Surface Insulation Resistance (SIR), a measure of the electrical resistance of the surface of an insulator. Its units are ohms, but normally quoted as ‘ohms per square’, reflecting the fact that the resistance value measured between conductors will depend linearly on their separation and inversely on their width. SIR test means a test for the maintenance of a high SIR value under conditions of applied voltage, temperature and humidity, which is used to assess the suitability of flux materials and cleaning processes. Ionic residues lead to rapidly deteriorating values of SIR.
