WG 23-04 has published general guidelines for the design of outdoor AC substations (Publ.-69). Apart from some minor comments the scope was limited to air-insulated switchgear (AIS). Therefore all points which are specific for GIS for rated voltages of 72.5 kV and above or different from AIS are covered by this new application guide. Selection of most suitable site, area requirements, environmental factors and substation layout are described here.