National Electrical Code Top Ten Tips: Article 430, Motors

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. NEC 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 ou may need, depending on your specific application.
    
3. NEC Article 430.6 explains the process of determining ampacity and motor rating. It tells you which tables to use, and provides additional explanation.
    
4. NEC Article 430.7 explains what information must appear on the motor nameplate (or other markings). It provides NEC Table 430.7(B), which gives locked-rotor indicating code letters.
    
5. NEC Article 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 NEC Article 43.21 and ending at NEC Article 43.29. Pay special attention to NEC Table 430.22 (Duty cycle service).
    
6. NEC Article 430 Part III explains the requirements for motor overload protection. This begins at NEC Article 43.31 and ends at NEC Article 43.44. Keep in mind, this is motor overload protection, not circuit overload protection. You’ll find NEC Table 430.37 most useful.
    
7. NEC Article 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 NEC Article 430.51 and ends at NEC Article 430.58. You’ll find NEC Table 430.52 most useful.
    
8. NEC Article 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 begins at NEC Article 430.61 and ends at NEC Article 430.63.
    
9. NEC Article 430 Part VI and Part VII explain the requirements for motor control circuits and motor controllers. You’ll find NEC Table 430.72(B) and NEC Table 430.91 most useful.
    
10. NEC Article 430 Part XIII contains the motor-related Tables, beginning with NEC Table 420.147. As with the text, these tables do a passable job of being presented in logical order. The first four address full-load current. The last two are conversion tables for lock-rotor currents.