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.
- 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.
- NEC Table 430.5 provides a cross-reference to other NEC Articles
that ou may need, depending on your specific application.
- NEC Article 430.6 explains the process of determining ampacity and
motor rating. It tells you which tables to use, and provides
additional explanation.
- 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.
- 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).
- 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.
- 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.
- 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.
- 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.
- 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.
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