Transpower's completed its investigation into the fallen transmission tower - which severed power to Northland in July

Nearly 100-thousand people were cut off in July, when a pylon toppled after maintenance crews unbolted three of its legs - at once.

The report's found the crew from Omexom did not follow standard practice - and two less-experienced work crew members weren't sufficiently supervised.

It shows the supervisor on-site was sandblasting the tower's legs - as a relatively inexperienced worker removed the bolts.

Omexom told Transpower an experienced crew would be doing it, but they had no formal training for the work they were doing.