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

by Mark Lamendola

Based on the 2020 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. What's really going on is the application of motors is complex and Article 430 must necessarily reflect that. 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. This list is by no means complete and all you need for installing a motor. For example, the raceway requirements are in Chapter 3 (not referenced in this table). The table covers other Articles that have a bearing on the Article 430 requirements.
  3. 430.6 explains the process of determining ampacity and motor rating. It tells you which tables to use, and provides additional explanation. It takes up less than a full page, but it is very important. Rather than gloss over it, dedicate time to studying it carefully. Study it enough that you can explain it to another person without having to read it as you explain.
  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. This is aimed at manufacturers, but it also helps the installer to know what to expect on the nameplate and how to make sense of it. For example, the nameplate on one motor has a locked rotor code of D and the nameplate on a similar motor has a locked rotor code of S. Which motor will draw 4 times more current per horsepower with a locked rotor than the other motor? The answer is in that table.
  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). Did you notice that overload protection is separated from short circuit and ground fault protection? That's what makes motor circuits different from other types of circuits.
  8. Part V explains the requirements for feeder short circuit and ground fault protection. The idea here is to protect the feeder circuit conductorsr against overcurrent due to short circuits. This has nothing to do with protecting the motor from an overload. This begins at 430.61 and ends at 430.63.
  9. 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. Part VIII contains the requirements for motor control centers (MCCs). It starts at 430.92 and ends at 430.99.
  10. In Part IX, you'll find the requirements for motor disconnects. Part Xh provides the requirements for adjustable speed drives. Part XI provides additional requirements that apply to motors over 1000V, nominal. Part XIII provides "grounding" requirements, but what is really meant here is "bonding" requirements. You do not ground utilization equipment, you bond it. Finally, Part XIV provides a series of useful tables.