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Aurora says the promotion could be causing disruption to customers in the student quarter, but Electric Kiwi says issues around housing stock and infrastructure investment could be to blame.
Electric Kiwi offers one daily off-peak hour of free power.
The Otago Daily Times spoke to occupants of three flats in Harbour Tce and Dundas St in North Dunedin yesterday and all used Electric Kiwi and opted for 9pm to 10pm as their free hour.
Dundas St resident Isabella Peck (19) said her six-person flat had cuts during this period three nights in the past week.
''It's a pain in the butt.''
They made the most of the free hour, she said.
''We'll have six heaters on, three or four electric blankets, drier, washing machine.''
Their house was not insulated and windows were single-glazed, so was difficult to heat, she said.
Harbour Tce resident Kacee Grant said her four-person flat had four cuts in the last week.
''We don't use a lot. We literally only have a drier on.''
Each time a Delta worker would be sent to fix the problem, and power could take hours to come back on, she said.
''We're all just at our wits' end.''
The problems only started in the past week, she said.
Dundas St resident Travis Egerton said his five-person flat had two cuts in the past week.
The flat used ''everything'' during that hour to save money, he said.
Electric Kiwi chief executive Luke Blincoe said he was disappointed to hear about the issues, but it was ultimately related to ''physical infrastructure'' in the form of networks and housing.
''This product may well be increasing usage during the evening compared to historical trends, but from our perspective if enabling people to heat their homes appropriately results in power outages then issues around housing stock and network investment are far more urgent than we might realise.''
The company had not noticed similar problems in other parts of the city or in other areas, he said.
An Aurora spokesman said it recently received an increased number of repeat calls to replace blown service fuses caused by spikes in consumption.
The hour of free power promotion could be contributing, he said.
While it supported retailers' innovate service offerings, it needed to work with them to ensure promotions did not result in disruption to customers, increased operating costs or oversized infrastructure to meet short-term peak demands, he said.
Its engineering group was working on short and long-term solutions.