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2005 NEC Changes Summary Articles 500 through 501

Chapter 5 Special Occupancies

Chapter 5, which covers special occupancies, is the first of four NEC chapters that deal with special topics.

[ NOTE: There are no illustrations included in this newsletter ]

What exactly is a "special occupancy?" It's a location where the physical facility or use of the physical facility creates specific conditions that require additional measures to ensure the "safeguarding of people and property" mission of the NEC put forth in Article 90.

The NEC groups these logically, as you might expect. Here are the general groupings:

  • Environments that pose additional hazards. Articles 500 - 510. Examples include Hazardous (classified) Locations.
  • Specific types of facilities that pose additional hazards. Articles 511 - 516. Examples include motor fuel dispensing facilities, aircraft hangars, and bulk storage plants.
  • Facilities that pose evacuation difficulties. Articles 517 - 525. Examples include hospitals, theaters, and carnivals.
  • Motion picture-related. Articles 530 and 540.
  • Specific types of buildings. Articles 545 - 553. Examples include park trailers and floating buildings.
  • Marinas and boatyards. Article 555.
  • Temporary installations. Article 580.

Most people struggle to understand the requirements for Special Occupancies, mostly because of the narrowness of application. However, if you study the illustrations and explanations here, you will clearly understand them.

ARTICLE 500 Hazardous (Classified) Locations, Classes I, II, and III, Divisions 1 and 2

A hazardous location is an area where the possibility of fire or explosion can be created by the presence of flammable liquids or gases, combustible dusts, or ignitable fibers or flyings. Sparks and/or heated surfaces can serve as a source of ignition in such environments.

Article 500 provides a foundation for applying Article 501 (Class I Locations), Article 502 (Class II Locations), Article 503 (Class III Locations), and Article 504 (Intrinsically Safe Systems)-all of which immediately follow Article 500. It also provides a foundation for applying Articles 510 - 516.

Before you apply any of the articles just mentioned, you must understand and apply Article 500. It's a fairly long and detail article. But don't worry; we'll help you master the concepts.

A Fire Triangle (fuel, oxygen and ignition) often illustrates this concept. Figure 500-1
Fuel - Flammable liquids or gases, combustible dusts, and ignitible fibers or flyings.
Oxygen - Air and oxidizing atmospheres.
Ignition - Electric arcs or sparks, heat producing equipment such as luminaires and motors, conductor insulation, failure of transformers, coils or solenoids, as well as sparks caused by metal tools dropping on a metal surface.

  • New exception reduces the five thread engagement requirement for factory cut female threads to 4½, to allow more US products to align with the worldwide IEC standard. The five threads engaged rule was previously contained in 501.4(A)(1).

ARTICLE 501 Class I Locations

If enough flammable liquids or gases are present to produce an explosive or ignitable mixture, you have a Class I location. Examples of such locations include fuel storage areas, certain solvent storage areas, grain processing (where hexane is used), plastic extrusion where oil removal is part of the process, refineries and paint storage areas.

Article 500 contains a general background on hazardous (classified) locations as well as describing the differences between Class I, II and III locations and the difference between Division 1 and Division 2 in each of the three classifications. Figures 501-1 and 501-2

Article 501 contains the actual Class I, Division 1 and Division 2 installation requirements, including wiring methods, seals, and specific equipment requirements.

A Class I hazardous (classified) location is an area where flammable gases or vapors may be present in quantities sufficient to produce an explosive or ignitible mixture.

  • A scope was added to this article, and many of the sections were renumbered and rearranged for easier use.
  • Text revisions clarify that when a conduit leaves a Class I, Division 2 location to an unclassified location, the required boundary seal isn't required to be explosionproof, but it must be identified for the purpose.

Mike Holt's Comment: If you desire more information about any of the above changes, be sure to order my Changes book and/or library (Video/DVD).

13a. NEC Code Changes Textbook
Mike Holt’s Illustrated Changes to the NEC 2005 textbook is here! So, get ready now!

A new Code cycle has begun and it’s that time again to adapt to the 2005 NEC. Don’t let the scale of this change intimidate you. With Mike Holt’s Illustrated Changes to the NEC 2005, you’ll be up-to-speed in no time. Nearly 5,000 changes were proposed for the 2005 NEC! Over 225 of them will have a significant impact on designing, installing and inspecting electrical systems. Mike takes you through these changes, which he considers to be of critical importance. You’ll be able to easily gauge how these changes will impact your work and apply them instantly. This 120-page comprehensive full-color textbook includes 198 color illustrations for reference. Subjects include: General Requirements, Circuits and Protection, Grounding versus Bonding, Wiring Methods, Equipment for General Use, Special Occupancies, Special Equipment, Special Conditions, and Limited Energy and Communications Systems.

Why does Mike’s book give you an edge? It’s because of the extra effort put forth to organize these changes in an easy-to-follow manner. Each change includes:

  • Cross references to other related Code requirements to help you develop a better understanding of how the Code rules relate to one another.
  • Background information for each change along with explanations, which are delivered in Mike’s trademark style… easy-to-understand.
  • Author’s Comments – this is basically Mike speaking to you directly about something that he feels should be brought to your attention.
  • Full-color detailed graphics to reinforce those difficult concepts and provide instant understanding.

Product Code: 05BK
ISBN: 1-932685-27-8
Pages: 120
Illustrations: 198

Table of Contents
Sample Pages
Sample Graphic


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