18 January 2021

Entrust has an agreement with Vector where they are committed to spend an average of $10.5 million each year to develop and install new or innovative technologies for the electricity network, undergrounding or improving remaining overhead power lines.

Trustees Dr Paul Hutchison, William Cairns (Trust Chairman) and Alastair Bell reviewing progress on the Mt Albert undergrounding project

The Mt Albert undergrounding project, bound by Oakley Creek, New North Road, Carrington Road and Unitec, consists of 16 streets, with a combined street length of 5.4km, 166 poles and benefitting 867 customers. It is a significant project and will result in the removal of 10.2km of overhead electricity lines. The project commenced in October 2019 and is expected to be complete in mid-2021.

How was this area selected?

This area in Mt Albert was chosen for undergrounding based on a number of factors.
When Vector prioritises undergrounding projects, they take into consideration factors such as the condition of the existing electricity lines and equipment in the area, their capacity, the frequency of faults, the suitability of the land (e.g. rock), the number of customers who will benefit, and the level of other utility works able to be coordinated at the same time, such as fibre or street lighting.

Where possible, Vector aims for a ‘dig-once’ approach, so residents benefit not only from underground power services, but also potentially from telecommunications, street lighting and pavement upgrades, resulting in an all-round visually enhanced street appeal at the end of the project.

The undergrounding process

The first part of the process is to build the new underground electricity reticulation network through trenching and drilling to install the cables. New ground mounted cabinets are also installed to displace the equipment previously installed on the poles, such as switchgear and transformers.

Once complete and tested, the network is made live and technicians begin to connect houses one by one to the new underground network. For the Mt Albert project, Vector also worked at the same time with Chorus technicians to convert each house to the underground fibre network.

Once all houses are connected, Vector can start de-energising and removing the overhead network, installing new streetlight stands and removing the old overhead lines and poles. The final touches are to reinstate footpaths and grass areas on affected berms and properties.

Encountering volcanic rock

In Mt Albert, there is a lot of volcanic rock close to the ground surface. This meant that in some areas, crews were prevented from using modern trenchless technology, like thrusting and directional drilling, which are typically faster and less disruptive. Instead, the team often had to dig trenches with diggers and rock breakers to get the new underground services down deep enough to ensure they are well protected. As you would expect, encountering a lot of rock means timeframes and costs can also increase.

An example of some of the rock found in the area that crews are trenching through.

Crews also brought in specialist ground penetrating radar to determine the depth of the rock before excavation, so they could determine the best way to undertake the work, and with the least amount of disruption to residents.

A crew member using a ground penetrating radar to measure the depth of the rock underneath the pavement to help decide the best method to install the cables.

The team

It takes a large crew to pull off an undergrounding project of this scale. Vector provides project ambassadors, who frequently communicate with residents and property owners about the project, how they will be impacted, and timeframes. Working closely with the community is very important to Entrust and to Vector.

Other people involved include civil workers, who undertake the trenching and drilling work, and electricity and fibre technicians, who install, connect and then liven the new underground electricity and fibre networks and house connections. Vector also has contractors to repair pavements and place topsoil and grass seed on berms and properties where required.

Pictured are Edmar (Electrician) and Melissa (Project Ambassador), ready to chat with Mt Albert residents about converting overhead powerlines to underground cables.