The size selection of cables is not only to avoid the excessive heating and the danger of fire, but also to insure the service and the reliability of the concerned electric circuit. In the context of the dimension of the cables, some standards should be observed and necessary calculations should be done. With the requirement of the worldwide expansion application on Internet, the approach and the architecture of a complete Web-aided design platform are proposed for dimensioning the cables. The platform supports some calculation methods which are necessary for selecting the cables. Both XML documents and databases are used to interchange power system data and calculation results between Web servers and clients.