IEC Classifications
Temperature Classes (for gas atmosphere)

The electrical apparatus are classified into 6 classes according to their maximum surface temperature. The maximum surface temperature is the highest temperature which is attained in service under the conditions described in the Standards, by any part of an electrical apparatus, which is able to produce an ignition of the surrounding atmosphere.
For motors, it concerns:

  • the temperature of the external surface for types of protection “d” or “p”
  • the temperature of any internal or external point for type of protection “e” or “n”.
Ignition temperature of medium relative to limit temperature
Temperature class
Maximum surface temperature of electrical equipment including 40°C ambient temperature
[°C]
 
[°C]
[°C]
over 450
T1
450
842
from 300 to 450
T2
300
572
from 200 to 300
T3
200
392
from 135 to 200
T4
135
275
from 100 to 135
T5
100
212
from 85 to 100
T6
85
185
Dangerous areas classified by zones
Usage in areas with presence of GAS Usage in areas with the presence of DUST Hazardous level of the operational ZONE
Zone 0
Zone 20

explosive atmosphere is ALWAYS PRESENT.

Zone 1
Zone 21
explosive atmosphere is
PROBABLE
Zone 2
Zone 22
explosive atmosphere is NOT LIKELY
 

IEC Combustion

NEMA-UL Classifications
NEC Temperature Codes
T Code with Maximum Temperature
T1 450°C (842°F)
T2 300°C (572°F)
T2A 280°C (536°F)
T2B 260°C (500°F)
T2C 230°C (446°F)
T2D 215°C (419°F)
T3 200°C (392°F)
T3A 180°C (356°F)
T3B 165°C (329°F)
T3C 160°C (320°F)
Motor Classifications for Hazardous Locations*
Classifications Characteristics
Class I, Group A: Atmospheres containing
acetylene.
Class I, Group B: Atmospheres containing
hydrogen or gases or vapors of equivalent hazards
such as manufactured gas.
Class I, Group C:
.
Atmospheres containing ethyl
ether vapors, ethylene or cyclopropane.
Class I, Group D: Atmospheres containing gasoline,
hexane, naphtha, benzene, butane, alcohol, acetone,
benzyl, lacquer solvent vapors, or natural gas.
Class II, Group E: Atmospheres containing metal
dust, including aluminum, magnesium, and their
commercial alloys, and other metals of similarly
hazardous characteristics.
Class II, Group F: Atmospheres containing carbon
black, coal or coke dust.
Class II, Group G: Atmospheres containing flour,
starch, or grain dust
*Each of these classes is further divided into Division I, continously hazardous, and Division II, occasionaly but not normally hazardous.