• PollutionThe microenvironment det

• PollutionThe microenvironment determines the effect of pollution on the insulation. The macroenvironment, however, has to be taken into account when considering the microenvironment.Means may be provided to reduce pollution at the insulation under consideration by effective use of enclosures, encapsulation or hermetic sealing. Such means to reduce pollution may not be effective when the equipment is subjected to condensation or if in normal use, it generates pollutants itself.Small clearances can be bridged completely by solid particles, dust and water and therefore minimum clearances are specified where pollution may be present in the microenvironment.NOTE 1 Pollution will become conductive in the presence of humidity. Pollution caused by contaminated water, soot, metal or carbon dust is inherently conductive.NOTE 2 Conductive pollution by ionized gases and metallic depositions occur only in specific instances, for example in arc chambers of switchgear or controlgear and is not covered by IEC 60664-1.• Degrees of pollution in the microenvironmentFor the purpose of evaluating creepage distances, the following four degrees of pollution in the microenvironment are established:– pollution degree 1: no pollution or only dry, non-conductive pollution occurs. The pollution has no influence;– pollution degree 2: only non-conductive pollution occurs, except that occasionally a temporary conductivity caused by condensation is to be expected;– pollution degree 3: conductive pollution occurs or dry non-conductive pollution occurs that becomes conductive due to condensation that is to be expected;– pollution degree 4: the pollution generates persistent conductivity caused by conductive dust or by rain or snow.NOTE 3 Pollution degree 4 is not applicable to appliances.