Built by Brush Traction in Loughborough, England between 1986 and 1988[1] to run on the new electrified central section of the NIMT, at 3,000 kilowatts (4,000 hp), they are the most powerful locomotives to operate in New Zealand.

Following the oil shocks of the 1970s, the National government, led by Prime Minister Robert Muldoon, launched the "Think Big" energy development projects.

One of the projects involved the electrification of the 411-kilometre (255 mi) central section of the NIMT between Palmerston North and Te Rapa, approved in 1980.

The 2,050-kilowatt (2,750 hp) DX class diesel-electric locomotives, then the mainstay of the NIMT and only recently introduced themselves, could handle 720-tonne freight trains on the section, but could only average 27 kilometres per hour (17 mph) when climbing the 1 in 52 gradients of the Raurimu Spiral.

[5] The electrification of the central section began in 1984, with the government setting aside NZ$40 million to purchase a fleet of 25 kV 50 Hz AC locomotives to operate the new electrified line.

These lines draw electricity from New Zealand's national grid at four locations along the electrified section: Bunnythorpe, Tangiwai, Taumarunui, and Hamilton.

[1] The EF class were nicknamed "Toasters" or "Shoe Boxes" by New Zealand railway enthusiasts due to their boxy shape.

[9] The EF class were first used to haul freight trains along the central section of the NIMT, with the completion of electrification in 1988.

After two years in service, two locomotives were withdrawn due to transformer failures, and converters were found to be unreliable and required replacing.

[8] Prior to the Stratford–Okahukura Line being mothballed usual operating practice was for the services originating from Auckland or Hamilton and Stratford to meet at Taumarunui and exchange trains there, with an EF regularly hauling the Hamilton-Taumarunui-Hamilton legs.

The EF's were not used initially on the Northern Explorer, KiwiRail experimented for a short while with towing the whole consist – including the diesel locomotive – over the central section.

Despite the NIMT railway electrification and the Auckland railway electrification being built to the same voltage specifications (25kV AC at 50 Hz), the EF class could not be used on Auckland's network due to that network requiring higher fault current tolerances than the NIMT.

From June 2006, the locomotives have been fitted with AAR couplers, each weighing over 400 kilograms (880 lb), to allow them to pull heavier trains.

EF's 30036 and 30088 were withdrawn from service following a derailment caused by a washout at Oio (north of Raurimu) on 7 August 1991 that also killed the locomotive engineer.

[14] After recovery from the site, the two heavily damaged locomotives were stored at Hutt Workshops until the decision was made that it was both uneconomic to repair the units and they would be surplus to existing requirements.

[20] Following the 2017 general election KiwiRail and the new Labour-led Coalition Government announced on 30 October 2018 that capital funding would be made available to refurbish 15 of the locomotives at the Hutt Workshops, extending the service life by 10 years for their continued use on the NIMT electrification in line with the new Government's energy and emissions policies.

[21][22] EF30226 and EF30163 were transferred to the Hutt Workshops via the Wairarapa Line in November 2019 for overhaul by KiwiRail in collaboration with original manufacturer Brush Traction, now a subsidiary of Wabtec.

[29][30] After extensive testing and ironing out of issues with its control system, EF30163 began hauling revenue services in November 2022.