Reliance Technology and Service installed Pressurized System in Gas Insulated Switchgear (GIS) Sub-stations (nos. 4 and 5). This was at PTT Chem (PTTCH) site in Map Ta Phut, Rayong during early 2010. Our scope included the design, calculation, equipments supply (blower, duct work, shutter, damper controller and control panels), installation and commissioning of the system. Pressurize control was for positive pressure of 10 mmH2O.