Enclosures for standard Stearns disc brakes are designed to prevent accidental contact with the internal mechanism while keeping contaminants from the operating parts. Many installations, however, require additional protection due to the presence of explosive gases or ignitable dusts in the atmosphere. Hazardous locations are defined in the National Electrical Code (NEC) and designated by Class, Division and Group. For a better understanding of hazardous locations, or for definitions of hazardous location terminology, please refer to: http://www.ul.com/global/eng/pages/offerings/services/hazardouslocations/
Class I – Locations where the atmosphere may contain flammable gases or vapors in explosive or ignitable concentrations. An electric disc brake for Class I locations must be built in such a manner that any ignition of gases or vapors within the brake will not result in rupture of the enclosure or allow a flame or spark to travel from within the brake to the surrounding hazardous atmosphere.
Class II – Locations with combustible dust in suspension in the atmosphere. An electric disc brake for Class II locations must be enclosed in a manner which precludes entry of ignitable dusts or exit of any arcs, sparks, or hot gases which may cause ignition of dusts suspended in the surrounding atmosphere or accumulated on the enclosure. The exterior surface temperature of the brake enclosure must be limited so that it can function at its maximum-rated duty cycle without causing dehydration or carbonization of dust that accumulates on the enclosure.
Divisions – Each hazardous-location Class is also divided into two Divisions, 1 and 2. Division 1 is a normally hazardous location. Division 2 is normally not hazardous. Division 1 brakes can be used in both types of locations. Division 2 can be used in Division 2 environments ONLY.
Groups – Class I gases and vapors are listed in four Groups A, B, C and D, based on specific properties such as maximum explosion pressure and ignition temperature. Class II airborne dusts are listed in three Groups: E, F, and G. The dust properties considered include thermal and electrical conductivity and ignition temperature.