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Residential Electrical Inspector (CAE)
Lesson 2
NEC Layout and Terminology
(Based on the 2014 OESC)
Updated: January 2017
The NEC consists of a Table of Contents,
general information, (9) Chapters, Informational
Annexes and an index. The Chapters are
broken into individual Code Articles. Code Article
have specific information relating to an
installation requirement. These requirements
may specify a product, location, or Table. An
electrical installation may have several code
articles related to the installation.
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3
The NEC starts in Article 90 with language
related to the applicability of the document and
the layout of the document itself. Article 90 also
provides language related to terminology such
as “shall and shall not”.
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The NEC is set up in a manner where
Chapters 1-4 apply throughout the document.
Chapters 5-7, supplement or modify Chapter
1-4 requirements and Chapter 8 stands alone.
Chapter 9 consists of Tables that are applied
when performing certain calculations such as
box fill, raceway fill, voltage drop and
determining circular mils of conductors. The
Index is found in the back of the document.
Using the NEC Index along with Henry’s Key
Word Index help with looking items up quickly.
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Section 90.3
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In order to determine the applicable codes
governing an electrical installation, the NEC is
used in a manner where multiple chapters and
code sections work in conjunction with each
other. For example, the installation of a service
requires looking in Articles 110, 230, 250, 300,
310 and 344. These code sections are found
in Chapters 1, 2 and 3 respectively.
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Utility
Weather head Service point
Straps
Hub
Bonding
jumper
Main
bonding
jumper
Neutral
Service-entrance
conductors
Service disconnect
Grounding
electrode
conductor
GEC installation
Grounding
electrode
Mast
Service Terms
$
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230.24
230.54 230.26
344.30
250.92
250.92 250.28 250.24
T310.15(B)(16)
230.90
250.64
250.66
250.68
250.52
230.28
Service
$
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Throughout the NEC in addition to Article, there
are definitions that are specific to a code
article. The definitions found in Article 100 are
those that appear in more than one code article.
Definitions specific to a code article are usually
found in .2 of the Article. For example,
definitions related to PV are found not only in
Article 100 but in Section 690.2. Definitions are
used to ensure that everyone is on the same
page when applying a specific code section.
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ARTICLE 100
Definitions
Scope. This article contains only those definitions
essential to the proper application of this Code. It
is not intended to include commonly defined
general terms or commonly defined technical
terms from related codes and standards. In
general, only those terms that are used in two or
more articles are defined in Article 100.
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Example:
240.2 Definitions
250.2 Definitions
320.2 Definition
Many articles utilize the .2 for definitions
specific to that article but several articles do not
have a definition unique to the article so .2 may
be used for other code requirements.
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12
.2 Example:
240.2 Definitions
Current-Limiting Overcurrent Protective
Device. A device that, when interrupting currents
in its current-limiting range, reduces the current
flowing in the faulted circuit to a magnitude
substantially less than that obtainable in the
same circuit if the device were replaced with a
solid conductor having comparable
impedance.
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Index Example
AC and DC conductors in same enclosure,
300.3(C)(1), 725.48
AC armored cable see Armored cable (Type AC)
Access and working space; see also Working
space
Audio signal processing, amplification, and
reproduction equipment, 640.46
Elevator machine room, 620.71
Induction and dielectric heating equipment,
665.22
Manholes, 110.72, 110.73, 110.75
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Non-metallic sheathed cable (NM cable) is
often referred to as “Romex or rope”. “Romex”
is a trade name and means the same as “NM
Cable” covered in Article 334.
Generally, NM cable consists of a cable with a
PVC outer jacket, it is not the wire insulation,
an inner paper that encloses individual
conductors. The power conductors are
insulated and the grounding conductor is bare
and inside a paper sleeve.
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Common Terms
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16
The NM cable is designated by size and
number of insulated conductors. For example,
12/2 is a cable that has two insulated
conductors and one uninsulated conductor
used for grounding. Cable outer jacket colors
help determine the most common conductor
sizes, white is generally used with #14, yellow
with #12 and orange with #10. Grey or Black is
used with conductors #8 and larger.
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18
A service consists of the main electrical panel
where there is from 1 to 6 circuit breakers installed.
The service may be supplied through a utility meter
or be part of an assembly called a meter main.
The term “service” is often used to describe
providing power to appliances, building, equipment,
etc. In reality a “service” is the location where
utility drops off and the customer ownership starts.
When speaking to an electrician, the term “service”
should be clarified to make sure everyone is
speaking about the same thing.
