According to national standards for electrical explosion protection, both BT4 and BT6 fall under Class IIB.
| Classification thermique des équipements électriques | Température maximale admissible à la surface des équipements électriques (°C) | Température d'inflammation des gaz/vapeurs (°C) | Classe de température applicable à l'équipement |
|---|---|---|---|
| T1 | 450 | >450 | T1~T6 |
| T2 | 300 | >300 | T2~T6 |
| T3 | 200 | >200 | T3~T6 |
| T4 | 135 | >135 | T4~T6 |
| T5 | 100 | >100 | T5~T6 |
| T6 | 85 | >85 | T6 |
However, the ‘T’ classification pertains to the temperature rating of explosion-proof electrical devices. Devices classified as T6 must maintain a surface temperature no higher than 85°C, T5 must not exceed 100°C, and T4 must not surpass 135°C.
The lower a device’s maximum surface temperature, the less likely it is to ignite atmospheric gases, thereby enhancing safety. Consequently, the explosion-proof rating of BT6 exceeds that of BT4.
