Most of the following material
was extracted from "Understanding the National Electrical Code"
Article 90 - Introduction
Article 90 is the introduction of the
NEC. This is a short article and we recommend that you read all of it.
Section 90-1. Purpose,
starts off by telling you that the purpose of the Code is the practical safeguarding of
persons and property from hazards arising from the use of electricity.
Section 90-2. Scope describes
what is "covered" and "not covered" in detail. The FPN (meaning Fine Print Note) following
90-2(b)(5) sums up what is covered.
Section 90-3. Code Arrangement
is very important for understanding the "structure" of the Code. Understanding the structure
of the Code is the key to finding answers and information quickly. It tells you that this
Code is divided into the Introduction (Article 90) and 9 chapters.
Chapters 1, 2, 3, and 4
are the "general rules" of the Code. Chapters 1, 2, and 3 are very general while Chapter
4 is more specific in that it deals with "Equipment" such as flexible cords, appliances,
motors, etc. These chapters apply to everything in the Code except as modified in
Chapters 5, 6, and 7
apply to "special" (specific) occupancies, equipment, or conditions. These chapters
modify the general rules of chapters 1 through 4. The basic rule of thumb is that
Chapters 1, 2, 3, and 4 apply except as modified by Chapters 5, 6, and 7.
Chapter 8 covers
communications systems and is independent of the other chapters except where they
are specifically referenced.
Chapter 9 consists
of Tables and Examples. This chapter is very helpful for everyone that uses the Code
on a regular basis. The tables have a variety of applications and have a lot of specific
information about conductors.
Chapter 1. General
As the name implies, this chapter has
very general information about the NEC. If the average person using the NEC read Article
90 and Chapter 1, he or she would gain a good understanding of the Code book structure,
terminology (definitions), and general assumptions (such as "copper" unless otherwise
specified) which would make the other chapters much easier to use and understand.
Article 100 - Definitions
has definitions of many terms that apply to the NEC. It is very important to understand
the meanings of these terms and this article should be read thoroughly.
Article 110 - Requirements for
Electrical Installations is another very important article for understanding the
NEC. This article should be read, particularly "Part A. General."
I want to point out three things that
will be extremely helpful in using and understanding the NEC. Turn back to the Table of
Contents and go to "Chapter 1. General." Under "100 Definition", you will see "Part
A. General" and "Part B. Over 600 Volts".
(1) With the exception of
a few articles, all the articles in the NEC are broken down into "Parts" which
are like sub-headings. When you are trying to find an answer or specific information,
the Part headings can direct you to an area of an article that applies. Many people
using the NEC will read an entire article trying to find something. Taking advantage
of the Part headings can save you a lot of time.
(2) The information following
a Part heading applies to that part only. ALWAYS know which "Part" you
are under so that you will know the main subject the information applies to.
(3) Many articles have a
Part called "Over 600 Volts, Nominal." If you are trying to find information
about "over 600 volts," it is usually located at the end of an article in its
own part. If you are trying to locate information on "up to 600 volts", you don't
need to look in these areas. Since we are in Chapter 1, both Article 100 and 110
have an "Over 600 Volts Part".
One more important point about "Parts"
is Part A. General. If you thumb through the Table of Contents, you will see that
many article have this. Part A. General is very helpful for understanding the article.
It contains general information that applies to the article as a whole.
Chapter 2. Wiring and Protection
NEC Chapter 2 is a "General Rules" chapter
as applied to "Wiring and Protection" of conductors. The rules in this chapter apply everywhere
in the NEC except as modified (such as in Chapters 5, 6, and 7). Along with Chapter 3,
it can be considered the "heart" of the Code. Many of the everyday applications of the
NEC can be found in this chapter.
Article 200 - Use and Identification
of Grounded Conductors covers the requirements for the identification of terminals,
grounded conductors in premises wiring systems, and identification of grounded conductors.
You should understand ALL the definitions in the NEC but the "grounded, grounding, neutral,
etc." terms should be very carefully studied and understood.
The general rule is "All premises wiring
systems shall have an identified grounded conductor." A grounded conductor is usually
the system neutral or white wire. This requirement is repeatedly listed in the NEC. Be
very careful not confuse groundED conductors with groundING conductors.
Article 210 - Branch Circuits
contains the requirements for determining the placement of receptalces as well
as the requirements for circuits.
Section 210-3 Classification
tells us that the rating (or setting) of the overcurrent protection device is the
rating of the branch circuit. For example, a 20 ampere breaker with a No. 10 wire
rated 30 amperes is a 20 ampere branch circuit. The words "rating of the branch circuit
(or feeder)" can be found all over the NEC. This rating is the value or setting of the
overcurrent protection device.
