Thieves in Waikato are stealing power cables in rural areas up to 25 times a week.
Acting Detective Senior Sergeant Neville Ross, of Hamilton police, said they had arrested six people, and more arrests were likely.
The $10,000 value of the stolen earth cables was well below the amount it cost electricity companies to replace them, Mr Ross said.
He urged people to check whether workers on or near power poles or wires had an electricity company vehicle with them.
