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By Mike Holt
From Article 200 through 285
CHAPTER 2. WIRING AND PROTECTION
Chapter 2 provides the general rules for wiring and protection of conductors. The rules in this chapter apply to all electrical installations covered by the NECexcept as modified in Chapters 5, 6, and 7.
As you go through Chapter 2, remember the purpose of it. Chapter 2 is primarily concerned with correct installation of circuits and the means of protecting them. Every Article in the Chapter deals with a different aspect of fulfilling that purpose. This differs from the Chapter 3 purpose, which is to correctly size and install the conductors that comprise those circuits.
Chapter 1 introduced you to the NEC and provided a solid foundation for understanding the NEC. Chapters 2 and 3 (Wiring Methods and Materials) together form the heart of the NECthey form a solid foundation for applying the NEC. Chapter 4 applies the preceding chapters to general equipment. So, once again, you find yourself needing to learn the NEC in a sequential manner because each Chapter builds on the one before it. Once you've mastered the first four Chapters, you can learn the next four in any order you wish.
Article 200 Use and Identification of Grounded (neutral) Conductors
This Article contains the requirements
for identification of the grounded (neutral) conductor and its terminals. If you
go back to Article 100, you will see the grounded conductor is not the grounding
conductor. Make sure you clearly understand the difference between the two, before
you begin your study of Article 200.
Here are some things to keep in mind as you study Article 200:
Article 210. Branch Circuits
This Article contains the requirements for branch circuits, such as conductor sizing, identification, GFCI receptacle protection, and receptacle and lighting outlet requirements. It consists of three parts:
Table 210.2 of this Article identifies specific-purpose branch circuits. When people complain that the Code "buries stuff in the last few Chapters and doesn't provide you with any way of knowing," that is because they didn't pay attention to this table.
Some key items to spend extra time on, as you study of Article 210:
The rest of the material is also important. But, your mastering these key items will give you a decided edge in your ability to do work that is free of Code violations.
Article 215. Feeders
The next logical step up from the branch circuit is the feeder circuit. Consequently, Article 215 follows Article 210. This Article covers the rules for installation, minimum size, and ampacity of feeders.
One thing you'll notice is this is a very short article. This can be puzzling at first glance. It might seem feeders would just be "heavier" branch circuits, so Article 215 should just be another Article 210 but with more stringent requirements. But, this isn't the case at all.
If you go back and look at Article 210 again, you'll see it covers many permutations of branch circuits. It also devotes extensive space to dwelling area branch circuits. Dwelling areas don't have feeder circuits. A large multifamily residence building, such as a high-rise apartment building, may have feedersbut these are not in the dwelling areas.
Do you remember how much time we spent with Article 100? Here's an object lesson in the value of Article 100. Go there now and review the definitions of branch circuit and feeder circuit. Once you've done that, you will understand why Article 215 is so much shorter than Article 210.
Article 220. Branch Circuit, Feeder, and Service Calculations
This Article provides the requirements for sizing branch circuits, feeders, and services, and for determining the number of receptacles on a circuit and the number of branch circuits required. It consists of three parts:
Part I provides requirements for branch circuit calculations and for specific types of branch circuits. Part II provides requirements for feeder and service calculations, just as the title says. Part III provides some shortcut calculations you can use in place of the more complicated calculations provided in Part Iif your installation meets certain requirements. Part IV is just what it says it is.
The typical electrician is wise to focus on Parts I and II. Whether to do the optional calculations is typically a decision made by the project manager or design engineer. You need to be aware that there can be two right answers when doing the calculations because the NEC allows two different methods.
The cost of improperly applying Article 220 can be staggering. In the best of all possible worlds, the price of misapplication is just an expensive callback and some rework. In reality, the costs can easily involve catastrophic destruction and the loss of human life.
So, study Article 220 carefully. If something doesn't make sense at first, make a note of it and take a short break from your studies. Then, go back to that item and read through the explanation, using the illustration to help you understand. Your learning will really stick if you also consider the why, not just the how. A review of Article 110 will help you toward that end.
Article 225. Outside Branch Circuits and Feeders
This Article covers installation requirements for equipment, including conductors located outdoors, on or between buildings, poles, and other structures on the premises. It has two parts:
Part I provides you with a listing of other articles that may provide additional requirements, addresses some general concerns, and briefly covers conductor sizing. Then, it addresses conductor support, attachment, and clearances.
Part II addresses how many supplies you can have to a building. Then, it addresses disconnects. This includes such things as where to locate them and how to group them.
Article 230. Services
This Article covers the installation requirements for service conductors and equipment. The requirements of service conductors differ from those of other conductors. For one thing, service conductors for one structure cannot pass through the interior of another structure [230.3]. And you apply different rules, depending on whether a service conductor is inside or outside a structure. When are they "outside" as opposed to "inside?" The answer may seem obvious, but it's not. You must understand Article 430 so you can accurately make this distinction.
