Transpower chief executive Alison Andrew has confirmed maintenance crews removed all the nuts at the bottom of three legs of the power pylon that collapsed on Thursday, causing widespread power cuts for all of Northland.

Andrew said Transpower crews were completing “routine maintenance” on the tower in Glorit.

“It is unprecedented and inconceivable that all the nuts were removed at once,” Andrew said.

“Our view is that the specifications and procedures [for the maintenance] were not followed”.

Almost 100,000 people were left without power.

Andrew said Transpower had appointed an external party to conduct a formal investigation into the fall.

She said she was grateful that no one was hurt in the incident and it was a “dangerous scene” when the tower fell.

“It is really important to us to understand what happened,” Andrew said when she was asked about speculation in the hours after the incident.

“Was there a saboteur? Was there corrosion issues? It’s really important to not jump to conclusions.”

Mornez Green, managing director of Omexom, the company completing maintenance on the power, said the incident was “unprecedented”.

“We removed too many nuts from the bolts that resulted in the tower falling over.

“Omexom promptly worked to restore the power.

“I can assure you we will be open and transparent in the investigation.”

Green said the competence of the people on site will be assessed during the investigation.

Green said he had been involved in many investigations in the past, including during Cyclone Gabrielle.

“We have to decipher what is fact and what is fiction.”

Green said there has been a “massive amount of effort and work” that has gone into restoring the power in Northland.

Green would not go into detail regarding the people involved in the maintenance that caused the tower to fall.

He said it was “very fortunate” that someone did not die.

The crew on the site were “stood down immediately”, Andrew said, and all base plate work was halted across the country.

For compensation for Northlanders who were without power, Andrew said people can make a claim through the Consumer Guarantees Act and go through their electricity provider

Mark Ryall, executive general manager of Grid Delivery, said any work that was more than “removing one bolt” needs an engineering review. He said he was “confident” in the reviews so far.

Ryall said an audit done recently was successful and showed no issues.

Ryall said there had to be at least one trained line mechanic on site at all times, and two others who had been “grid trained” in-house by Transpower.

Energy Minister Simeon Brown, meanwhile, promised there would be a full review into the “unacceptable” outage.

On top of Transpower’s own investigation, Brown said he would be asking the Electricity Authority to review the incident and he was considering a Government review.

Authority chief executive Sarah Gillies has confirmed it will be undertaking a review after the minister’s statement.

“Electricity consumers need to have confidence their electricity supply is as reliable as possible. Our review will seek that assurance on behalf of consumers,” Gillies said.

The transmission tower collapse, which happened in Glorit, Auckland, about 45km west of Warkworth, occurred at the same time another circuit connecting Northland to the grid was down for maintenance.

Raphael Franks is an Auckland-based reporter who covers breaking news. He joined the Herald as a Te Rito cadet in 2022.