Temperature Classes For Hazardous Area


The ignition temperature of a flammable gasquid is the lowest temperature of a hot surface at which ignition of the gas/air or vapour/air mixture takes place. The maximum surface temperature of the equipment must therefore be lower than the ignition temperature of the ambient atmosphere.
In respect to Group II electrical equipment, temperatures are classified as per the following table.

In respect to Group III, the surface temperature is given in considering the thickness of the dust layer, Practice A or Practice B, in marking equipment with its maximum T* rating. ie: T80°C.

For example, a T6 certification for euipment which has a maximum permissible surface temperature of 85°C can be used in T5, T4, T3, T2 and T1 environments.

Similarly, a T4 certification for equipment which has a maximum oermissible surface temperature of 135°C can NOT be used in a T5 or T6 environment, but can be used in T3, T2 and T1 environments.

Temperature class T1 to T6 are used for all protection techniques and correspond to the electrical devices maximum operational temperature.
The better the equipment, the lower the rated surface temperature. In other words, a rating of T4 is better than T2.


Temperature Classes Table:

 Hazards which will not ignite at temperature below:



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