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| | | Basics of Explosion Protection Temperature Classes; Explosion Groups | | |
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| | | Temperature Classes | | |
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| | | Ignition temperature is the lowest temperature of a surface at which an explosive atmosphere ignites on it. Flammable vapours and gases can be classified into temperature classes according to their ignition temperature. | | The maximum surface temperature of a piece of equipment must always be lower than the ignition temperature of the gas-air mixture or vapour-air mixture in which it is placed. | | |
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| | | Temperature Classes to IEC | | |
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| | | | | | | | | | | | Temperature class IEC / EN | Maximum permissible surface | Ignition temperatures of | Temperature class NEC 500-3 | | | | NEC 505-10 | temperature of the equipment | flammable substances | CEC 18-052 | | | | | [°C] | [°C] | | | | | T1 | 450 | >450 | T1 | | | | T2 | 300 | > 300 < 450 | T2 | | | | | 280 | > 280 < 300 | T2A | | | | | 260 | > 260 < 280 | T2B | | | | | 230 | > 230 < 260 | T2C | | | | | 215 | >215<230 | T2D | | | | T3 | 200 | > 200 < 300 | T3 | | | | | 180 | >180<200 | T3A | | | | | 165 | >165 <180 | T3B | | | | | 160 | >160 <165 | T3C | | | | T4 | 135 | >135<200 | T4 | | | | | 120 | >120 <135 | T4A | | | | T5 | 100 | >100 <135 | T5 | | | | T6 | 85 | >85< 100 | T6 | | | | | | | | | | | |
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| | | Explosion Groups Explosion protected electrical equipment is divided into 2 groups: Group I Electrical equipment for mining Group II Electrical equipment for all other hazardous areas | | |
| | | Electrical equipment of group II os further subdivided in groups IIA, MB and IIC, depending on the danger level of the gas or vapour atmosphere in which they are operated. Equipment of group IIC is suitable for use in the most dangerous atmospheres. | | |
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| | | Examples of the Classification of Gases and Vapours into Explosion Groups and Temperature Classes | | |
| | | | | | | | | | | | | | | | T1 | T2 | T3 | T4 | T5 | T6 | | | | 1 | Methane | | | | | | | | | IIA | Acetone Ethane Ethyl acetate Ammonia Benzene (pure) Acetic acid Carbon monixide Methane Methanol Propane Toluene | Ethyl alcohol i-amyl acetate n-butane n-butyl alcohol | | Acetaldehyde Ethyl ether | | | | | | MB | Town gas (coal gas) | Ethylene | | | | | | | | IIC | Hydrogen | Acetylene | | | | Carbon disulphide | | | | | | | | | | | | | | |
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| | | There is no classification of dust material into temperature classes or explosion groups. This means that the respective values are to be taken into account. The minimum ignition energy Emin (of a gas-air mixture) is the energy of an electrical spark that is capable of igniting the most critical (highest ignition performance) mixture under defined test conditions. Ignition temperature Tgn (of a gas-air mixture) is the lowest temperature of a hot wall surface at which the mixture is ignited after short-term contact. The glow temperature Tgiow (of a dust layer) is the lowest temperature of a hot surface on which ignition occurs in a 5 mm thick layer of dust. | | The maximum surface temperature of the equipment must be compared with the ignition temperature and the glow temperature while also taking into account the safety factor: • temperature limiting regarding dust clouds: I max — 2/3 I ign • temperature limiting regarding dust layers: Tmax = Tglow " 75 K (5 mm dust layer) The lower of the two values represents the maximum permissible surface temperature of the equipment. | | |
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| | | General Catalogue 13.02.2006 | | |
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