Introduction to the NEC
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elcome to this course on the National Electrical Code as it applies to
Motor Control circuits, Class 1, Class 2 and Class 3 circuits.
This Guide was written specifically to address the needs of mechanical
and electrical persons doing control work.
Brief History:
he first NEC was little more than a pamphlet started by the insurance
and related industries in 1897. As early as 1881, the
first Electrical Code was a one page document written by the New York
Board of Fire Underwriters, then later in 1911 by the National Fire
Protection Association. Today's NEC
is over 1000 pages long and contains over 100 articles. Thousands of
individuals and organizations have contributed to writing the NEC.
The NEC is the most widely adopted electrical code in the world and is adopted
as law by many States and local jurisdictions in the USA.
The Purpose of the NEC.
he purpose of the NEC is the practical safeguarding of persons and property
from the hazards arising from the use of electricity as given in Section 90.1(A). Many persons doing
control wiring ask, "What are the hazards associated with low voltage control
work?" For most common low voltage circuits there are minimal hazards
from electrical shock or fire in a normal dry and nonhazardous environment.
However, if the wiring is not done according to the rules in the NEC that
require separation of low power control wiring from power and lighting
wiring,
the installation may become a source of ignition and shock. The use of incorrect insulations
is also important. Cable insulations found in the NEC have
extensive listing and substitution rules to prevent the spread of fire
and toxic products of combustion.
There are also extensive rules covering special locations or classified locations where flammable gases, vapors, combustible dusts, or ignitable filings are present. In these locations low power control circuits act as a source of ignition and raceways and cable sheaths can act as a conduit for spreading flammable gases and vapors. Additional precautions to limit the energy for circuits in classified locations often employ intrinsically safe wiring methods as covered in Article 504 of the NEC.
The General Organization of the NEC and how to read the Code
here are a set of rules that must be followed when reading and studying
the NEC, or interpretations can become vague and contradictory leading
to many arguments. Persons using the Code must learn how to apply
these rules.
The Code is divided into the introduction and nine chapters, as shown in Figure 90.3. Chapters 1, 2, 3, and 4 apply generally; Chapters 5, 6, and 7 apply to special occupancies, special equipment, or other special conditions. These latter chapters supplement or modify the general rules. Chapters 1 through 4 apply generally except as amended by Chapters 5, 6, and 7 for the particular conditions.
Chapter 8 covers communications systems and is not subject to the requirements of Chapters 1 through 7 except where the requirements are specifically referenced in Chapter 8.
Chapter 9 consists of tables that are applicable as referenced.
Informative annexes at the back of the Code book are not part of the requirements of the Code but are included for informational purposes only.
When a chapter is divided into parts, Part 1 - General applies to all the other parts that are independent of each other. When sections are referenced always read the title to the section. The section rules apply within the scope of the heading or subheading only. Also, exceptions apply only to the subsection that they follow.
Article 110, Requirements for electrical installations applies to all other Articles in the NEC.
Informational Notes are explanations only and are not mandatory rules.
Mandatory rules are worded
with "Shall." Where the word "May" is used the authority having jurisdiction
may or may not grant special permission.
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