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.
- 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.
- 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.
- 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.
- 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.
- 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). 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.
- 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.
- 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.
- 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.