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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 2017 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. 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 you may need, depending on your specific application. For example, the requirements for transformers and transformer vaults are in Article 450.
     
  3. 430.6 explains the process of determining ampacity and motor rating. It tells you which tables to use, and provides additional explanation.
     
  4. 430.7 explains what information must appear on the motor nameplate (or other markings). It provides Table 430.7(B), which gives locked-rotor indicating code letters.
     
  5. 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 430.21 and ending at 430.29. Pay special attention to Table 430.22 (Duty cycle service).
     
  6. 430 Part III explains the requirements for motor overload protection. This begins at 430.31 and ends at 430.44. Keep in mind, this is motor overload protection, not circuit overload protection. You’ll find Table 430.37 very useful when working with overload units.
     
  7. 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 430.51 and ends at 430.58. You’ll find Table 430.52 very useful when working with Overcurrent Protection Devices (OCPDs).
     
  8. 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 is in Part V, which begins at 430.61 and ends at 430.63.
     
  9. 430 Part VI and Part VII explain the requirements for motor control circuits and motor controllers, respectively. You’ll find Table 430.72(B) (Minimum Rating of OCPDs) very useful.
     
  10. 430 Part XIII contains the requirements for motor control centers. It starts at 430.92 and ends at 430.99. Then with Part IX, you'll find the requirements for motor disconnects. Then you get to Part X, which provides the requirements for adjustable speed drives. There are a couple more Parts, followed by several pages of motor-related tables.

 

 

 
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