In fact, it's usually a good approach to start a service installation by deciding which conductors belong in the service. What you decide here will determine how you do the rest of the job. To identify a service conductor, take a close look to see if you are dealing with a service or a load side distribution point. Note that service conductors originate at the utility (service point) and terminate on the line side of the service disconnecting means (service equipment). But, feeder conductors (covered by Articles 215 and 225) originate on the load side of service equipment. Conductors and equipment supplied from a battery, uninterruptible power supply system, solar voltaic system, generator, transformer, or phase converters are not considered service conductors; they are feeder conductors.
Article 230 consists of seven parts:
Before studying the material that comes next, just read through it to get a feel for how the seven parts relate to each other. Then, go back and study it.
Article 240. Overcurrent Protection
This Article provides the requirements for selecting and installing Overcurrent Protection Devices (OCPDs). A review of the basic concept of overcurrent protection will help you avoid confusion as we move forward. You have overcurrent when current exceeds the rating of conductors or equipment. This overload can be due to overload, short circuit, or ground fault.
To protect conductors and equipment, you use OCPDs. But, OCPDs protect conductors and equipment differently.
An OCPD protects a circuit by opening when current reaches a value that would cause an excessive temperature rise in conductors. The OCPD interrupting rating must be sufficient for the maximum possible fault current available on the line-side terminals of the equipment [110.9]. You'll find the standard ratings for fuses and fixed-trip circuit breakers in 240.6. Using a water analogy, current rises like water in a tank-at a certain level, the OCPD shuts off the faucet. Think in terms of normal operating conditions that just get too far out of normal range.
An OCPD protects equipment by opening when it detects a short-circuit or ground fault. Every piece of electrical equipment must have a short-circuit current rating that permits the OCPD (for that equipment) to clear short circuits or ground faults without extensive damage to the electrical components of the circuit. [110.10]. Using a water analogy, a pipe bursts-creating a sudden rise in level-and the OCPD shuts off the supply to the pipe. Short circuits and faults are not normal operating conditions. Thus, the OCPD for equipment will have different characteristics and application than will OCPDs for conductors.
Article 240 consists of seven parts:
Part I. General
Part II. Location
Part III. Enclosures
Part IV. Disconnecting and Guarding
Part V. Plug Fuses, Fuseholders, and Adapters
Part VI. Cartridge Fuses and Fuseholders
Part VII. Circuit Breakers
Article 250. Grounding
No other Article can match Article 250 for misapplication, violation, and misinterpretation. In fact, we commonly see Article 250 violations as requirements! For example, many industrial equipment manuals require violating 250.24 violation as a condition of warranty. The manuals insist on installing an "unbonded grounding electrode." This is an electrode with no return path to the service other than the earth itself. That means the effective return path to the service is on the order of gigohms rather than the fraction of an ohm the typical NEC-compliant installation would provide. These are mutually exclusive requirements. Which way is correct?
If you apply basic physics and basic electrical theory, you can clearly see Article 250 is right and the equipment manual is wrong. And other standards agree. IEEE-142 and Soares Book on Grounding use the same physics and electrical theory as Article 250. This article is not a "preferred design specification." As with the rest of the NEC, it serves the purpose stated in Article 90.
Article 250 covers the requirements for providing paths to divert high voltage to the earth, requirements for the low-impedance fault current path to facilitate the operation of overcurrent protection devices, and how to remove dangerous voltage potentials between conductive parts of building components and electrical systems.
With the 2002 edition, this Article underwent extensive revision to better organize it and make it easier to implement. It's arranged in a logical manner, so it's a good idea to just read through it to get a big picture view-after you first to go to Article 100 and review the definitions of grounded and bonded. Then, study the Article closely so you understand the details. The illustrations will help you understand the key points.
Article 280. Surge Arresters
This Article covers general requirements, installation requirements, and connection requirements for surge arresters installed on premises wiring systems.
Surge arresters generally apply to only the supply side (line side) of the meter (280.22). Some devices are listed for use in either the line side or the supply side. Transient voltage surges are short-term deviations from a desired voltage level, of high enough magnitude to cause equipment malfunction or damage. Surge arresters are designed to reduce transient voltages present on utility power lines and other line side equipment.
A surge arrester limits surge voltages by discharging or bypassing surge current. It prevents continued flow of follow current without sacrificing itself in the process, so it can repeatedly provide the intended protection. An example of a surge arrester is a spark gap device, which discharges an overvoltage into the ground.
Article 285. Transient Voltage Surge Suppressors (TVSSs)
This Article covers general requirements, installation requirements, and connection requirements for transient voltage surge suppressors (TVSS) permanently installed on premises wiring systems. It does not apply to cord-and-plug-connected units.
TVSS devices generally apply to only the load side (285.21). Transient voltage surges are short-term deviations from a desired voltage level, of high enough magnitude to cause equipment malfunction or damage. TVSSs are designed to reduce transient voltages present on premises power distribution wiring and other load side equipment.
A TVSS is designed to shunt the current and clamp the voltage. This is a key difference between a TVSS and a surge arrester. The TVSS will clamp at a given voltage, depending on its rating vs. the actual surge current at its input terminals. This allows the TVSS to provide a more precise level of protection than a surge arrester can provide.
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