An investigation into alleged code of conduct breaches by two major power companies in the wholesale market has found they did not break the rules.
The inquiry into Meridian and Contact's actions stemmed from a complaint of an undesirable trading situation by a group of electricity retailers.
In a draft decision in March, the Electricity Authority upheld the complaint finding the companies spilled excess water from South Island hydro dams causing a spike in wholesale prices which it estimated cost users about $80 million.
The authority ran a separate investigation into an alleged breach of the high standard of conduct set out in the industry code, but found they were protected by a safe harbour provision in the same code.
Electricity Authority chief executive James Stevenson-Wallace said: "The investigator concluded Meridian and Contact did not breach the high standard of trading conduct because available capacity was offered, offers were made and revised in a timely manner, and one of the set of conditions of the safe harbour rule was met".
"Specifically, both generators demonstrated consistent offers in periods where they were pivotal with offers in periods where they were not," Stevenson-Wallace said.
The code was designed to prevent individual power generators taking advantage of a lack of competition at times when they are relied on to make up the supply in the system.
The rules were being reviewed to address concerns that the safe harbour provisions were hard to apply in practice and that they could shelter behaviour which doesn't meet the standard.
The authority said it had consulted on the proposed rule changes and was aiming to have a final decision on new measures in June 2021.