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19
A service has a
main breaker or
up to 6 breakers
to disconnect
power. There is
a connection to
the earth and to
the metal
enclosure. A
service will have
the neutral and
ground bus tied
together. of 52
20
Service-entrance cable (SE cable) is another
term used frequently. The SE cable runs from
the meter socket enclosure to the service
panel. The cable lands on the line or supply-
side of the main circuit breaker(s). A circuit
breaker or fuse is used as a means of
protection for downstream conductors against
an overload, short-circuit or ground-fault
condition. The fuse or circuit breaker has a
line (supply) side and a load side. SE cable is
considered to be unfused.
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Service disconnect
and enclosure with
cover removed.
Finish your service
inspection at the
service disconnect
enclosure.
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(2) Service-
Entrance
conductors and
(1) neutral
conductor from
meter base
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Bottom half of
service
enclosure.
Neutral bus
Ground bus
Main bonding
jumper
Tie bar
(250.24A1)
GEC
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Overhead supplied
service
Service point
Weather-head
Drip loop
Mast
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Grounding
electrode
conductor
Grounding
electrode
Ground clamp
Mud ring for
accessibility
26
Meter socket
enclosure
SE cable
Service
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27
Meter socket
enclosure
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Meter Inspection
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This meter
type is
typical of
what is
seen at the
start of the
service
inspection.
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Always
assume that
the
meter/servic
e is
energized
and treat it
that way.
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Meter base with
cover removed.
Start the service
inspection at
the meter base.
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Overhead
Fed Service
1)Start your
inspection
ensuring
power is off
and
removing
cover
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Overhead
Fed Service
2) Verify that
the
conductors
are the
correct size
and tight
310.15(B)(7)
110.14(A)
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Overhead
Fed Service
3) Verify that
the mast is
tight to the
fitting and
threads are
fully engaged
and tight to
the enclosure
250.92(A)
250.12
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Overhead Fed
Service
4) If anti-oxidant
is required on
connections
verify use
110.3(B)
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Service Panel Inspection
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5) Is service
disconnect
at nearest
point of entry
of service-
entrance
conductors?
230.70(A)(1)
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6) Remove cover,
verify that the
power is off
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7) Verify that the
SE conductors
terminate in a
disconnecting
means, and have
overcurrent
protection either as
part of the
disconnect or
immediately
adjacent to the
disconnect.
230.90, 230.91
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8) Verify that the main
bonding jumper is
installed and bonding the
ground bus to the
enclosure
250.24(A)(1), 250.28
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9) Verify that the tie bar
tying the neutral bus to
the ground bus is
installed. This
connection in
combination with the
MBJ ensures that all of
the metal enclosures
are bonded together
250.24(A)(1), 250.92
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10) Verify that the
grounding electrode
conductor is installed,
properly sized and the
connection is tight.
250.66, 250.64,
250.24(D)
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11) Verify that a
proper grounding
electrode is installed,
a proper clamp is
used with an
attached GEC and
the connection is
accessible.
250.52, 250.64,
250.66, 250.68
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12) Verify that an
intersystem bonding
jumper for limited
energy system
bonding has been
installed
OESC 250.94
Grounding and Bonding are used interchangeably
and have two distinctive functions. Grounding and
Bonding are one of the most misunderstood
sections of the code and care must be taken to
ensure everyone is on the same page.
Conductors are often referred to as “wiring”.
Receptacles are often referred to as “outlets”.
A concrete encased electrode is often referred to
as a “ufer”.
The term “can” means enclosure.
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Cable can mean anything from the line voltage to
the low voltage or door bell wiring.
A knockout is an area of a metal electrical box that
is removed for the installation of an electrical
connector. Knockouts are either concentric or
eccentric.
If a hole is oversized, reducing washers and/or
bushings are used. The use of these devices may
result in a need to meet additional bonding
requirements to maintain metal to metal contact
between metal enclosures or equipment.
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49
Concrete encased
electrode (UFER)
Grounding
electrode conductor
(GEC)
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Be prepared for pushback from some folks. The
training program is not popular with some and as
inspectors, we can improve this image by being
professional, concentrating on the big picture and
doing the right thing. Electrical can be over-whelming
and with the frequent code changes, keeping up with
current codes is a challenge.
A student must spend time studying on their own to
understand the layout of the NEC and OESC. Ask lots
of questions.
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One of the best things a student can do, is to
create a contact list of trusted contacts. When
out in the field, unusual installations or
circumstances can pop up that make you doubt
your knowledge. The contact list allows you to
bounce issues, ideas and installations of others
that may have more experience or knowledge
such as another inspector, building official or at
the state level.
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Lesson 2 Homework
Review Articles 100 and 110.
Lesson 1 and Lesson 2 Questions
Will be sent to you
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