THE NEC® INTRODUCTION
The NEC® uses many technical terms and expressions. It's crucial that you understand the meanings of basic words like ground, grounded, grounding, and neutral. If you don't understand basic terms used in the Code, you won't understand the rule itself. It is not only the technical words that require close attention in the NEC®; even the simplest words can make a big difference. The word "or" can imply alternate choices for equipment, wiring methods, and other requirements. Sometimes "or" can mean any item in a group. The word "and" can be an additional requirement, or any item in a group.
Note: Electricians, engineers, and other trade-related professionals have created their own terms and phrases (slang or jargon). One of the problems with the use of slang terms is that the words mean different things to different people.
Understanding the safety-related concepts behind NEC® rules means understanding how and why things work the way they do (electrical theory). How does a bird sit on an energized power line without getting fried? Why, when we install a lot of wires close together, do we reduce the amount of current that each conductor can carry? Why can't a single current-carrying conductor be installed within a metal raceway? Why does the NEC® permit a 40 ampere circuit breaker to protect motor circuit conductors that are only rated 20 ampere? Why are bonding jumpers, sometimes required for metal raceways containing 480Y/277-volt circuits, but not for 120/240-volt circuits? If you understand why and how things work, you will have a better chance of understanding the NEC® rules.
THE NEC® LAYOUT
Contrary to popular belief, the NEC® is a fairly well organized document, although parts of it are somewhat vague. Understanding the NEC structure and writing style is extremely important to understand and use the Code book effectively.
The National Electrical Code® is organized into 12 components.
1. Chapters (major categories)
2. Articles (individual subjects)
3. Parts (divisions of an Article)
4. Sections, Lists, and Tables (Code rules)
5. Exceptions (Code rules)
6. Fine Print Notes (explanatory material, not mandatory Code language)
7. Definitions (Code rules)
8. Marginal Notations, Code changes (I) and deletions (.)
9. Table of Contents
10. Index
11. Annexes
1. Chapters. There are nine chapters and each chapter contains Articles. The nine chapters fall into four groupings:
· General Rules: Chapters 1 through 4
· Specific Rules (Hazardous locations, signs, control wiring): Chapters 5 through 7
· Communication Systems (Telephone, Radio Television, and Cable TV Systems): Chapter 8.
· Tables: Chapter 9
2. Articles. The NEC® contains approximately 138 Articles. An Article covers: a specific subject, as in the following examples:
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· Article 110 - General Requirements
· Article 250 - Grounding
· Article 300 - Wiring Methods
· Article 430 - Motors
· Article 500 - Hazardous (classified) Locations
· Article 680 - Swimming Pools
· Article 725 - Control Wiring
· Article 800 - Communication Wiring
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3. Parts. When an Article is sufficiently large, the Article is subdivided into Parts. For example, Article 250 contains ten parts, including:
· Part I. General
· Part II. Circuit and System Grounding
· Part III. Grounding Electrode System
CAUTION: The "Parts" of a Code Article are not included in the Section numbers. Because of this, we have a tendency to forget what "Part" the Code rule is relating to. For example, Table 110-34(A) gives the dimensions of working space clearances in front of electrical equipment. If we are not careful, we might think that this table applies to all electrical installations. But Section 110-34 is located in Part III Over-600 volt Systems of Article 110! The working clearance rule for under-600 volt systems is located in Part I of Article 110, in Table 110-26(A)(1).
4. Sections, Lists, and Tables.
Sections. Each actual Code rule is called a Section and is identified with numbers, such as Section 225-26. A Code Section may be broken down into subsections by letters in parentheses, and numbers in parentheses may further break down each subsection. For example, the rule that requires all receptacles in a bathroom to be GFCI protected is contained in Section 210-8(A)(1).
Note: Many in the electrical industry incorrectly use the term "Article" when referring to a Code Section.
Lists. The 2002 NEC® has changed the layout of some Sections that contain lists of items. If a list is part of a numeric subsection, such as Section 210-52(A)(2), the items are now listed as (1), (2), (3), (4), etc. instead of (a), (b), (c), (d), etc.
Tables. Many Code requirements are contained within Tables, which are a systematic list of Code rules in an orderly arrangement. For example, Table 300-50 lists the burial depths of cables and raceways.
5. Exceptions. Exceptions are italicized and provide an alternative to a specific rule. There are two types of exceptions: mandatory and permissive. When a rule has several exceptions, those exceptions with mandatory requirements are listed before those written in permissive language.
(a) Mandatory Exception. A mandatory exception uses the words "shall" or "shall not." The word "shall" in an exception means that if you are using the exception, you are required to do it in a particular way. The term "shall not" means that you cannot do something.
(b) Permissive Exception. A permissive exception uses such words as "shall be permitted," which means that it is accepted to do it in this way.
6. Fine Print Note, (FPN) [90-5]. A Fine Print Note contains explanatory material intended to clarify a rule or give assistance, but it is not Code requirement. FPNs often use the term "may," but never "shall."
7. Definitions. Definitions are listed in Article 100 and throughout the NEC®. In general, the definitions listed in Article 100 apply to more than one Code Article, such as "branch circuit," which is used in many Articles.
Definitions at the beginning of a specific Article apply only to that Article. For example, the definition of a "Swimming Pool" is contained in Section 680-4 because this term applies only to the requirements of Article 680 - Swimming Pools.
Definitions located in a Part of an Article apply only to that Part of the Article. For example, the definition of "motor control circuit" applies only to Article 430, Part F.
