The Court of Appeal has overturned a High Court decision and found that the ESB has no liability for extensive flood damage to parts of University College Cork's campus in 2009.
The High Court found more than two years ago that the ESB was 60% liable for the floods.
But the Court of Appeal found the damage arose from a natural event, ESB did not cause the flooding of UCC's buildings and it had no legal duty to avoid unnecessary flooding.
It found that the High Court had erred in holding that the ESB had a legal duty to provide more space in the reservoirs.
It also found the ESB was not negligent in respect of warnings.
It ruled that if the High Court judgment was allowed to stand it would represent a significant alteration in the existing law of negligence and nuisance.
This would be contrary to the ESB's mandate in respect of electricity generation and would not be consistent with reason and justice it found.
Liability for the costs of the action, which ran for more than 100 days in the High Court, will be decided later.