SELECTION OF ELECTRICAL EQUIPMENT FOR HAZARDOUS AREAS

When an electrical apparatus is to be installed in areas where dangerous concentrations and quantities of flammable gases, vapors,mists, ignitable fibers, or dusts may be present in the atmosphere, protective measures are applied to reduce the likelihood of explosion due to ignition by arcs, sparks, or hot surfaces produced either in normal operation or under specified fault conditions. The following International Electrotechnical Commission (IEC) standards are relevant for the correct selection and installation of electrical apparatus in hazardous areas: ■ IEC Standard 60079-14: Electrical Apparatus forExplosive Gas Atmospheres, Part 14: Electrical Installations in Hazardous Areas (Other Than Mines) ■ IEC Standard 61241-14: Electrical Apparatus for Use in the Presence of Combustible Dust, Part 14: Selection and Installation. In this article, we discuss IEC Standard 60079-14, which was revised in 2007. The changes to the standard and the consequences of these changes for the installers and users are discussed. Special emphasis is accorded to critical components, such as flameproof cable entries and cable selection. Tests carried out by the Germany's Federal Institute of Physics and Metrology (PTB) with direct entries into flameproof enclosures using various cable types and the results are presented. It has been found practical to classify hazardous areas into zones according to the likelihood of an explosive gas atmosphere being present (see IEC Standard 60079-10 for definitions). Such classification allows appropriate types of protection to be specified for each zone. In the ATEX directive 94/9/EC, the new idea "Criteria Determining the Classification of Equipment-Groups into Categories" now defines different levels of safety for the electrical apparatus against the possibility of becoming a source of ignition. Therefore, the user can have a second selection criterion for choosing the correct product for a given application. © 2009 IEEE.