NEMA - National Electrical Manufacturer Association
National Electrical Code – PC Models only
National Electrical Code (NEC) defines hazardous locations as those areas "where fire or explosion
hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable
fibers or filings."
A substantial part of the NEC is devoted to the discussion of hazardous locations. That is because
electrical equipment can become a source of ignition in these volatile areas. The writers of the NEC
developed a short-hand method of describing areas classified as hazardous locations. One of the purposes
is to explain this classification system. The National Electrical Code classifies hazardous locations in
three ways: TYPE, CONDITION, and NATURE.
National Electrical Manufacturer Association (NEMA) ratings are standards that are useful in defining the
types of environments in which an electrical enclosure can be used. The NEMA rating system is defined
by the National Electrical Manufacturer Association, and frequently signifies a fixed enclosure's ability to
withstand certain environmental conditions.
NEMA 7: Indoor use in locations classified as Class I, Division 1, Groups A, B, C or D hazardous
locations as defined in the National Electric Code (NFPA 70) (Commonly referred to as explosion-proof).
Class I Locations: According to the NEC, there are three types of hazardous locations. The first type of
hazard is one created by the presence of flammable gases or vapors in the air, such as natural gas or
gasoline vapor. When these materials are found in the atmosphere, a potential for explosion exists, which
could be ignited if an electrical or other source of ignition is present. The Code writers have referred to
this first type of hazard as Class I. Therefore, a Class I Hazardous Location is one in which flammable
gases or vapors may be present in the air in sufficient quantities to be explosive or ignitable. Some typical
Class I locations are:
• Petroleum refineries, and gasoline storage and dispensing areas
• Dry cleaning plants where vapors from cleaning fluids can be present
• Spray finishing areas
• Aircraft hangars and fuel servicing areas
• Utility gas plants
• Operations involving storage and handling of liquefied petroleum gas or natural gas
All of these are Class I - gas or vapor - hazardous locations and all require special Class I hazardous
location equipment.
Class II Locations: The second types of hazard listed by the National Electrical Code are areas made
hazardous by the presence of combustible dust. These areas are referred to in the Code as "Class II
Locations" as finely pulverized material, suspended in the atmosphere and can cause as powerful an
explosion as one occurring at a petroleum refinery. Some typical Class II locations are:
• Grain elevators
• Flour and feed mills
• Plants that manufacture, use or store magnesium or aluminum powders
• Producers of plastics, medicines and fireworks
• Producers of starch or candies
• Spice-grinding plants, sugar plants and cocoa plants
• Coal preparation plants and other carbon handling or processing areas
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