Also, 15, 20, 30, 40, and 50 amperes
are the STANDARD branch circuit sizes. This does NOT apply to individual branch circuits
which supply only one utilization equipment. An example of a utilization equipment would
be an electric water heater, which under certain conditions could have a 25 ampere overcurrent
Article 220-Branch - Circuit
and Feeder Calculations is used as the basis for many of our Code Calculations
Chapters. This article covers the requirements for most of the calculations of branch-circuits,
feeders, and service conductor sizes in residential, commercial, and industrial occupancies.
Section 220-2 Voltages
states that unless otherwise specified, 120, 120/240, 208Y/120, 480Y/277, 480, and 600
volts are the nominal system voltages for calculations. For our NEC calculation students,
assume 120/240, unless otherwise specified.
Article 230 - Services
covers service conductors and equipment for control and protection of services and their
installation requirements. Mike has a great seminar on Services and Meter Rooms.
Diagram 230-1 is very helpful in determining which Part of Article 230 you need
to refer to in order to find information.
Section 230-42 Size and Rating
states that Article 220 is used in calculating service size and minimum rating requirements.
If the size calculated in Article 220 is smaller than the minimum rating, then minimum
ratings stipulated in 230-42 would be used.
Article 240 - Overcurrent Protection
is the first line of defense against the potential of electricity to cause damage to life
and property. Proper sizing and application of overcurrent protection devices is critical
for every system.
Article 250 - Grounding
is one of the largest, most important, and least understood articles in the NEC. As specified
in Section 90-1(a), safety is the key element and purpose of the NEC. Proper grounding
and bonding is essential for maximum protection of life and property. If overcurrent protection
is considered the first line of defense, grounding could be considered the last line of
Chapter 3. Wiring Methods and Material
NEC Chapter 3 is a "General Rules" chapter
as applied to "Wiring Methods" and "Material" and is generally related to wiring such
as raceways, cables, junction boxes, cabinets, etc. The rules in this chapter apply everywhere
in the NEC except as modified (such as in Chapters 5, 6, and 7). Along with Chapter 2,
Chapter 3 can be considered the "heart" of the Code.
If you turn to the NEC Table of Contents,
and review the Chapter 3 listings, the articles are generally grouped.
Go to Articles 318 through 344. All
of these articles (except for 331) are related to specific types of conductors and cables.
Go to Articles 345 through 362. All
of these articles are specific types of raceways. These are followed by Articles 364 and
365 (Busways and Cablebus) which are raceways with conductors for assembly.
The rest of the articles (370 to the
end of Chapter 3) are equipment associated with wiring.
Article 300 - Wiring Methods,
"Section 300-1. Scope" tells us that Article 300 applies to ALL wiring installations.
The exceptions that follow list several articles that have their own wiring methods. Throughout
the rest of the Code, the rules (sections) of Article 300 will apply except where specified,
which is usually in Chapters 5, 6, 7, and 8. If you flip through Article 300 and read
the bolded section and subsection titles, you will see very general types of requirements.
Article 305 - Temporary Wiring
is more specific and lists rules for temporary wiring methods which may be less stringent
than normal wiring methods.
Article 310 - Conductors for
General Wiring, along with Article 300, are the two "general use" articles in
Chapter 3 that most electricians use on a daily basis. Article 310 covers the general
requirements for conductors and their type designations, insulation, markings, mechanical
strengths, ampacity ratings, and uses. These requirements do not apply to conductors that
form an integral part of equipment such as motors and appliances.
Section 310-5. Minimum Size of
Conductors and Table 310-5, list No. 14 Copper as the minimum conductor
size for 0 through 2000 volts. This is, of course, a general rule and there are
many exceptions listed following Section 310-5. The point I want to make here has to do
with LOCAL codes. What is your answer to the following question, "What is the
minimum conductor size permitted by the NEC for COMMERCIAL loads?" Most people answer
this question with No. 12 AWG Copper. Even if I show them Section 310-5, they still
say No. 12. The correct answer is No. 14 AWG copper. There are many LOCAL
building codes that require a minimum of No. 12 in commercial buildings. If your job requires
the use of electrical codes, it is your responsibility to know the local codes as well
as the NEC. Another important point is that some areas around the country do not adopt
the current version of the NEC. There are places in the U.S. that still use the 1984 version
of the NEC as the basis for approval of plans and inspections. Remember, it is your responsibility
to know which codes apply to your area.
Section 310-15. Ampacity.
