Equipment installed in Class III locations shall be able to function at full rating without developing surface temperatures high enough to cause excessive dehydration or gradual carbonization of accumulated fibers or flyings. As noted previously, organic material that is carbonized or excessively dry is highly susceptible to spontaneous ignition. The maximum surface temperatures under operating conditions shall not exceed 165°C (329°F) 165°C (329°F)
This is equivalent to a T3B temperature code marking as given in Table 500.8(C). for equipment that is not subject to overloading, and 120°C (248°F) 120°C (248°F)
This is equivalent to a T4A temperature code marking as given in Table 500.8(C). for equipment (such as motors or power transformers) that may be overloaded.

NOTE: This is an unformatted excerpt from our online fire protection training library.