Explosion-proof limit switch

2. Applicable to IIA, IIB, IIC explosive gas environment;

3. Applicable to flammable dust environment in Zone 20, Zone 21, Zone 22;

4. Applicable to the environment where the temperature group is T1—T6.

Scope of application

1.1 Classification of hazardous areas of explosive gas environment 
　　Different countries and regions divide explosion hazardous areas according to their respective standards. China divides the explosive gas environment into O zone, zone 1 and zone 2 according to the frequency and duration of the explosive gas mixture. (consistent with the IEC International Electrotechnical Commission) 
　　Zone 0: An environment in which explosive gas mixtures are continuously or permanently present. 
　　Zone 1: An environment in which an explosive gas mixture may be present during normal operation. 
　　Zone 2: The environment in which an explosive gas mixture is unlikely to occur during normal operation or the environment of an explosive gas mixture that is present only for a short period of time. 
　　Zone 0 generally exists only in sealed containers, storage tanks and other internal gas spaces. In the actual design process, Zone 1 is also rare, and most of them belong to Zone 2. 
　　1.2 Explosion-proof electrical equipment is divided into two categories: 
　　Class I coal mine underground electrical equipment 
　　Class II electrical equipment used in addition to mines 
　　Class 1.3 Class II electrical equipment, according to its maximum test safety clearance or minimum ignition current ratio for explosive gas mixtures, Divided into IIA, IIB, IIC three categories; and according to its highest surface temperature is divided into six groups of T1-T6. 
　　1.4 Explosive gas mixtures are grouped according to ignition temperature, see Table 1. 
　　1.5 Explosive gas mixture, classified according to its maximum test safety clearance (MESG) or minimum ignition current ratio (MICR), see Table 2. 
　　Table 1 
　　group 
　　Ignition temperature t (°C) 
　　T1 
　　450<t 
　　T2 
　　300<t≤450 
　　T3 
　　200<t≤300 
　　T4 
　　135<t≤200 
　　T5
　　100 <t≤135 
　　T6 
　　85 <T ≦ 100 
　　Table 2 
　　Type 
　　maximum experimental safe gap (MESG) (mm) 
　　the minimum ignition current ratio 
　　IIA 
　　≥0.9 
　　> 0.8 
　　IIB 
　　0.5 <MESG <0.9 
　　0.45≤MICR≤0.8 
　　òC 
　　≤0.5 
　　<0.45 
　　Properties : The ratio of the minimum ignition current of a gas, vapor explosive mixture to the minimum ignition current of an explosive mixture of methane under specified test conditions. China stipulates that gas and vapor hazardous substances are classified into Class IIA, Class IIB and Class IIC according to the minimum ignition current ratio. The minimum ignition current ratio is ≤1.0, >0.8 is IIA; ≤0.8, >0.45 is IIB; ≤0.45 is IIC. For example, ethane, ethylene, and acetylene are Class IIA, Class IIB, and Class IIC hazardous materials, respectively.