4 • Application in Explosive Environments
Classification meeting CENELEC and IEC
Ex-1.3.4 Temperature classes
The maximum surface temperature for electrical components of explosion protection group I is 150 °C (danger due to coal dust deposits) or 450 °C (if there is no danger of coal dust deposit).
In line with the maximum surface temperature for all ignition protection types, the electrical components are subdivided into temperature classes, as far as electrical components of explosion protection group II are concerned. Here the temperatures refer to a surrounding temperature of 40 °C for operation and testing of the electrical components. The lowest ignition temperature of the existing explosive atmosphere must be higher than the maximum surface temperature.
Temperature classes | Maximum surface | Ignition temperature | |
| temperature | of the combustible materials | |
T1 | 450 °C | > 450 | °C |
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T2 | 300 °C | > 300 | °C ≤ 450 °C |
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T3 | 200 °C | > 200 | °C ≤ 300 °C |
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T4 | 135 °C | > 135 | °C ≤ 200 °C |
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T5 | 100 °C | >100 °C ≤ 135 °C | |
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T6 | 85°C | > 85 | °C ≤ 100 °C |
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The following table represents the division and attribution of the materials to the temperature classes and material groups in percent:
Temperature classes |
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T1 | T2 | T3 | T4 |
| T5 | T6 | Total* |
26.6 % | 42.8 % | 25.5 % |
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| 94.9 % |
| 4.9 % |
| 0 % | 0.2 % | 432 |
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Explosion group |
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IIA | IIB | IIC |
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| Total* |
80.2 % | 18.1 % | 0.7 % |
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| 436 |
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| * Number of classified materials |
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Ex-1.3.5 Types of ignition protection
Ignition protection defines the special measures to be taken for electrical components in order to prevent the ignition of surrounding explosive atmospheres. For this reason a differentiation is made between the following types of ignition protection:
