Horahora-Waikino 50 kV transmission line

Engineering Work (eg road, bridge, sawmill, dam)

This was the earliest line in the national grid. It ran from Horahora Power Station (which was flooded when Lake Karapiro was formed) to the Waihi Gold Mining Co stamping battery in Waikino.

The Waihi Gold Mining Co in the Coromandel was the largest single industrial user of electricity in New Zealand between 1900 and 1920. It first began generating its own power in 1896, with an upgrade in 1902 to be able to run the huge stamp battery. Additional generating capacity was added in 1905. However, to expand the mine, a cheaper supply of electricity was needed. At last in 1908, after protracted negotiations, the company was granted a licence “to generate up to 10,000 hp at the Horahora Rapids on the Waikato River, and to transmit the same to Waihi”. Work on the project began right away, both on the powerhouse and on the transmission line.

The line was 51 miles (82 km) long between Horahora and Waikino substation where the voltage was reduced to 11kv for transmission the last few miles to Waihi. At the northern end the line crossed the Te Aroha ranges. Over this section, bush was felled and burnt to a 4 chains (80 metres) width, and a graded bullock track formed to enable materials to be moved to the tower sites. The Company decided that the line was to operate at 50kV. This decision set a precedent for the subsequent quite large network of 50kV lines in the North Island.

Steel towers were chosen (not wooden poles which the Public Works Department used for the Lake Coleridge system which was being built about the same time). Pin type insulators were used. These towers were spaced about 500 feet (150m) apart except over the Ranges where the spans were more uneven owing to the very rough nature of the ground.

The wiring for most of the line consisted of three solid, hard drawn copper wires (No.0, SWG, 0.324 inches diameter, weighing 1,678 lbs per mile). But over the Ranges, the “best hard-drawn bronze” trolley wire, 0.45g inches diameter, weighing 3,366 lbs per mile was used. Telephone wires were carried on the same .towers below the power wires. These used hard-drawn bronze wire, l00 lbs per mile. For the distribution line from Waikino to the Martha Mine in Waihi, the wires were 37/13SWG bare, hard-stranded copper cable, weighing 5104 lbs per mile.

For operational and maintenance a patrolman’s cottage and halfway station was established at Stanley Bridge 23 miles from Horahora. Every five miles along the route, telephone huts equipped with the necessary repair tools were built. Each tower along the route was numbered and had a danger notice attached to it, a practice that still continues.

By the end of 1912, nearly all the towers were in position, but the industrial action at Waihi in 1912 had delayed progress on the line and northern terminal stations. The whole transmission scheme was finished and testing of equipment completed by the end of 1913. Official inspection of the system by Evan Parry, Chief Electrical Engineer of the Public Works Department and by the District Inspector of Mines followed.

Horahora hydro station was completed in early February 1914, and its power was delivered to the Waihi mines on 8 April, 1914.

This was a well-planned and designed scheme which was to prove very reliable.

A celebration to raise one of the refurbished towers was held at The Waihi Arts Centre and Museum site on 6 March 2010. This was part of a larger project, coordinated by the Waihi Museum, to restore four transmission towers.


No Attachments

The line ran from Horahora Power Station to Waikino on the Coromandel.

Thames Valley / Coromandel, Waikato

Access Info
The tower in the photograph below is thought to be located in the vicinity of the Karangehake Gorge Historic Walkway. (www.doc.govt.nz)

Nature of Engineering
Electrical Power Generation and Distribution


I R Robinson effecting maintenance up the tower, while supported at the base by A E Davenport (later General Manager of NZED) and Mr MacLennan (later District Electrical Engineer, Hamilton), circa 1924.

(Click image to enlarge )