[1] The transmission line forms the major part of a wider North Island Grid Upgrade project with a forecast cost to completion of $894 million.

[2] The line was a major enhancement to the National Grid and was designed to increase electrical supply and security to Auckland and Northland.

If upgraded to 400 kV operation, additional underground cables would be needed to connect Brownhill Road directly to Ōtāhuhu substation.

The project also increases the power transfer capacity into Auckland, and reduces the loading on the existing 220 kV Whakamaru-Ōtāhuhu and Huntly–Ōtāhuhu circuits, with a consequential reduction in the reactive support needed in the Upper North Island.

The overhead line terminates at a new substation at Brownhill Road, near Whitford, close to the south east Auckland urban boundary.

The final report of the Board of Inquiry accepted Transpower's proposal to use monopoles instead of lattice towers in this area, and this became a requirement as part of the resource consent conditions for the project.

The composition of the aluminium alloy 1120 used in Sulphur conductor includes copper, manganese, magnesium, zinc, iron, chromium and silicon.

The major advantage of the all aluminium alloy conductor over ACSR is its superior strength to weight ratio and its lower electrical resistance for the same cross-sectional area.

The Electricity Commission began operations on 14 September 2003, and it comprised six members, of which Roy Hemmingway was appointed as founding Chair.

A new regulatory environment took effect in April 2004, with the Electricity Commission now responsible for assessing grid upgrade investment proposals by Transpower.

The regulatory process for approval of the series of investment proposals and grid upgrade plans submitted by Transpower beginning in 2005 created significant tension between Transpower and the Electricity Commission, and led to political pressure by Government ministers for progress to ensure the security of electricity supply to Auckland.

The most vocal opposition group was New Era Energy Inc, which organized protests at Transpower initiated consultation meetings, fronted for media comment, co-ordinated submissions to the Electricity Commission and the resource consent hearings, and did fundraising for the legal expenses which would soon come.

The Electricity Commission under Hemmingway also organized meetings during this time for information dissemination about its processes, and to gather feedback from the public.

In April 2006, the Electricity Commission announced its intention to decline Transpower's investment proposal for the 400 kV line, on the grounds that it was not the most cost-effective solution.

Later that year, Hemmingway was not re-appointed as chairperson of the Electricity Commission when his term expired, and on his departure expressed frustration at the political involvement in the regulatory process.

This significantly reduced the cost of the revised proposal, but it also meant that the higher efficiency and capacity of 400 kV transmission would not be possible.

It also meant that the objectionable height and scale of the transmission towers would still remain, but they would be significantly overbuilt to handle the lower 220 kV voltages.

In November 2007, New Era Energy announced that it would seek a judicial review of the decision by the Electricity Commission to approve the project.

A Board of Inquiry was established to consider the designations and resource consents for the project and began hearings in March 2008, which ran through to October that year.