The Electricity Trust of South Australia was established  following proclamation of the Electricity Trust of South Australia Act  No. 3 of 1945. The Trust was empowered by part III of this Act to carry  out the functions of the former Adelaide Electric Supply Company, whose  assets became vested in the Trust. The functions of the Trust included  extending the supply of electric energy to suburban and country  consumers, construct power stations and facilities, investigate fuel  sources and review pricing structures for the supply of electricity.

On the 28 August 1945 a Royal Commission appointed by the South Australian Government to enquire into the supply of electricity by the Adelaide Electric Supply Company Limited reported that in its opinion, legislation to acquire the Company's assets and liabilities was desirable in the public interest. An Act to give effect to the Commission's recommendation was proclaimed on the 30 August 1946 and the Electricity Trust of South Australia came into being on 1st September 1946.

Prior to 1946, electricity production in South Australia can be traced to the formation in 1895 of the South Australian Electric Light and Motive Power Co Ltd, although numerous small generators had been operating prior to this date. In 1897 an Act of Parliament gave this company a franchise over power supply to Port Adelaide and the City of Adelaide as well as all corporate towns. The Act also provided for certain public control over its actions. After some changes of ownership the Adelaide Electric Supply Co, which was to operate the enterprise for the next 40 years, acquired the South Australian interests of the company including the franchise in 1904.
The first power station situated at Port Adelaide came into operation in 1899.

The trademark of electricity transmission in South Australia, the steel and concrete "Stobie pole", was developed in 1925.

In 1943 an inquiry was conducted into the general need for expansion of power supplies and in particular on a possible site for a new power station. Following this inquiry the South Australian Electricity Commission was established as a permanent investigating body. This process of inquiry into the activities of the Adelaide Electric Supply Co, culminated in 1944 with the appointment of a royal commission which eventually led to the establishment of the Electricity Trust of South Australia.

During the 1950's the Electricity Trust acquired and developed installations at Port Lincoln and Mount Gambier to supplement existing power stations situated at Port Augusta, (since 1954) and the "A" section of the Osborne power station. An oil-fired power station at Torrens Island was in operation by 1967.

By 1964, apart from ETSA, electricity supply in South Australia was also in the hands of some Local Government Bodies and various companies or individuals operating under Local Government franchises. ETSA, however supplied either directly or indirectly about 95% of the State's electricity requirements.

The Electricity Reticulation Advisory Committee was formed by 1979 to advise the trust on matters relating to the appearance and environmental effects of powerlines including the provision of advice on whether the cost of under-grounding is justified in particular situations. Apart from the Local Government Act 1934-1949 (which lays down the rights and responsibilities of Local Government Authorities in the establishment and operation of electricity trading undertakings) the principal acts governing electricity supply in South Australia are those under which ETSA operates. Namely:

- The South Australian Electric Light and Motive Power Company's 
   Act, 1897
- The Adelaide Electric Supply Company's Act, 1897-1931
- The Electricity Act, 1943
- Electricity Trust of South Australia Act, 1946
- Electricity Supplies (Country Areas) Act, 1950
- Electricity (Country Areas) Subsidy Act, 1962-1965
- Electrical Articles and Materials Act, 1939-1940
- Electrical Articles and Materials Act, 1940-1967
- Electrical Workers and Contractors Licensing Act, 1965-1978 


Sources

South Australian Year Book, 1966
Statistics of the Electric Supply Industry in Australia, 1964-1965 Electricity Trust of South Australia Annual Reports, 1957, 1971,
 1975, 1979
Historical agency address
1946-1952: Victoria Square, Adelaide
1952-1957: Kelvin Building, North Terrace, Adelaide (showroom
           premises) 
1957-1964: Cnr Rundle & Pulteney Streets, Adelaide (showroom
           premises) 
1964-    : 220 Greenhill Road, Eastwood SA (subject to further
           research)
Legislation administered
Creation: Electricity Trust of South Australia Act No.3 of 1946