Temperature Classification


Temperature classification takes into account the ignition temperature of the flammable gases present in the particular environment.

Ambient temperatures are of course considered in this appraisal; however circumstances which may increase this surface temperature must also be taken into account.

For example, an enclosure over a period of time, collects a layer of dust on its surfaces. This shall increase the units overall operating and surface temperatures, to a point where if it rises to a point nearing the flash or combustion point of surrounding gases, liquids or dusts, an explosive situation would occur.

For Group I classified electrical equipment, where coal dust can form a layer, the maximum surface temperature shall not exceed 150°C. If this layer can be avoided through sealing or protection from the ingress of dust, the internal surfaces must not exceed 450°C.

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.

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.

Therefore those items certified as being T6 can be used in T1, T2, T3, T4, T5 and T6 gases. Whereas a T2 certification only allows a piece of equipment to be used in T1 and T2 gases.

Temperature Class Table

Temperature Class T1 T2 T3 T4 T5 T6
Maximum surface temperature (ºC) <450 <300 <200 <135 <100 <85


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