Selection of Ex-proof electrical equipment in hazardous locations
Selection of electrical equipment in hazardous locations shall be based on the classification of hazardous areas,combustible materials and combustible dust classification,the ignition temperature of flammable substances and flammable dust clouds,and the minimum ignition temperature of combustible dust layer,etc.
1.Basic principles of the selection of explosion-proof electrical equipment
1.1 Security and reliability:types,class or groups of equipments shall adapt to explosive environments.
1.2 Economical principle :the selection of equipment do not have high requirements,for the same grade of products,the prices,lifetime,reliability,energy consumption and operating costs,availability of spare parts and other factors shall be considered.
1.3 Adaptability to environment:Consider the ambient temperature,humidity,atmospheric pressure;enclosure protection rating as well as corrosion resistance ability and so on.
1.4 Maintainability:Under the same conditions,choose products with simple structure,light weight;also consider the operational requirements of the system when necessary.
1.5 Only choose Ga protection products for Zone 0,for equipments or high voltage equipments that ignition sources often formed inside enclosure shall not be used in zone 1,Exd/Exp equipment shall be used in Zone 1 when necessary.
2.Relationship between hazardous area classification and equipment protection degree
Table 1 - Equipment protection levels (EPLs) Where only Zones are assigne
| Zone | Equipment protection levels (EPLs) |
| 0 | “Ga” |
| 1 | “Ga” or “Gb” |
| 2 | “Ga”,“Gb” or “Gc” |
| 20 | “Da” |
| 21 | “Da” or “Db” |
| 22 | “Da”,“Db” or “Dc” |
Quoted from IEC60079-14:2013 Table 1
3.Relationship between equipment protection level (EPL) and explosion-proof structure of device
Table 2 - Default relationship between types of protection and EPLs
| EPL | Type of protection | Code | According to |
| “Ga” | Intrinsically safe | “ia” | IEC 60079-11 |
| Encapsulation | “ma” | IEC 60079-18 | |
| Two independent types of protection each meeting EPL | “Gb” | IEC 60079-26 | |
| Protection of equipment and transmission systems using optical radiation | “op is” | IEC 60079-28 | |
| Special protection | “sa” | IEC 60079-33 | |
| “Gb” | Flameproof enclosures | “d” | IEC 60079-1 |
| Increased safety | “e” | IEC 60079-7 | |
| Intrinsically safe | “ib” | IEC 60079-11 | |
| Encapsulation“m” | “m” | IEC 60079-18 | |
| Oil immersion | “o” | IEC 60079-6 |
| EPL | Type of protection | Code | According to |
| “Gb” | Pressurized enclosures | “p”,“px” “py”,“pxb” or “pyb” | IEC 60079-2 |
| “Gc” | Powder filling | “q” | IEC 60079-5 |
| Fieldbus intrinsically safe concept (FISCO) | IEC 60079-27 | ||
| Protection of equipment and transmission systems using optical radiation | “op is” | IEC 60079-28 | |
| “op sh” | |||
| “op pr” | |||
| Special protection | “sb” | IEC 60079-33 | |
| Intrinsically safe | “ic” | IEC 60079-11 | |
| Encapsulation | “mc” | IEC 60079-18 | |
| Non-sparking | “n” or “nA” | IEC 60079-15 | |
| Restricted breathing | “nR” | IEC 60079-15 | |
| Energy limitation | “nL” | IEC 60079-15 | |
| Sparking equipment | “nC” | IEC 60079-15 | |
| Pressurized enclosures | “pz”or“pzc” | IEC 60079-2 | |
| Protection of equipment and transmission systems using optical radiation | “op is” | IEC 60079-28 | |
| “op sh” | |||
| “op pr” | |||
| Special protection | “sc” | IEC 60079-33 | |
| “Da” | Encapsulation | “ma” | IEC 60079-18 |
| Protection by enclosure | “ta” | IEC 60079-31 | |
| Intrinsically safe | “ia” | IEC 60079-11 or | |
| IEC 61241-11 | |||
| Special protection | “sa” | IEC 60079-33 | |
| “Db” | Encapsulation | “mb” | IEC 60079-18 |
| Protection by enclosure | “tc” or “tD” | IEC 60079-31 | |
| IEC 61241-1 | |||
| Pressurized enclosures | “pD” | IEC 61241-4 | |
| Intrinsically safe | “ib” or “ibD” | IEC 60079-11 or IEC 61241-11 | |
| Special protection | “sb” | IEC 60079-33 | |
| “Dc” | Encapsulation | “mc” | IEC 60079-18 |
| Protection by enclosure | “tc” or “tD” | IEC 60079-31 | |
| IEC 61241-1 | |||
| Pressurized enclosures | “pD” | IEC 61241-4 | |
| Intrinsically safe | “ic” | IEC 60079-11 | |
| Special protection | “sc” | IEC 60079-33 |
New protection marking codes with identification of EPLs may be introduced in the future
Quoted from IEC60079-14:2013 Table 2
4.Selection of the class and group of explosion-proof equipment
The class and group of explosion-proof equipment in explosive atmosphere shall not be lower than that of the explosive gas mixture.Relationship between the classification of gas/vapor or dust and equipment level shall be in accordance with Table Relationship between gas/vapor or dust subdivision and equipment group.When an explosive mixture of two or more flammable substances formed,explosion-proof equipment shall be choosen based on the mixed explosive mixture levels and groups,if there is no evidence or cannot be test,equipments shall be choosen according to high level and group.For explosion-proof equipments that indicating applicable particular gas or vapor environment,if not identified,the equipment can’t be used in other gas atmosphere.Relationship between gas or vapor ignition temperature and temperature class of equipment of class II equipment shall be in accordance with below table.Device structure shall ensure that the equipment Ex performance will not be degraded under operating conditions.Relationship between classification of gases/vapors,dust and selection of equipment types.
Table 3 - Relationship between gas/vapour or dust subdivision and equipment group
| Location gas/vapour or dus subdivision | Permitted equipment group |
| IIA | II,IIA,IIB or IIC |
| IIB | II,IIB or IIC |
| IIC | II or IIC |
| IIIA | IIIA,IIIB or IIIC |
| IIIB | IIIB or IIIC |
| IIIC | IIIC |
Quoted from IEC60079-14:2013 Table 3
Table 4 - Relationship between gas and vapour ignition temperature and temperature class of equipment
| Temperature class required by the areaclassification | Ignition temperature of gas or vapour in C |
Allowable temperature classes of equipment |
| T1 | > 450 | T1 -T6 |
| T2 | > 300 | T2 -T6 |
| T3 | > 200 | T3 -T6 |
| T4 | > 135 | T4 -T6 |
| T5 | > 100 | T5 -T6 |
| T6 | > 855 | T6 |
Quoted from IEC60079-14:2013 Table 4
5.The special symbols or marks on the explosion-proof electrical equipment
The special symbols or mark on the explosion-proof electrical equipment shall be noted,if the explosion-proof certificate number with a suffix "U",it indicates that the device is with a component certificate,which can’t be used directly in the field,it must be used together with the main device after being certified as a whole;if with a suffix "X",it indicates that this equipment requires use under special conditions.