Definitions located in a Code Section apply only to that Code Section. For example, the definition of "Festoon Lighting" located in Section 225-6(b) applies only to the requirements contained in Section 225-6.
8. Changes and Deletions. Changes and deletions to the NEC® are identified in the margins of the 2002 NEC® in the following manner: A vertical line (I) marks changes and a bullet (e) identifies deletion of a Code rule. Many rules in the 2002 NEC® were relocated. The place from which the Code rule was removed has a bullet (e) in the margin, and the place where the rule was inserted has a vertical line (I) in the margin.
9. Table of Contents. The Table of Contents located in the front of the Code book displays the layout of the Chapters, Articles, and Parts as well as their location in the Code book,
10. Index. We all know the purpose of an index, but it's not that easy to use. You really need to know the correct term. Often it's much easier to use the Table of Contents;'
11. Annexes. There are six appendices in the 2002 NEC®.
· Annex A - Product Safety Standards
· Annex B - Ampacity Engineering Supervision.
· Annex C - Conduit and Tubing Fill Tables
· Annex D - Electrical Calculation Examples
· Annex E - Types of Construction
· Annex F - Cross-Reference Tables
FINDING THINGS IN THE CODE BOOK
How fast you find things in the NEC® depends on your experience. Experienced Code users often use the Table of Contents instead of the index.
For example, what Code rule indicates the maximum number of disconnects permitted for a service?
Answer. You need to know that Article 230 is for Services and that it contains a Part VI, Disconnection Means. If you know this, using the Table of Contents, you'll see that the answer is contained at page 81.
People frequently use the Index, which lists subjects in alphabetical order. It's usually the best place to start for specific information. Unlike most books, the NEC® Index does not list page numbers; it lists Sections, Tables, Articles, Parts, and Appendices by their Section number.
Note: Many people say the Code takes them in circles, and sometimes it does. However, this complaint is often heard from inexperienced persons who don't understand electrical theory, electrical terms, and electrical practices.
CUSTOMIZE YOUR CODE BOOK
One way for you to get comfortable with your Code book is to customize it to meet your needs. This you can do by highlighting, underlining Code rules, and using convenient tabs.
Highlighting and Underlining. As you read through this book, highlight in the NEC® book those Code rules that are important to you such as yellow for general interest, and orange for rules you want to find quickly. As you use the Index and the Table of Contents, highlight terms in those areas as well. Underline or circle key words and phrases in the NEC® with a red pen (not a lead pencil) and use a 6-inch ruler to keep lines straight and neat.
Color Coding for Branch Circuits and Feeders
120 / 208 volt, 3 phase, 4 wire, Wye system
Phase A – Black
Phase B – Red
Phase C – Blue
Neutral – White No. 6 & smaller – White / Gray only
Larger than No. 6 may be other than white
(marked per NEC 200-6)
Ground – Green (marked per NEC 250-119)
120 / 240 volt, 3 phase, 4 wire, Delta system
Phase A – Black
Phase B – Orange (wild leg) (marked per NEC 215-8)
Phase C – Blue
Neutral – White
Ground – Green (marked per NEC 250-119)
277 / 480 volt, 3 phase, 4 wire, Wye system
Phase A – Brown
Phase B – Orange (marked per NEC 215-8)
Phase C – Yellow
Neutral – Gray
Ground – Green (marked per NEC 250-119)
Number code all control and instrumentation wiring at termination points.
Formula Wheel Examples
1. What is the voltage drop of two No. 12 conductors supplying a 16-ampere load located 100 feet from the power supply? Formula: EVD = I x R, I = 16 ampere, R = 0.4 ohms (200 feet of No. 12 copper wire)
(a) 6.4 volts (b) 12.8 volts (c) 1.6 volts (d) 3.2 volts
2. What is the resistance of the circuit conductors when the conductor voltage drop is 7.2 volts and the current flow is 50 ampere?
(a) 0.14 ohm (b) 0.3 ohm (c) 3 ohm (d) 14 ohm
3. What is the power loss in watts for a conductor that carries 24 ampere and has a voltage drop of 7.2 volts?
(a) 173 watts (b) 350 watts (c) 700 watts (d) 2,400 watts
4. What is the current flow of a 10 kW heat strip rated 240 volts, single-phase?
(a) 35 ampere (b) 38 ampere (c) 42 ampere (d) 60 ampere
5. The formulas listed in the formula wheel apply to .
(a) DC currents only
(b) AC Single-phase
(c) a and b
(d) none of these
6. When working any formula, the key to getting the correct answer is following these four simple steps:
Step 1: > Know what the question is asking.
Step 2: > Determine the knows of the circuit or resistor.
Step 3: > Select the formula.
Step 4: > Work out the formula calculation.
(a) True (b) False
7. The total resistance of two No. 12 copper conductors 150 feet long is 0.6 ohm and the current of the circuit is 16 ampere. What is the power loss of the conductors in watts per hour?
(a) 50 watts per hour (b) 150 watts per hour (c) 300 watts per hour (d) 600 watts per hour
8. What is the conductor power loss in watts for a 120-volt circuit that has a 3 percent voltage drop and carries a current flow of 12 ampere? The load operates 24 hours per day, 365 days each year. ,
(a) 43 watts (b) 86 watts (c) 172 watts (d) 722 watts
9. What does it cost per year (24 hours per day, 365 day per year at 8.6 cents per kW) for the power loss of a conductor? The No. 12 copper conductor resistance is 0.3 ohm and the current flow is 12 ampere.
(a) $32.55 (b) $13.10 (c) $130.50 (d) $140.21
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