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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.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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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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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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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

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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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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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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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