The object of the paper is to indicate that the changing-over of existing low-tension networks from direct current to alternating current can be carried out in a satisfactory and advantageous manner from an engineering as well as from an economic standpoint.The problems arising in dealing with small townships, and with suburban and residential areas, are quite different from those which arise in industrial and city areas. The paper has consequently been divided into three parts, Part 1 dealing with suburban and residential areas, Part 2 with industrial and city areas, and Part 3 with the general aspect of changing over.As a result of investigations, the authors are of the opinion that, irrespective of loading conditions, residential and suburban areas should be changed over to a.c. supply at the earliest possible opportunity, but that in industrial and city areas the rate of change-over should depend upon the growth of the d.c. load and the condition of the d.c. converting plant. In all areas, however, the “standard” 3-phase 4-wire a.c. system should ultimately be adopted.