IEC Classifications
| Temperature Classes (for gas atmosphere) |
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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”.
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Ignition temperature of medium relative to limit temperature
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Temperature class
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Maximum surface temperature of electrical equipment including 40°C ambient temperature |
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[°C]
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[°C]
|
[°C]
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| over 450 |
T1
|
450
|
842
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| from 300 to 450 |
T2
|
300
|
572
|
| from 200 to 300 |
T3
|
200
|
392
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| from 135 to 200 |
T4
|
135
|
275
|
| from 100 to 135 |
T5
|
100
|
212
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| from 85 to 100 |
T6
|
85
|
185
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| 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 |
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Zone 0
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Zone 20
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explosive atmosphere is ALWAYS PRESENT.
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Zone 1
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Zone 21
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explosive atmosphere is
PROBABLE
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Zone 2
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Zone 22
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explosive atmosphere is NOT LIKELY
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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. |
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