The ESB is to investigate if interconnectors between Ireland, Northern Ireland and Scotland were responsible for the power failure which affected 200,000 homes and businesses.
The power cut began across the country at 10.10am today and lasted nearly two hours.
The ESB said some customers were only affected for a few minutes and the vast majority of customers had power back within one hour.
"An immediate investigation is being launched and while it is not possible to pre-empt the results, one focus of the enquiry is on the operation of interconnectors. Other factors will also be considered," said a spokesman.
The ESB has three interconnectors, powerlines which link one system to another, with Northern Ireland, and there is also the Moyle interconnector between Northern Ireland and Scotland.
They are designed to allow electricity to be traded between the countries and to ensure a greater security of power supply.
The ESB spokesman said that power failures for the company's 1.8 million customers had become much less frequent.
"This type of disruption, up to five or 10 years ago, would have happened relatively commonly. But obviously as a result of the major investment in the power system, we have managed to limit this. This kind of thing can happen on any power system."
He said the investigation would focus on putting measures in place to ensure there was no repeat of the problem.
The ESB is investing over €2.5 billion in the electricity transmission and distribution system.