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.
- 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.
- 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.
- 430.6 explains the process of determining ampacity and
motor rating. It tells you which tables to use, and provides
- 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.
- 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
- 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.
- 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).
- 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.
- 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.
- 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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