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Temperature classes for gas atmospheres

The electrical apparatus is classified into 6 classes according to the maximum surface temperatures. The maximum surface temperature is the highest temperature which is attained in service under the conditions described in the standards, by any part of the electrical apparatus, which, could ignite the surrounding atmosphere.

For electric motors this is:

  • the temperature of the outside surface of the enclosure for “d” and “p”
    protection modes;
  • the temperature of any internal or external point for type of protection“e” or “n”.

Ignition temperature
of medium relative
to limit temperature
Maximum surface temperature
of electrical equipment including
40°C ambient temperature
over 450T1450842
from 300 to 450T2300572
from 200 to 300T3200392
from 135 to 200T4135275
from 100 to 135T5100212
from 85 to 100T685185