Many wonder what exactly an explosion proof enclosure is and what the difference is between the classifications. In this article we outline what explosion proof means, the testing involved, and the different classifications. With out further adieu, let’s take a look!
What is explosion proof?
According to the National Electric Code (NEC) explosion proof equipment is “equipment enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas or vapor within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby.” What this definition explains is that “explosion proof” doesn’t mean it can withstand exterior explosions, but it can prevent an internal explosion from causing a larger blast.
To be considered explosion proof the device must withstand an internal explosion and it also must work to prevent the spread of the explosion to the surrounding atmosphere. This is commonly accomplished by the use of closures and joints built into the device. Although the device may be damaged, they are designed to not allow the explosion to reach the hazardous atmosphere.
Also to meet the NEC’s standards the equipment must meet temperature requirements. The operating temperature cannot be greater than the lowest ignition temperature of the dusts or gases in the atmosphere where the equipment will be installed.
Testing explosion proof enclosures
In order to get the explosion proof label, a nationally recognized testing laboratory, such as the Underwriters Laboratories, will test the product based on the standards set by the National Fire Protection Association (NFPA) and other international standards. To determine if a product is in compliance of these standards, you can look for certain marks including UL, ETL, CSA, and others. Products that do not have these marks may not meet the NEC requirements. In order to be tested by these laboratories, a prototype of the product must be sent to them for inspection.
Explosion proof classifications
Since electrical equipment can cause explosions in certain atmospheres, there are different classifications of hazardous locations divided into classes, divisions, and groups to identify the specific hazards. The below chart illustrates the different classifications defined by the National Electric Code. It should be noted that this chart is a summary, for exact requirements please contact the NEC.
National rating agencies and the American National Standards Institute all adhere to these NFPA definitions of hazardous areas. Class I is made up of combustible gas and liquids, Class II is made up of combustible dust, and Class III combustible fibers. Each is then further subdivided into groups (as shown in the chart) and all classes include two divisions. Division I covers electrical equipment directly exposed of the material of a specific group in an explosion atmosphere. Division II covers electrical equipment in a properly vented direct exposure or an explosive atmosphere only when fallout or an accident occurs.
Whether you are just researching or are ready to buy, AccuTherm can help you customize your own explosion proof enclosures that will fit your needs. Talk to one of our experts today at 573-735-1060 or visit us at www.accutherm.com.