Former Delta Energy worker Richard Healey says he has evidence from inside Aurora showing five of the city's eight underground high-voltage cables are failing or damaged.
Aurora Energy chairman Steve Thompson rejected those claims, saying Mr Healey was provoking unnecessary alarm.
Mr Healey has written to the Commerce Commission detailing his concerns with information passed on to him by people still working within the lines company, which he says shows he is telling the truth.
High-voltage cables supplying the Smith St, Willowbank and Neville St substations were all out of service because of gas leaks, Mr Healey said.
There were also other issues at the Green Island and North City substations, which all meant Dunedin's power network was very vulnerable, he said.
Mr Thompson rejected all of Mr Healey's claims and said the public could be confident in Aurora Energy's sub-transmission network.
``The accurate situation is that all Dunedin zone substations are in service and none of the cables that supply them have failed.''
Individual cables were occasionally taken out of service for repairs or routine maintenance, he said.
``As is prudent, Aurora Energy is progressively upgrading its older, gas-insulated sub-transmission cables in Dunedin to modern cables with solid insulation.''
An upgrade of the Andersons Bay cable was completed in 2013 and an upgrade of the Neville St cable was under way and scheduled for completion by August 2018.
Over the next five years there would be cable upgrades for the Smith St, Willowbank and Kaikorai Valley substations, he said.
A Commerce Commission spokeswoman said its investigation into Aurora for breaching limits on the duration and frequency of system outages or interruptions on its network in the 2015-16 financial year was ongoing.
It was also looking into a quality standard breach by the lines company in the 2016-17 financial year.
