Transpower and Vector have appointed a three person panel panel for a technical investigation into the Auckland power cut this week.
The blackout started on Sunday after a fire at the Penrose substation.
Eighty five thousand homes and businesses were affected with some without power for two days.
The companies have appointed industry experts Bob Simpson, a former Chief engineer with Transpower, Ian McBurney, an electrical engineer, and Brian Gregory, who is a world expert in cable systems.
The investigation is expected to take about four weeks.