A report from fire investigators says Unison power lines were responsible for the cause of the wildfires on Waimarama Rd in 2017.
The report, released under the Official Information Act, found that clashing of wires caused "super-heated material igniting the vegetation below".
Unison disputes the finding, and says it is still in discussion with Fire and Emergency NZ over its attempt to reclaim the costs of fighting the fire, put at more than $627,000.
Crews were brought in from across New Zealand to fight the wild fire. which tore through 164 hectares of land which included farm and forestry - destroying one house and causing serious damage others.
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Investigators said the fire started in an area where Unison crews had been working. They found marks on power lines that showed signs of arching or clashing.
Pine plantations turned to ashes and fences and other farm infrastructure were also destroyed.
More than 100 cars and two bus-loads of children were escorted out of the Waimarama area and homes were evacuated, with a welfare centre set up at Havelock North Function Centre.
Unison relationship manager Danny Gough said he had no indication of when a resolution would be made with FENZ.
Gough said he was not in the position to comment further, should FENZ file legal proceedings.