
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
3 common reasons to use purge systems
- They allow electrical enclosures to be installed in hazardous areas without the need for explosion proof enclosures.
- They recycle the air inside of an enclosure, reducing the internal temperature.
- They help reduce the effects of corrosion on components housed within the enclosure.
How does a purge system work?
Purge systems use incoming air from a supply line, solenoid valves, pressure gauges and pumps, to constantly maintain a positive pressure inside an enclosure. This prevents any flammable gases from entering the enclosure potentially causing an ignition event to occur. By maintaining a positive pressure within the enclosure, moisture and corrosive gases are also prevented from entering the enclosure and damaging components. Most purge systems will ensure that the air inside the enclosure is recycled a certain amount of times within a given time period. This air recycle function assists in maintaining a cooler temperature within the enclosure.
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.