National Electrical Code Articles and Information

National Electrical Code Top Ten Tips: Articles 670 and 675 -- Machinery

The NEC has two Articles that provide requirements for machinery:

1. Article 670, Industrial Machinery.
2. Article 675, Electrically Driven or Controlled Irrigation Machines

With that spread of Article numbers, there's room for adding other categories of machinery some day. It's anybody's guess what those might be, but there are four slots available.

It's interesting that this series comes right after Article 669, which is a very short article providing requirements for electroplating equipment. Since electroplating is an industrial process, it would have been more logical to include it as Part III of Article 670 (with the existing text being divided into Part 1 General and Part II for the remainder). Then, various subcategories of industrial machinery could have their own Parts in Article 670 if those end up needing specific requirements developed.

1. Article 670 provides the requirements for conductors and overcurrent protection for industrial machinery, in addition to the requirements presented in Chapters 1 - 4.
    
2. Article 675 provides the requirements for irrigation machines, plus their branch circuits and controllers, in addition to the requirements presented in Chapters 1 - 4.
    
3. Industrial machines must have a permanently attached nameplate that provides five specific types of information [670.3].
    
4. The size of the supply conductor  to an industrial machine must be such that the ampacity is at least 125% of the FLC rating of all resistance heat loads plus 125% of the FLC rating of the highest rated motor plus the sum of the FLC of all other connected motors and apparatus that might operate at the same time [670.4(A).]
    
5. A machine is an individual unit and must have an individual disconnect [670.4(B)].
    
6. To interconnect enclosures on the structure of an irrigation machine, you have to use cable meeting specific criteria [675.4(A).
    
7. For irrigation machines, don't count signal and control wires for the purpose of adjusting ampacity [310.15(B)(3)(a) based on the number of conductors [675.5].
    
8. The main controller used to start and stop the irrigation machine must have an equivalent continuous current rating at least that which is specified in 675.7(A) or 675.22 and a horsepower rating at least as large as the value from Table 430.251(A) and 430.251(B) [675.8]. But a listed molded switch doesn't need a horsepower rating.
    
9. If you have several motors on an irrigation machine, you have to meet the three conditions in 675.10. That is, if the machine is protected at 30A or less, 600V nominal or less.
    
10. The grounding and bonding requirements for irrigation machines are in 675.12, 657.13, and 675.14. Please review the definitions of grounding and bonding in Article 100 before proceeding, and please review Article 250, Parts I, II, III, IV, VI, and VII.

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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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