In Section 310-15(a), ampacities for conductors rated 0 to 2,000 volts, are listed in
Tables 310-16 through 310-19. There are the tables that apply to Article 220 calculations
and are the tables used by electricians, architects, and engineers. Tables 310-69 through
310-84 are for 2,001 through 35,000 volts and do not apply to the average person using
Table 310-13 is a very
informative table. The second column "Type Letter" alphabetically lists the common use
conductor insulation types most of us are familiar with. On the 4th page of this table
is the conductor type "THW." The double and triple obelisk () and () listed with
THW tell you that there are notes that could apply; these notes should always be read
when looking up information. For example, the double obelisk note () says that if you
see THW with the suffix "/LS" (THW/LS), that the insulation meets the requirements for
"flame-retardant, limited smoke." The 4th column, "Application Provisions," lists information
for each insulation type. Using THW as an example, this column tells us that even though
THW is "75ēC in wet and dry locations", it is rated 90ēC for use in "Special applications
within electric discharge lighting equipment."
Table 310-16 is one of
the most used tables in the NEC. It lists the ampacity ratings (current carrying capacity)
of the most commonly used conductors. These are continuous load ratings for conductors
(see definition of "Ampacity" in Article 100). As with most tables in the NEC, the notes
associated with the table should always be considered when using that table. In this case,
the Notes to Ampacity Tables of 0 to 2000 Volts, located after Table 310-19,
are very important for understanding how to use Tables 310-16 through 310-19.
NOTE: There are too many
applications and uses for this Table (and associated notes) to be covered in this
workbook. We have many products available that cover the use and application of Table
310-16 in detail. Contact our office for additional information.
Article 370 - Outlet, Device,
Pull and Junction Boxes, Conduit Bodies and Fittings is another article that has
numerous applications for the average person using the NEC. It contains information about
the number of conductors permitted in boxes as well as how to size junction boxes. It
also contains the requirements for supports and mounting equipment as well as many other
NOTE: There are too many
applications of this chapter to be covered here in detail. Contact our office for
Chapter 4. Equipment for General Use
NEC Chapter 4 is a "General Rules" chapter
as applied to "General Use Equipment." Although the term "General" is used in the name
of the chapter, it deals with specific equipment in a general application. The rules in
this chapter apply everywhere in the NEC except as modified (such as in Chapters 5, 6,
Article 400 - Flexible Cords
and Cables and Article 402 - Fixture Wires each have a Table similar
in nature to Table 310-13. You should be able to find general information about any conductor
or cable in the NEC in one of these three tables (Tables 310-13, 400-4, 402-3). The notes
related to these tables should always be reviewed when indicated.
Article 410 - Lighting Fixtures,
Lampholders, Lamps, and Receptacles deals a lot with lighting and little with
receptacles. This article contains Parts A through R. Part L is the only "receptacle"
section. When looking up information in this Article, the part headings in the table of
contents are very helpful.
Article 422 - Appliances
contains specific requirements for common appliances. It has a lot of information about
cord and plug requirements. Section 422-14. Water Heaters should be carefully
read because many electricians are sizing conductors to water heaters incorrectly. Most
branch circuit calculations are contained in Article 220, but Article 422 should be consulted
for other requirements.
Article 430 - Motors, Motor Circuits,
and Controllers is a very important exam preparation chapter. We have several
products devoted to this subject. Diagram 430-1 (FPN) is very helpful for determining
which "Part" of Article 430 you need to use. Many people using the NEC have a difficult
time with sizing the conductors and overcurrent protection to motors because they try
to apply "general" rules. Article 430 has many exceptions to the general rules, and sizing
conductors and overcurrent protection should be done using Article 430 requirements.
Article 450 - Transformers and
Transformer Vault (Including Secondary Ties). For most electricians, transformers
are perhaps the most intimidating of all subjects. This introduction cannot begin to explain
the requirements because of all the possible variations. We have lots of products available
on this subject. Keep in mind that a transformer is a device. As with all devices it has
to have protection and be grounded, and that is what most of the requirements of Article
Chapter 5. Special Occupancies
NEC Chapter 5 is a "Specific Locations"
chapter. Where Chapters 1, 2, and 3 apply throughout the code, and to residential and
commercial occupancies in general, Chapter 5 pertains to common locations that have special
conditions to consider.
Chapters 1 through 4 apply except where
modified in Chapters 5, 6, and 7, with Chapter 8 being its own article.
Articles 500 through 517 have conditions
that can be considered as hazardous in nature. Articles 500 through 504
cover the requirements for electrical equipment and wiring for all voltages in locations
where fire or explosion hazards may exist due to flammable gasses or vapors, flammable
liquids, combustible dust, or ignitible fibers or flyings. Articles 511 through
517 are specific types of hazardous occupancies, such as gas stations and anesthesia
areas in health care facilities.
