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To prevent dust explosions, electrical equipment in Class II hazardous locations must have special construction features that meet rigid performance criteria. Dust-ignition-proof, dust-tight, and intrinsically safe are types of constructions used.
Underwriters Laboratories (UL) has developed construction and performance standards for these types of equipment. UL's hazardous location equipment test lab is a specially designed facility that provides separation of dust and explosion testing areas from laboratory personnel working areas. The lab has two dust test chambers for conducting dust penetration and dust blanket temperature tests. After each test setup is completed, testing is controlled remotely to protect lab personnel in case of a dust explosion. Testing is conducted using either grain or magnesium dust. Intrinsically safe equipment undergoes spark ignition tests with a specially constructed switching mechanism.
This paper describes Class II hazardous locations, types of protection used for equipment, and how electrical equipment tests are performed.
dust, dust-ignition-proof, dust-tight, electrical equipment, hazardous locations, intrinsically safe
Assistant managing engineer, Underwriters Laboratories Inc., Northbrook, IL