There are three independent sections of the NIMT which are electrified: Auckland's urban network and the central section (25 kV AC) from Palmerston North – Te Rapa (north of Hamilton) at (25 kV AC).
Wellington's urban network is electrified at (1500 V DC); as formerly used in other sections of the New Zealand network.
In Wellington the operating voltage has been increased to 1700 V DC since the full introduction of the Matangi EMU, to increase the power available.

Electrification of the NIMT was mooted by electrical engineer Evan Parry in the first volume of the New Zealand Journal of Science and Technology in November 1918.
In light of a national coal shortage following World War I, Parry argued that the network was under great strain due to ever-increasing volumes of freight, and the use of steam traction was partly to blame.
Parry also noted that there was great potential for cheap hydro-electricity generation in the central North Island to power electrification.

The first part of the NIMT to be electrified was the Wellington–Paekakariki section via the Tawa Flat deviation that was completed on 24 July 1940.
This was largely to prevent smoke nuisance in the 4.3 km No.
2 tunnel, and to provide for banking on the Paekakariki to Pukerua Bay section.
Electric traction in this section is now used only by Transdev Wellington for Metlink suburban passenger services on the Kapiti Line, and was extended to Paraparaumu on 7 May 1983 and Waikanae on 20 February 2011.
Funded by the Greater Wellington Regional Council, the extension to Waikanae coincided with the delivery of new FP class Matangi electric multiple units.

Following the Second World War railway services suffered due to skill and coal shortages.
Skilled staff sought employment opportunities elsewhere in the economy.
From 1948 to 1951 the General Manager of the Railways Department, Francis William Aickin, advocated electrification of the entire line, despite protests from his engineering staff.
Aickin had previously been Staff Superintendent and Chief Legal Advisor to the Department and considered using diesel locomotives for trains on the NIMT to be too expensive.
He turned his attention to electrification, mainly because he saw that it could relieve the coal situation and prevent high expenditure on imported fuels.

He commissioned a study into electrification, which concluded that a low-frequency AC system could be cheaper than 1500 V DC, the system in use in Wellington.
Aickin sent a technical mission of four senior officers overseas in March 1949 and travelled overseas himself to negotiate a tentative contract with a British construction company.
The Chief Mechanical Engineer and Chief Accountant specified and costed the system and Aickin was able to complete a substantial report justifying the NIMT electrification and submit it to the Government.

Officers from New Zealand Treasury and the Ministry of Works and two experts from Sweden (Thelander and Edenius) commented on the proposal and in December 1950 the Government granted approval in principle and agreed to appoint Thelander as a consultant.
However, Aickin fell out with the then National Government and retired as General Manager in July 1951.
With the change in regime, the electrification proposal disappeared.

A key assumption of Aickin's report was that traffic on the NIMT would grow by 50% from 1948 to 1961.
Since a diesel-electric locomotive is a travelling power station, the savings through electrification compared to diesel could be regarded as the difference between the cost of buying bulk electrical energy generated substantially from New Zealand resources and the cost of generating electricity in a small plant using imported diesel fuel.

The Royal Commission on Railways created following Aickin's tenure rejected the report's findings.
Aickin's successor, H.C. Lusty, revised the tentative contract with English Electric to specify DF class diesel-electric locomotives.
They were later found to be unreliable, and only ten were supplied.
42 Dᴳ class locomotives were supplied instead for secondary lines.
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There are three independent sections of the NIMT which are electrified: Auckland's urban network and the central section (25 kV AC) from Palmerston North – Te Rapa (north of Hamilton) at (25 kV AC). Wellington's urban network is electrified at (1500 V DC); as formerly used in other sections of the New Zealand network. In Wellington the operating voltage has been increased to 1700 V DC since the full introduction of the Matangi EMU, to increase the power available.
Electrification of the NIMT was mooted by electrical engineer Evan Parry in the first volume of the New Zealand Journal of Science and Technology in November 1918. In light of a national coal shortage following World War I, Parry argued that the network was under great strain due to ever-increasing volumes of freight, and the use of steam traction was partly to blame. Parry also noted that there was great potential for cheap hydro-electricity generation in the central North Island to power electrification.
The first part of the NIMT to be electrified was the Wellington–Paekakariki section via the Tawa Flat deviation that was completed on 24 July 1940. This was largely to prevent smoke nuisance in the 4.3 km No. 2 tunnel, and to provide for banking on the Paekakariki to Pukerua Bay section. Electric traction in this section is now used only by Transdev Wellington for Metlink suburban passenger services on the Kapiti Line, and was extended to Paraparaumu on 7 May 1983 and Waikanae on 20 February 2011. Funded by the Greater Wellington Regional Council, the extension to Waikanae coincided with the delivery of new FP class Matangi electric multiple units.
Following the Second World War railway services suffered due to skill and coal shortages. Skilled staff sought employment opportunities elsewhere in the economy. From 1948 to 1951 the General Manager of the Railways Department, Francis William Aickin, advocated electrification of the entire line, despite protests from his engineering staff. Aickin had previously been Staff Superintendent and Chief Legal Advisor to the Department and considered using diesel locomotives for trains on the NIMT to be too expensive. He turned his attention to electrification, mainly because he saw that it could relieve the coal situation and prevent high expenditure on imported fuels.
He commissioned a study into electrification, which concluded that a low-frequency AC system could be cheaper than 1500 V DC, the system in use in Wellington. Aickin sent a technical mission of four senior officers overseas in March 1949 and travelled overseas himself to negotiate a tentative contract with a British construction company. The Chief Mechanical Engineer and Chief Accountant specified and costed the system and Aickin was able to complete a substantial report justifying the NIMT electrification and submit it to the Government.
Officers from New Zealand Treasury and the Ministry of Works and two experts from Sweden (Thelander and Edenius) commented on the proposal and in December 1950 the Government granted approval in principle and agreed to appoint Thelander as a consultant. However, Aickin fell out with the then National Government and retired as General Manager in July 1951. With the change in regime, the electrification proposal disappeared.
A key assumption of Aickin's report was that traffic on the NIMT would grow by 50% from 1948 to 1961. Since a diesel-electric locomotive is a travelling power station, the savings through electrification compared to diesel could be regarded as the difference between the cost of buying bulk electrical energy generated substantially from New Zealand resources and the cost of generating electricity in a small plant using imported diesel fuel.
The Royal Commission on Railways created following Aickin's tenure rejected the report's findings. Aickin's successor, H.C. Lusty, revised the tentative contract with English Electric to specify DF class diesel-electric locomotives. They were later found to be unreliable, and only ten were supplied. 42 Dᴳ class locomotives were supplied instead for secondary lines. Fo
North Island Main Trunk