Revision of IEEE Std 303-1991 This recommended practice applies to the application and installation procedures of auxiliary devices in or on electric rotating machines that are employed in hazardous locations classified as Class I, Division 2 or Class I Zone 2 under commonly used worldwide regulations. These regulations are: the National Electrical Code (United States); the Canadian Electrical Code, Part 1 (Canada); and combined practices of the International Electrotechnical Commission (IEC), the European Committee for Electrotechnical Standardization (CENELEC), and Standards Australia / Standards New Zealand (AS/NZS). Included is a list of source documents, definitions and nomenclature. Devices include terminal housings, heaters, surge protection, power factor correction capacitors, shaft grounding, and enclosures. Special marking requirements are also discussed.