With the NEC 505<\/strong>, the internationally accepted classification of potentially explosive atmospheres into three zones each for gases\/liquids and dusts was introduced in the United States.<\/p>\n\n Potentially explosive areas\u2014known as Ex zones, hazardous<\/em> areas<\/em>, or classified locations<\/em> \u2014are classified according to their level of hazard in both the United States and Europe. However, for a long time, only a two-class<\/strong> or two-division<\/em> classification system<\/strong> was used in the United States. It was not until 1996 that Article 505 of the National Electrical Code introduced the three-zone classification<\/strong>, as applied, for example, in the EU under the ATEX Directive 1999\/92\/EC<\/strong>. Since then, the following zones have been distinguished. <\/p>\n\n Article 505 classifies potentially explosive areas into three zones\u20140, 1, and 2 (Ex zones)\u2014based on the frequency or duration of the explosion hazard<\/strong>. In addition, a distinction is made based on whether the air contains flammable liquids (mists, vapors), gases, or solids. If solids<\/strong> are present, the zone number is prefixed with a 2 (i.e., zones 20, 21, and 22). Thus, there are a total of six Ex zones<\/strong>. <\/p>\n\n If an explosive atmosphere occurs only rarely and for short periods<\/strong>, the affected area is classified as Zone 2 or 22<\/strong>. \u201cRarely and for short periods\u201d refers to a period during which the risk of explosion occurs in less than 50 percent of operating time<\/strong> and<\/em> lasts for less than 30 minutes per year<\/strong>. Conversely, this means that even if an explosive atmosphere is expected for only 5 minutes per year, the affected area is already classified as an Ex zone. <\/p>\n\n In Zones 1 or 21<\/strong> as well, an explosive atmosphere is expected for less than 50 percent of the operating time<\/strong>, but for a total of more than 30 minutes<\/strong>.<\/p>\n\n According to NEC 505, all areas in which an explosive atmosphere frequently<\/strong> occurs during normal operation are classified as Zone 0 or Zone 20<\/strong>. According to the standard definition, \u201cfrequently\u201d means the presence of an explosive atmosphere for more than half of the operating time<\/strong>. In practice, these zones primarily include vessels and piping filled with explosive substances. <\/p>\n\n \t\t Our experts are here to help you, whether you need a quick answer or detailed information. <\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\tNEC 505: Explosion Protection in the United States<\/h2>\n\n
Ex Zones According to NEC 505<\/h2>\n\n
Rare: Zones 2 and 22<\/h3>\n\n
Occasionally: Zones 1 and 21<\/h3>\n\n
Common: Zones 0 and 20<\/h3>\n\n
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