COD E IN F O C U S BY CHARLES R. MILLER
Part I, General, includes Articles
110. 1 through 110. 25. Topics covered
include installation and use, listing of
equipment, voltages, conductors, wiring
methods, interrupting rating, selective
coordination, mechanical execution of
work, mounting and cooling of electrical equipment, electrical connections,
arc flash hazard warning, markings,
identification of disconnecting means,
available fault current, and lockable disconnecting means.
Part II includes Articles 110. 26
through 110. 28. While Part II contains
only three sections, two of them contain
a number of subsections. Part II contains
provisions for electrical systems rated
1,000 volts (V), nominal, or less. Prior to
the 2017 NEC, the voltage threshold for
this part was 600V, nominal, or less.
Part III contains provisions for electrical systems rated more than 1,000V,
nominal, includes 110. 30 through 110. 41.
Part IV covers tunnel installations
more than 1,000V, nominal. It also con-
tains provisions for the installation and
use of high-voltage power distribution
and utilization equipment that is portable,
mobile or both, such as substations, trail-
ers, cars, mobile shovels, draglines, hoists,
drills, dredges, compressors, pumps, con-
veyors, underground excavators, and the
like. Provisions in Part V—the last part
in Article 110—apply to installations in
manholes and other electrical enclosures
intended for personnel entry.
Enclosures for electrical installations are covered in 110. 31, which is
divided into four subsections: (A) electrical vaults, (B) indoor installations, (C)
outdoor installations, and (D) enclosed
equipment accessible to unqualified people. The provision pertains to conductors
and equipment rated over 1,000V, nominal. Section 110. 31(B) pertains to indoor
installations and is divided into two subsections. In accordance with 110. 31(B)
( 1), indoor electrical installations that are
accessible to unqualified people shall be
made with metal-enclosed equipment.
Switchgear, transformers, pull boxes,
connection boxes and other similar associated equipment shall be marked with
appropriate caution signs.
It may be necessary to refer to Article
490 when referencing requirements in
Part III of Article 110. Article 490 covers
the general requirements for equipment operating at more than 1,000V,
nominal. In accordance with 490.30,
Part III covers assemblies of switchgear and industrial control equipment
including, but not limited to, switches
and interrupting devices and their control, metering, protection and regulating
equipment where they are an integral
part of the assembly, with associated
interconnections and supporting structures (see Figure 1).
The last sentence in 110. 31(B)( 1) states
that openings in ventilated dry-type
ARTICLE 110 IN THE NATIONAL ELECTRICAL CODE (NEC), covers general
requirements for the examination and approval, installation and use, access to
and spaces about electrical conductors and equipment; enclosures intended for
personnel entry; and tunnel installations. It contains five parts.
General Installation Requirements, Part XXXII
FIGURE 1 INSTALLATIONS ACCESSIBLE
TO UNQUALIFIED PERSONS
Indoor electrical installations accessible to unqualified people shall be made
with metal-enclosed equipment [ 110. 31(B)( 1)].
Switchgear, transformers, pull boxes, connection boxes and other similar
associated equipment shall be marked with appropriate caution signs
[ 110. 31(B)( 1)].
Enclosures for electrical installations are covered in Article 110. 31, and these
provisions pertain to conductors and equipment rated over 1,000V, nominal.
P – DMH
P – DDM
T – CRM