[5] Following its initial construction, the twin 66 kV transmission lines connecting the power station with Christchurch's Addington substation were the highest voltage in New Zealand, and the longest at over 100 kilometres (62 mi) long.

[3][6] In the early years of the station, demand for electricity in Christchurch grew rapidly[4]: 125–145  and the transmission system extended to reach Rangiora in the north and Oamaru in the south.

[4]: 145–158 [2] By the early 1930s, Coleridge had reached capacity, and was supplemented in 1934 by the commissioning of the Waitaki Dam and in 1935 by extending transmission lines south to join Coleridge/Waitaki to Dunedin's Waipori scheme.

One subsidiary, Transpower, adopted responsibility for the outdoor switching yard, with the parent company planning to sell the facility at Coleridge.

[4]: 116  These inlets supply water to two horseshoe-shaped[2] tunnels which run almost horizontally (grade of 1:1000)[4]: 111  through approximately 2.2 kilometres (1.4 mi) of the hill between the lake and the power station.

These tunnels terminate in large concrete surge chambers above the power station, which in turn connect to the distinctive steel penstock pipes that run down the hill above-ground to the turbine hall.

[1] Coleridge was the first station in the world to use aerated draft tubes on the turbines, invented on-site by Silston Cory-Wright to solve an issue with heavy thumping when under load.

The open-air switching yard supplies 66kV lines that run both east (connecting to the Transpower switch yard at Hororata and from there on to Christchurch) and west (across the Southern Alps via Arthur's Pass to supply the West Coast).