A complete intrinsically safe (“i”) Ex mark usually follows the following structure, which is elaborated in detail by STS:
Ex ia/ib/ic [Intrinsically Safe Ex Rating] IIC/IIB/IIA T1~T6 [Equipment Protection Level]
1. Ex Mark
Ex: It is an internationally universal Ex mark, indicating that the equipment is an explosion-proof electrical device.
2. Ex Type (ia/ib/ic)
ia, ib, ic: These are the protection levels of the intrinsically safe Ex type, representing the safety degree of the equipment.
- ia Level: The highest safety level. It cannot ignite explosive gases under normal operation + 2 counted faults + non-technical faults under the most unfavorable conditions. Applicable to Zone 0, Zone 1, and Zone 2.
- ib Level: A high safety level. It cannot ignite explosive gases under normal operation + 1 counted fault + non-technical faults under the most unfavorable conditions. Applicable to Zone 1 and Zone 2.
- ic Level: It cannot ignite explosive gases under normal operation. Only applicable to Zone 2.
3. Explosive Gas Atmosphere Group (Gas Group)
It indicates the type of explosive gas atmosphere applicable to the equipment, classified according to the Minimum Ignition Current (MIC) of gases.
- IIC: Representative gases include hydrogen (H?) and acetylene (C?H?). It is the group with the highest requirements, marking that the equipment has the strongest Ex capability. IIC equipment can be safely used in IIB and IIA environments.
- IIB: The representative gas is ethylene (C?H?). IIB equipment can be safely used in IIA environments.
- IIA: Representative gases include propane (C?H?) and acetone. It is the group with the lowest requirements.
Simply put: IIC > IIB > IIA. The later the alphanumeric suffix (e.g., C), the stronger the Ex capability and the wider the applicable gas range.
4. Temperature Class
It indicates that the maximum surface temperature of the equipment's surface or internal components will not exceed this value under normal operating conditions.
- T1 ≤ 450°C
- T2 ≤ 300°C
- T3 ≤ 200°C
- T4 ≤ 135°C
- T5 ≤ 100°C
- T6 ≤ 85°C
5. Equipment Protection Level (EPL)
It is a classification based on the probability of the equipment becoming an ignition source, directly corresponding to hazardous areas.
- Ga (Very High Level of Protection): Applicable to Zone 0, Zone 1, and Zone 2. The IS ia level usually corresponds to Ga.
- Gb (High Level of Protection): Applicable to Zone 1 and Zone 2. The IS ib level usually corresponds to Gb.
- Gc (General Level of Protection): Only applicable to Zone 2. The IS ic level usually corresponds to Gc.
Note: Ga/Gb/Gc is a newer expression that is gradually becoming popular. It more intuitively associates equipment with hazardous areas.
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