| numeral characterizing the expected pollution of the micro-environment
NOTE – For the purpose of evaluating creepage distances and clearances, the following four pollution degrees in the microenvironment are established in 2.5.1 of IEC 60664-1:1992.
a) pollution degree 1: No pollution or only dry, non-conductive pollution occurs. The pollution has no influence.
b) pollution degree 2: Only non-conductive pollution occurs except that occasionally a temporary conductivity caused by condensation is to be expected.
c) pollution degree 3: Conductive pollution occurs, or dry, non-conductive pollution occurs which becomes conductive due to condensation is to be expected
d) pollution degree 4: The pollution generates persistent conductivity caused by conductive dust or by rain or snow.