<P> The rapid industrialization in the 20th century made electrical transmission lines and grids a critical part of the economic infrastructure in most industrialized nations . Interconnection of local generation plants and small distribution networks was greatly spurred by the requirements of World War I, where large electrical generating plants were built by governments to provide power to munitions factories; later these plants were connected to supply civil load through long - distance transmission . </P> <P> Small municipal electrical utilities did not necessarily desire to reduce the cost of each unit of electricity sold; to some extent, especially during the period 1880--1890, electrical lighting was considered a luxury product and electric power was not substituted for steam power . Engineers such as Samuel Insull in the United States and Sebastian Z . De Ferranti in the United Kingdom were instrumental in overcoming technical, economic, regulatory and political difficulties in development of long - distance electric power transmission . By introduction of electric power transmission networks, in the city of London the cost of a kilowatt - hour was reduced to one - third in a ten - year period . </P> <P> In 1926 electrical networks in the United Kingdom began to be interconnected in the National Grid, initially operating at 132 kV . </P>

When was electricity first commonly used in homes