We're installing new underground power cable

A secure and resilient power network is essential, so we're strengthening our electricity network

Our work on SH76 Brougham Street

As part of our project to install a new 66kV underground power cable from Bromley Substation to Milton Substation, we installed cable ducts along Brougham Street from Ensors Road to Burlington Street, between November 2023 and February 2024.

In February and March, we installed the new power cable through the ducts from the Milton Substation on Milton Road, along Burlington Street and Brougham Street to a joint bay between Wilsons Road and Opawa Road. We have one final section of cable to install from this joint bay along Brougham Street and Ensors Road to Sullivan Avenue.

We've started work on Ensors Road digging a trench the new cable, and traffic management is in place. The cable will pass through ducts on Brougham Street that were installed in 2023, and there will be further work around the joint bay between Wilsons Road and Opawa Road. Brougham Street will be open while we work, and traffic management will be in place.

Our works on Brougham Street and Ensors Road are due to finish in June 2024. Once this final section is complete, we will have installed 7.5km of new underground power cable, strengthening our electricity network.

Thank you to all residents and road users who have been affected by our works, we appreciate your patience and understanding.

Installing the new power cable

Once all cable ducts are laid in the road, we install the new power cable.

The new cable is pulled through the ducts between two joint bays. Each length of cable is around 800m long and arrives on a large drum, 4.5m in diameter and weighing 27 tons.

The new cable is pulled through the ducts using a winch. We pull the cable through the ducts carefully as the cable is heavy and not very flexible. Once all the lengths of cable are installed we join the cables together at the joint bays.

In February and March 2024 we will be pulling the cable through the ducts on Brougham Street and Burlington Street. We'll then join the sections of cable together.

Bromley to Milton project background

Some of our underground cables in Christchurch City are 40-60 years old. These older cables are still working, and will continue to do so under normal conditions. However, they are vulnerable to earthquakes and should we have another large earthquake, there is the potential for faults on these cables. Given the age of the cables they are difficult to repair, and after a significant shake these cables could take some time to fix.

Replacing these cables to strengthen our network is a major programme of work for Orion. One of the first projects is installing a new underground cable from Bromley Substation to Milton Substation. This new power cable is the first of 12 new cables that will create new ring circuits in Christchurch City. These ring circuits have two purposes:

• They allow us to shift power around the network. This means that if there is a fault on the network we can re-route the power to keep customers on.
• Once the new cables and circuits are in place we can progressively retire the old cables as the power will be supplied via the new circuits.

The new cable uses the latest cable technology and is sized to accommodate future growth.

Where are we working, and when?

We’re installing a new underground 66kV power cable from Bromley Substation to Milton Substation. The new cable is installed in the road.

We started construction on the new power cable in November 2022. It will take us about 18 months to install the cable along the 7.5km route from Bromley to Milton Street. The cable will be laid in nine stages or work areas - see map below.

What does our work involve?

The new 66kV cable will be installed in a trench in the road. On Brougham Street, we’ll be digging a trench in the road and then installing cable ducts. Ducts are plastic pipes that we thread the cable through later.

After we have installed ducts, we reinstate the road surface and the traffic management is removed. Ducting allows us to speed up the cable laying process and reduce impacts on traffic.

Once the ducts have been laid, we return to install the new power cable in around 800m lengths. The cable arrives in large drums, each weighing around 27 ton. The cable is threaded through the ducts using a winch. We then join the sections of cable together at joint bays.

We’re also building a new switching station at our Milton Substation. The new cable will feed into the switching station. It gives us the ability to switch between power circuits meaning that we have alternatives in the event of an outage and can restore power more quickly. See more details below.

How do you install the cable?

Stage 1 - Traffic management set up We need to have traffic management in place to safely install power cable into the road. This includes fencing the work site and temporarily changing traffic flows.	Stage 2 - Removal of the road surface The first step of the construction process involves breaking up the road surface. A milling machine is used to remove the paved layers of the road.	Stage 3 - Excavation of the trench Next, we dig a trench to install cable ducts into. We use hydro-excavation, where pressurized water breaks up the soil, to work around existing services.
Stage 4 - Installing cable In some places we install the cable in ducts in the road. The ducts are plastic pipes that we thread the cable through later. If we aren't using ducts, we lay the cable in the trench.	Stage 5 - Filling in the trench The trench is backfilled using fine crushed rock. A compactor machine is then used to compress the contents of the trench and fill in air pockets.	Stage 6 - Road surface repair Once all the ducts are laid and the trench is backfilled, the road’s surface - or paving - is repaired.
Stage 7 - Removal of the traffic management After the road has been reinstated, the temporary traffic management is removed.	Stage 8 - Cable pull Three cables are installed into the ducts in each trench. They are carefully winched along the trench, from one joint bay to the next. Pulling the cable is difficult as it is heavy and not very flexible, and we want to avoid damaging it.	Stage 9 - Cable jointing We install sections of cable in 600-800m lengths, and join the sections together at joint bays. Once the cables are joined together, we then fill in the joint bays and repair the road surface in this area.
Milton Switching Station The power cable will connect into a new switching station at the Milton Substation on Milton Street in Sydenham. A switching station allows us to switch between power circuits meaning that we have alternatives in an outage and can restore power quicker. It will be housed in a purpose-built, secure building next to Faraday Street. Construction is currently underway.	This is how the new switching station could look.

How will this work affect me?

This is a construction project so homes, businesses, and community facilities along the cable route will be impacted while we install the ducts and cable in the road. Road users will also be affected by the traffic management in place.

Overall traffic management

We're laying the new 66kV cables in the road and there will be traffic management in place to enable us to do our work safely. The traffic management set up will change as move along the cable route, and could include:

There will be no on-street parking available where we are working.

Power supply

There will be no disruption to the power supply to install the new cables. However, along some parts of the cable route we may need to relocate some existing underground power cables. To do this work safely there may be power outages for some customers. You will be notified of any power outages by your power retailer.

During the day, vehicle access to properties on the side of the road where we are working may be temporarily restricted while we trench past. We’ll place steel plates over the trench, so residents and businesses can access the property when we’re not working.

Rubbish collection

Your rubbish will be collected as normal. If we are working outside your property, please place your rubbish bins out to the kerb as normal. The crew will move the bins for collection if necessary and return them to outside your property.

The story of Ōpāwaho

On the outside of the new switching station building we have worked with a local Ngāi Tāhu artist who has designed a special art piece for the outside of the building. This tells the story of the natural environment of Ōpāwaho/Heathcote River which was an important mahinga kai area, or source of plentiful food, particularly tuna (eels), pātiki (founder), and inaka (whitebait). Ōpāwaho was also an important travel route connecting peninsular settlements with Ōtakaro and north to Kaiapoi. Click here for more information on the design. The artwork on the new building draws inspiration from the tukutuku – a geometric pattern that acknowledges the importance of mahinga kai and the links to the Port Hills and the rivers. We're also planting native trees and shrubs around the switching station, to enhance biodiversity, and provide food for birds and insects. It’s really exciting to be working with mana whenua to share their stories through our infrastructure. You will be able to view the art from Faraday Street once the switching station is complete.

What are the benefits of this project?

These works are essential to powering a cleaner and brighter future with our community. Installing the new power cable and switching station will strengthen the resilience and security of the power network and provide for the future growth of our city.

The network will be stronger in a major earthquake and we'll be able to restore power quicker.		The new cable will be another circuit supplying Christchurch. If there is a fault on the network we will be able to keep more customers on and restore power quicker.		The new cable is sized to cater for our growing demand for power.