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Delta, in conjunction with Helicopters Otago, is conducting a close-quarters survey of the 33kV distribution power lines throughout coastal and Central Otago, including Berwick to Port Chalmers, and Millers Flat to Queenstown and Wanaka.
Helicopters Otago managing director Graeme Gale wanted to make people aware of the work so there were "no surprises". A mailbox drop had been done to inform owners of stock and horses.
The work began on Tuesday and it was hoped to have it completed by Christmas, although it was weather-dependent.
Brian Mathiesen (CRCT), from TransNet New Zealand, said the work was to ensure security of the three circuits, by preventing outages.
Mr Mathiesen was in the helicopter, operating a corona camera which identified any insulators that needed replacement and that information was then relayed to Delta.
Humidity had to be over 60% for the German-designed camera — which was worth "$70,000-odd" — to work, he said.
It was a slow process. There were about 600 poles on the circuit and three insulators on each pole.