Article 500 - Hazardous (Classified)
Locations breaks down and categorizes hazardous area requirements and basically
describes and defines those requirements.
Articles 501, 502, and 503
list the specific wiring methods and materials for Class I, II, and III locations.
NOTE: Mike has an excellent
lecture on this subject that breaks down the requirements in this area of the NEC
into easy to understand language.
Article 504 - Intrinsically Safe
Systems was new in the 1990 NEC. It was previously ANSI/ISA RP 12.6 1987. The
installation requirements of this type of system were moved to the NEC. "Intrinsically
Safe Systems" are low-energy wiring components.
Article 517 - Health Care Facilities
applies to all types of health care facilities. This article targets "areas" that have
special requirements. For example, hospitals, doctors offices, business and administrative
offices, kitchens, and cafeterias would be wired according to the requirements of Chapters
1 through 4. Specific areas such as examining rooms, operating rooms, X-ray areas, patient
care areas, etc. have special requirements listed in Article 517. As with many articles
in the NEC, there are several definitions listed (Section 517-2) which apply to this article
Article 518 - Places of Assembly
applies to buildings or portions of buildings designed or intended for the assembly of
100 or more persons. Section 518-2 lists (but does not limit) several types of occupancies
where this article applies. Several of the Articles following 518 are for specific places
Article 550 - Mobile Homes and
Mobile Home Parks is broken down into three (3) Parts. Part A. General
is mostly definitions that apply to this article. Part B. Mobile Homes applies
to the power cord, as well as all wiring methods and materials within and on the mobile
home, plus calculations. Part C. Services and Feeders applies to the park in general
and the individual services on the lots. Miscellaneous buildings such as recreation and
meeting rooms, or common laundry facilities fall under the regular requirements of Chapters 1
Chapter 6. Special Equipment
NEC Chapter 6 covers the requirements
for common special or "specific" equipment. Most of the equipment in this chapter is a
"group" or "system." The equipment can be single objects, such as signs; but, most of
the equipment is part of another structure, such as an elevator or overhead crane.
Chapter 6 modifies the general rules
of Chapters 1 through 4 as necessary for the individual equipment. This could also be
stated as, Chapter 1 through 4 requirements apply except as modified by the Chapter 6
Most of the articles in this chapter
are short and very specialized. For exam purposes, these are the easiest articles to find
answers for. For general use, these chapters are often used as a guide when working with
the type of equipment listed here.
Many of the articles in this chapter
have other documents listed that are related to the subject of that article. For example,
Article 610 - Cranes and Hoists, Section 610-1 Scope, (FPN) lists ANSE B-30,
Safety Code for Cranes, Derricks, Hoists, Jacks, and Slings. In Article 620 - Elevators,
etc., Section 620-1, (FPN) lists ANSI/ASME A17.1-1987, Safety Code for Elevators and Escalators.
It is your responsibility to know if these other documents are necessary for you to do
the job properly.
Remember, the NEC is only one volume
of the NFPA documents. Appendix A of the NEC has some NFPA documents listed that have
extracts in the NEC. Section 90-3, Paragraph 4 states that these extracts are identified
by the superscript letter "x" and identified in Appendix A. Better in Article 90 section?
The last point I want to make about
Chapter 6 is that several of the articles contain calculations for some of the special
equipment concerning wire size, feeder loads, etc. Always check these articles for special
requirements and calculations.
Chapter 7. Special Conditions
NEC Chapter 7 can be thought of as a
"special power" chapter. It contains the requirements for emergency and standby systems,
signaling systems, plus a few other "different" power systems.
Article 700 - Emergency Systems
pertain to systems that are essential for safety to human life. These systems are often
comprised of backup power for emergency power and lighting. This article covers the requirements
for the installation of emergency systems where required by other codes or laws. It does
not specify where emergency systems are to be installed. See NFPA 101, Life Safety Codes
for where emergency systems are required and the locations of emergency or exit lights.
The FPN's after 700-1 list other documents related to this subject.
Article 701 - Legally Required
Standby Systems are systems intended to provide electrical power to aid in fire
fighting, rescue operations, control of health hazards, and similar operations. See Section
The requirements for legally required
standby systems are similar to those for Emergency Systems. When normal power is lost,
legally required systems are required to come on in 60 seconds or less, and the
wiring can be mixed with general wiring. Emergency systems are required to come
on in 10 seconds or less, and the wiring is completely separated from the general wiring.
