Evaluation of Maximum Rotor Temperatures in Tefc Inverter-Fed Motors

When installing an induction motor in a Class I, Division 2 hazardous (classified) area, it is H Y in the interest of both the user and the manufacturer to insure that the installed motor will not become a source of ignition of flammable gases or vapors in the classified area. Article 501 of the National Electrical Code, NFPA 70, contains regulations governing such motor installations [1]. Article 501-8(b) allows the use of explosion-proof motors or “open or nonexplosion-proof enclosed motors, such as squirrel-cage induction motors without brushes, switching mechanisms, or similar arc-producing devices….” Fine Print Note No. 1, which follows Article 501-8(b), then instructs the reader that “It is important to consider the temperature of internal and external surfaces that may be exposed to the flammable atmosphere.”