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One of the workers, employed by lines company Connetics, received an electric shock when a 11kv line being moved came into contact with a live 33kv line.
The worker was retrieving parts from a truck "energised" for between one and two seconds.
The investigation — a duty holder review for WorkSafe NZ — was carried out by the company, and a partially redacted version was released to the Otago Daily Times.
The crew travelled to Millers Flat from Cromwell .
About 10am an elevated work platform bucket was being used to transfer de-energised 11kv conductors between two poles when the conductor contacted a live 33kv conductor about 1.2m above.
This caused the "inadvertent livening'' of the 11kv conductor and subsequent energisation of two work vehicles.
The worker who received the shock was observed shaking his hands after the event.
He was examined by ambulance staff and cleared of any medical impact, the review said.
Seven witnesses heard the clash of conductors, and all field staff "stayed put'' while assessing the situation.
No workers were wearing insulated boots provided by the company and required to be worn.
The review found there was an "element of complacency" and all the company's workers had been alerted to the footwear requirement.
The review noted the order of tasks being done was out of sequence, and as a result an observer was not in place watching the lines being shifted.
This, the review said, constituted a "human error mistake that resulted from deficiencies or failures in the workers' judgement process".
Also, earthing equipment was in place but "wasn't installed at a depth to be fully effective''.
The line being worked on belonged to Aurora Energy Ltd and the live line to Talla Burn Generation Ltd.
One response to WorkSafe said it was "usual practice'' to work below live conductors and the risk had been discussed before the work began.
"The workers doing this task ... believed they had plenty of clearance but this wasn't the case''.
The review noted all workers held the correct training and competency for the work and there was a "significant level'' of experience within the work team.
The company's chief executive John Thompson declared the improvements identified in the review had been implemented or were to be implemented by specific dates.