Article 702 - Optional Standby
Systems are those whose failure could cause physical discomfort, or serious interruption
of an industrial process, damage to process equipment, or disruption of business. See
Section 702-2 FPN.
Article 725 - Class 1, Class
2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits covers remote-control,
signaling, and power-limited circuits that are not an integral part of a device or appliance.
See Section 725-1 (FPN). This Article covers signaling type systems such as burglar alarms
and coaxial wiring associated with the interconnection of electronic data processing and
computer equipment not within a data processing room as covered in Article 645. It doesn't
cover the interconnection of such equipment that is grouped together in the same area.
It covers the wiring leaving the group of equipment to other devices in the same room
or elsewhere within the building. The 1990 NEC rearranged Articles 725, 760, 770, 800
and 820 to have similar formats. You will see the similarities as you study these articles.
A Signaling Circuit is any electrical
circuit which supplies energy to an appliance or device that gives a visual and/or audible
signal. Examples are doorbells, fire or smoke detectors, and fire or burglar alarms.
A Remote Control Circuit is any
circuit which has as its load device the operating coil of a magnetic motor starter, a
contactor, or relay. These circuits control one or more other circuits. Low voltage relay
switching of lighting and power loads can be a remote-control circuit.
Power-Limited Circuits are circuits
used for functions other than signaling or remote-control, but in which the source of
the energy supply is limited in its power (volts x amps) to specified maximum levels.
Low voltage lighting using 12 volt lamps in fixtures fed from 120/12 volt transformers,
is a typical power-limited circuit application.
Class 1 systems include all
signaling and remote-control systems which do not have the special current limitations
of Class 2 and 3 systems.
Class 2 and 3 systems are those
in which the current is limited to certain specified low values by fuses or circuit breakers,
and by supply transformers which will deliver only small currents, or by other approved
means. All Class 2 and 3 circuits must have a power source with power-limiting characteristics
as described in Tables 725-31(a) and (b), in addition to overcurrent protection.
Article 760 - Fire Protective
Signaling Systems covers the installation of wiring and equipment of fire protective
signaling systems operating at 600 volts, nominal, or less. Examples of this type of system
could include fire alarm, guard tour, sprinkler waterflow, and sprinkler supervisory systems.
Documents used in close association with this type of system would be NFPA 71, NFPA 72A,
NFPA 72B, NFPA 72C, NFPA 72D, NFPA 72E, NFPA 72F, and NFPA 74.
NOTE: We have NFPA Fire
Codes workbooks. Contact our office for additional information.
Chapter 8. Communications Systems
NEC Chapter 8 covers communications
systems and is independent of the other chapters except where they are specifically referenced
Article 800 - Communication Circuits
covers telephone, telegraph (except radio), outside wiring for fire and burglar alarms
and similar central station systems, and telephone systems not connected to a central
station system, by using similar types of equipment, methods of installation, and maintenance.
Article 810 - Radio and Television
Equipment covers radio and television receiving equipment and amateur radio transmitting
and receiving equipment, but not equipment and antennas used for coupling carrier current
to power line conductors.
Article 820 - Community Antenna
Television and Radio Distribution Systems covers coaxial cable distribution of
radio frequency signals typically employed in community antenna television (CATV) systems.
Chapter 9. Tables and Examples
NEC Chapter 9 has two distinct sections.
Part A. Tables and Part B. Examples.
Part A - Tables is often
used by electricians, engineers, and architects for information about conductors. All
the tables in this section are related to conductors and conduits in some form.
It is very important to understand all
the "Notes" involved with the Chapter 9 Tables. At the beginning of Chapter 9, Part A,
are several notes and a FPN. These are called "Notes to Tables." These notes should
be reviewed when using Chapter 9 tables.
Table 1 Percent of Cross Section
of Conduit and Tubing for Conductors (except fixture wires) is the table that
Tables 3A, B, and C are based on. Most of us are familiar with the "40 percent fill" factor,
which is based on 4 or more conductors (not lead-covered). Tables 4 through 8 are used
for calculating the number of conductors in conduit or tubing. Most of the Notes to
Table 1 are related to these calculations.
Tables 4 through 8 give
nominal sizes of conduits, tubing, and conductors for calculation purposes. It is important
to point out that these sizes are "averages only" and many variations are possible. There
are variations in sizes between different manufacturers of electrical equipment.
Table 8 Conductor Propertiesgives the
sizes and number of strands for conductors without their insulation (bare conductors).
It also gives the DC resistances for copper and aluminum wire at 75ēC. The notes to this
table state that any variations, such as coated strands, and temperature will change the
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Services and Overcurrent Protection, Grounding and Bonding, Conductors, Cables and Raceways,
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