The Difference Between Explosion-Proof Level BT1 and BT4

Both items are rated as IIB for explosion protection, differing only in their temperature classifications.

Temperature group of electrical equipment	Maximum allowable surface temperature of electrical equipment (℃)	Gas/vapor ignition temperature (℃)	Applicable device temperature levels
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

The designations T1 through T6 denote the maximum allowable surface temperatures for equipment under specific conditions, progressively decreasing. Lower temperatures signify higher safety.

Consequently, BT1 has a slightly lower explosion-proof rating compared to BT4.