Selecting porcelain/glass insulators for three-phase AC systems up to 525 kV phase-to-phase using IEC/TR 60815 has been based on service experience and laboratory tests under polluted conditions. But many utilities have simply standardized on one or more of the values of minimum Specific Creepage Distance for Light, Medium, Heavy and Very Heavy polluted environments. The focus of this presentation is to show how the old technical recommendation, i.e., IEC/TR 60815 and the new technical specification i.e. IEC/TS 60815 are being used by a large power utility when selecting outdoor insulators for application in polluted areas. Emphasis is placed on approaches based on measuring ESDD as well as using data collected from directional dust deposit gauges.