The idea behind developing the Code was to help explain how certain things work the way they do. For example: How does a GFCI work? Why can't an individual current-carrying conductor be installed in a metal raceway? Why can the protection for a 20-amp conductor feeding a motor be protected with 40-amp protection? Why can't a 15-amp single receptacle be installed on a 20-amp circuit? How can a bird rest on an energized power line and not be electrocuted? When you learn how and why elements of an electrical system work, youíll better understand the Code ó and youíll be able to easily answer these questions.
Your study plan should allow enough time to read each NEC reference at least three times. Read carefully the first time. The next time you review it should only take 10% of the first time. Try and make the Code reference interesting. Think of jobs youíve done in the past and how the Code reference applies to that job. Each time you do this it helps the reference stick in your memory. Make a final review of all references and notes on the day before the exam. The more you review, the better youíll remember and the faster youíll be able to find the answers on the day of the test.
Everyone wants to finds things quickly in the NEC, but until you become familiar with its organization, it will take some effort on your part. You can choose to use the NEC Index, or look through the Table of Contents to locate your references.
For example, what if you want to look up grounding? You wonít initially know that Article 250 concerns grounding, so the Table of Contents, which is organized by Article number (then subject), wonít be very helpful to you at first. I suggest using the Index until you know the Articles and their numbers. A few examples of Articles youĎll refer to frequently are:
Article 230, Services
Article 240, Overcurrent Protection
Article 250, Grounding
How to Read a Code Section
Letís look at how the Code is organized and what you need to understand to find a code section. What if the subject you want to research is indicated by 250.20(A)(1) in the Index? What does that mean? The numbers before the period indicate the Chapter and Article number. Articles in each chapter all begin with the chapter number where youíll find them; Article 100 is in Chapter 1, Article 200 in Chapter 2, and so on. The number after the period indicates the Section. So, weíre being sent to Section 20 of Article 250, in Chapter 2. And finally, letters and numbers in parentheses indicate Subsections.
An Article may also be broken down into Parts: I, II, III, IV, etc. Then, under each Part are the Sections which are again broken down into Subsections. The Part of an Article or Section isnít included in the Article number, but will often be included after the Article number in the Index. For example, in the Index under Grounding, youíll find Bonding, 250-V. That tells you that the subject of Bonding is covered in Part V of Article 250.
Information in a particular Part of a Section isnít necessarily related to all installations. For example, Article 110, Requirements for Electrical Installations, begins with Part I. General. Information in that Part is related to all the installations following, until you get to Part II. 600 Volts, Nominal, or Less. Information in a Part relates only to the subject covered in that Part.
Letís use Table 110.26(A)(1), Working Spaces, on page 43 of the NEC, as an example. This particular table gives the dimensions of working clearances in front of electric equipment. This information doesnít apply to all electrical installations, as youíll soon see. Looking more carefully, we find that rules 110.26 through 110.27 are within Part II of Article 110. Part II only applies to 600 Volts, Nominal, or Less, as the Part heading indicates.
Regulations for systems over 600 volts begin in Part III, Over 600 Volts, Nominal, and end at the beginning of Part IV. Table 110.34 gives information about dimensions of working space for equipment containing circuits over 600 volts.
I find it helpful to circle in red each Part heading (marked with Roman numerals: I, II, III, etc.) of every Article, and write that numeral at the top of the page. That way, when you look for a particular Part of that Article, itíll be easier to find.
Now, letís look at the Code. I decided to take a subject thatís pretty dull, the NEC, and make it as interesting as possible. Rather than starting at the beginning of the Code and going page by page, Iíll skip around in the code book and deal with various subjects, like weíre in a real classroom environment.
Every wiring system consists of three parts: the service, the feeders, and the branch circuits. The minimum size of the service entrance conductors is determined by the total volt-amps of all feeder and branch circuit loads.
There are two methods used by a utility company to deliver power to a building: overhead service drop or underground service lateral.
Overhead Service-Drop Conductors (Part II, Article 230.22)
An overhead service drop, by definition, consists of the overhead conductors from the last pole to the structure, including the connection to the service entrance conductors at the service head (see Article 100 ó Definitions).
The service entrance conductors are the conductors between the service-drop conductors and the service disconnecting means, which is located either inside or outside the building or structure. The required location of the service disconnecting means for all structures is clearly defined. It must be located at a readily-accessible location, and be as close as possible to where the service conductors enter the building. See Article 230.70(A).
Finding Information in the NEC
Using the information weíve covered so far, letís try finding the answer to a question pertaining to Article 230, Service. When youíre dealing with an electrical question, the easiest way to find the answer is to:
Find the subject of the question.
In the Index, find the word or words that best describe the subject of the question.
Finally, list the reference(s) following that word in the index on a piece of scratch paper.
Use the following breakdown to help analyze the question and find the answer:
SUBJECT ________________ INDEX ________________ SECTION ________________