
Hazardous Location Enclosures

Electrical enclosures are designed to house industrial components and to protect them from the surrounding environment. They are also designed to protect operators from electric shock. They come in many different shapes, sizes and materials. Some things to consider when selecting the proper enclosure would be the number of components housed inside and what material and rating will provide the appropriate protection.
Hazardous location enclosures are specifically designed to isolate electrical components from hazardous locations. Hazardous locations are classified as areas where there is the possibility of explosion or fire because of the presence of ignitable or combustible gases, vapors, liquids, fibers or dust. Electrical equipment can be a potential source of ignition through sparks, equipment failure and high temperatures. Hazardous location enclosures are constructed to eliminate the potential for ignition of the atmosphere.
Enclosure pressure purging is a protection method used to remove any internal explosive dust or gases through a purging process, followed by a pressurization of the enclosure with a protective air or inert gas. This results in a positive internal pressure which keeps any external explosive dust or gases from entering the enclosure.
The National Electrical Manufacturers Association (NEMA) has devised a rating system to set performance standards for electrical enclosures. Manufactures follow these universal standards when making their electrical enclosures and label them accordingly. It is important to understand that NEMA has a special rating class for hazardous locations.
Type 7 designed to contain an internal explosion without causing an external hazard. For indoor use in classified hazardous locations defined in NFPA 70. Deals with vapors and gases.
Type 8 designed to prevent combustion through the use of oil-immersed equipment. For either indoor or outdoor use in hazardous locations defined in NFPA 70.
Type 9 designed to prevent the ignition of combustible dusts. For indoor use in hazardous locations defined in NFPA 70
Type 10 designed to contain an internal explosion without causing an external hazard. Used in mining applications and meets the requirements of the Mine Safety and Health Administration.
Subcategories
These are some of the National Electrical Manufacturers Association (NEMA) standard designations for hazardous locations:
- Class 1 Div 1 Group C - Certified to provide a degree of protection against atmospheres typically containing chemicals such as ethylene, diethyl ether, or cyclopropane all or some of the time under normal operating conditions.
- Class 1 Div 1 Group D - Certified to provide a degree of protection against atmospheres typically containing compounds such as propane, gasoline, hexane, butane, naphtha, acetone, toluene, or isoprene all or some of the time under normal operating conditions.
- Class 2 Div 1 Group E - Certified to provide a degree of protection against atmospheres typically containing metal dusts, such as magnesium, all or some of the time under normal operating conditions.
- Class 2 Div 1 Group F - Certified to provide a degree of protection against atmospheres typically containing carbonaceous dusts, such as carbon black, coal dust, coke dust, or charcoal, all or some of the time under normal operating conditions.
- Class 2 Div 1 Group G - Certified to provide a degree of protection against atmospheres typically containing non-conductive dusts, such as flour, starch, grain, wood or plastic, all or some of the time under normal operating conditions.
These descriptions are derived from directives from the EU designed to protect employees by defining levels of protection of areas that pose explosion risks due to elements in the immediate atmosphere:
- ATEX Directive 94-9-EC Zone 1 - Rated for use in an environment where exposure to an atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapor or mist is likely to occur occasionally (between 10 and 1000 hours/year) in normal operation.
- ATEX Directive 94-9-EC Zone 2 - Rated for use in an environment where exposure to an atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapor or mist is likely to occur occasionally (less than 10 hours/year) in normal operation.
- ATEX Directive 94-9-EC Zone 21 - Rated for use in an environment where exposure to an atmosphere in the form of a cloud of combustible dust in the air is likely to occur occasionally (between 10 and 1000 hours/year) in normal operation.
- ATEX Directive 94-9-EC Zone 22 - Rated for use in an environment where exposure to an atmosphere in the form of a cloud of combustible dust in the air is not likely to occur in normal operation but, if it does occur, will only persist for a short period (less than 10 hours/year).
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FAQ
Is a NEMA 4x enclosure explosion proof?
An enclosure with a NEMA 4x rating is corrosion proof. Explosion proof enclosures must have a NEMA 7 or NEMA 8 rating.