A power pylon in New Zealand collapsed and knocked out electricity to thousands after workers removed too many bolts, the country's transmission provider said on Monday.
The pylon, north of Auckland, fell on June 20, cutting power to about 100,000 properties in the Northland region of northern New Zealand. Full power was only restored on Sunday.
Transpower chief executive Alison Andrew said a crew from Omexom was undertaking routine maintenance on the base plates, which secure the tower to the ground, when the pylon fell.
"All the nuts securing the tower to the base plate on three legs have been removed which has caused the tower to lift off the base plate and fall," she said in a statement.
"It is unprecedented and inconceivable that so many nuts were removed at once."
A full investigation had been launched, she said.
"While we are very grateful that no one was hurt when the tower fell, the failure to follow procedure resulted in a significant power outage that had a real impact on the people of Northland," she said.
"We are committed to learning from this event and implementing any additional controls that may be identified."
Omexom managing director Mornez Green said the incident was unprecedented.
The workers involved had been stood down pending the investigation, he said.
"I can assure you we will be open and transparent in the investigation."