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
- Temporary installations. Article
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
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.
Comment: If you desire more information about any of the above changes, be
sure to order my Changes book and/or library (Video/DVD).
NEC Code Changes Textbook
Holts Illustrated Changes to the NEC 2005 textbook is here!
So, get ready now!
A new Code cycle
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Why does Mikes
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- Cross references
to other related Code requirements to help you develop a better
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information for each change along with explanations, which
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Comments this is basically Mike speaking to you directly
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