The project
Latest update – October 2026
We have now received planning permission for three of the four main elements that make up this project.
This includes permission to:
• Install underground cables, a new shunt reactor and other infrastructure at Trawsfynydd Substation. Work here is now underway.
• Lay new and replacement underground cables at Pentir Substation. Work will begin here in summer 2027.
• Replace the existing electricity cables beneath the Glaslyn Estuary and connecting the cables to our Eryri Visual Impact Provision’s project's site at Minffordd. Preparatory work is now underway, and we currently expect to start the main work in spring 2027.
We are also seeking planning permission to build a new substation south of Bryncir off the A487.
Following conversations with the North and Mid Wales Trunk Road Agent (NMWTRA) and Cyngor Gwynedd, we have relocated the site’s access road approximately 275 metres further east along the A487 in our design.
We now plan to submit an updated planning application to Cyngor Gwynedd in December 2026.
We will also need to replace the wires on one side of the overhead electricity line between Bryncir and Trawsfynydd, to increase the amount of electricity this part of the network can carry. We expect to begin this work in late summer/early autumn 2028.
Our current activity in the area
Ahead of the main construction work to replace the existing underground cables at Porthmadog and beneath the Glaslyn Estuary, we need to carry out some preparatory works.
This preparatory work is now underway and includes creating temporary construction compounds.
The first compound we are building is located on the former golf driving range off the A498, south of the Tremadog roundabout. It will be used as a base while we build our main construction compound on the opposite side of the road. This means you may see us transporting equipment and materials to and from this site over the coming months.
The smaller compound will remain in use until the main compound has been built, and the main compound will then remain in place until the end of the project. The main compound will include staff offices, welfare facilities, equipment storage and ‘laydown areas’ for temporarily storing materials.
National Grid needs to reinforce and refurbish parts of the existing high voltage power network in North Wales. This work is part of The Great Grid Upgrade- the largest overhaul of the grid in generations.
Enabling a clean energy future for Wales
National Grid needs to reinforce and refurbish parts of the high voltage power network in North Wales.
The way electricity is generated in the UK is changing rapidly to more secure, cleaner, home-grown energy from more affordable sources.
It is predicted that demand for electricity will at least double by 2050 as we shift to clean energy to heat our homes, drive electric vehicles and power our industry.
The Welsh Government wants to meet the equivalent of 70 per cent of Wales’s electricity demand from renewable energy sources by 2030.
The existing transmission system was largely built in the 1960s and was designed to connect electricity mainly generated in coal-fired power stations to homes in Wales and England.
To allow new sources of renewable energy to be connected to the network, we need to reinforce and refurbish the existing electricity network between Pentir and Trawsfynydd. This will help to keep the network secure by enabling more clean energy to be delivered to homes and businesses.
This is a major project, and it is essential that the strengthened connection is in place by 2030.
This is part of The Great Grid Upgrade, the largest overhaul of the electricity grid in generations, comprising 17 major infrastructure projects across Wales and England. Progress towards green electricity is the most effective way to ensure energy affordability, with homegrown renewable power expected to help to lower energy bills in the long term.
You can read more about our work and our latest plans here.
Keeping the community updated
We want to work closely with local communities, landowners, businesses, statutory bodies and elected representatives to help minimise any disruption as this essential project takes place.
Ahead of the main construction beginning in summer 2027, we will issue a project update newsletter that will include more details of the work. We will also organise community events, to make sure people have another opportunity to talk to us directly, meet the project team and ask any questions.
This pre-construction update will mark the start of our ongoing community engagement programme, with regular updates, conversations and events taking place throughout the construction phase.
If you have any questions in the meantime, please do contact us using the details on the right-hand side of this page.
Contact us
If you have any questions about the project, you can get in touch in the following ways:
- Call us on: 0800 915 2485
- Send an email to: [email protected]