As constituted in 1923 the Joint Authority transferred all its rights to distribution of electricity in the area to the North Wales Power Company.
Both the joint authority and the power company were abolished in 1948 upon the nationalisation of the British electricity supply industry.
[1] The Power company developed several hydro-power stations and extended transmission lines to towns and industrial areas.
At Cwm Dwli water was drawn from Lake Llydaw and flowed through tunnels and steel pipes to the power station in the Gwynant valley.
The district included Anglesey, Caernarvonshire, Denbighshire, Flintshire, Merionethshire, Montgomeryshire, and parts of Cheshire, Shropshire, and Cardegoneshire.
[2] This was used to construct several major projects: to build the Maentwrog power station with an initial capacity of 16,000 horsepower (12 MW); to increase the catchment area of the Cwm Dyli power station; to extend the transmission system to Crewe, to industrial districts, and to coastal towns.