  2. The so-called three foot rule is a myth that arises from misapplying one value from the NEC and OSHA working space tables and from ignoring the fact the appropriate value from either table is just a starting point. Another factor, such as maintenance requirements, can add to the appropriate table value. In the case of this equipment, you must comply with 110.26 and 110.34 [425.8(B)]. As the 425.(B) exception note states, there is an exception permitted. But it should be used only when there is no other choice due to conditions; it should not be used simply to gain floor space for some other business purpose.

  3. That depends upon the combustible material and the specifications of the equipment you are installing. You must follow the required (by the equipment manufacturer) spacing for that particular combination, unless the equipment is rated for direct contact with those specific combustibles [425.13].

  4. Yes, but only if it has a marked "off" position, is part of a fixed heater, and disconnects all ungrounded conductors [425.19(B)(1)(C)].

  5. Even though 425.85 says you do, the answer is no you don't. See the Article 100 definitions of grounding and bonding, and then read Article 250, Part V. What is meant here is to bond those metallic parts. As they are bonded (directly or not) to each other and to the equipment "grounding" (bonding) conductor, in the United States this method is called "grounding". But it's confusing to use that terminology because a ground connection is a connection to the dirt. The bonding connection is a low-impedance metallic path back to the source. The earth does not make a good bonding jumper. Instead of a fraction of an ohm of impedance, the earth might present thousands of ohms or more of impedance. If you draw out the many parallel circuits and apply Kirchoff's Law of Parallel circuits, you can see that a grounding connection does not remove dangerous potential but does allow current to circulate exactly where you don't want it to.

 

 

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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