Which Explosion-Proof Level Is Higher, BT4 or BT6

According to national standards for electrical explosion protection, both BT4 and BT6 fall under Class IIB.

Temperature Classification for Electrical Equipment	Maximum Permissible Surface Temperature of Electrical Equipment (°C)	Gas/Vapor Ignition Temperature (°C)	Applicable Equipment Temperature Class
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.