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Cable Laying Starts for Celtic Interconnector Project

7th August 2025
The cable laying vessel Calypso is docked at the Port of Cork in preparation for the Celtic Interconnector project's cable laying campaign
The cable laying vessel Calypso is docked at the Port of Cork in preparation for the Celtic Interconnector project's cable laying campaign.

A landmark moment was reached this week on the Celtic Interconnector project, as laying of the submarine cable commenced on the key energy project linking the electricity grids of Ireland and France.

The next phase of the project was signalled by the arrival of the specialist marine vessel Calypso, which will lay the high voltage direct current (HVDC) cable for the project, which is being developed with EirGrid and its French equivalent, Réseau de Transport d’Electricité (RTE) and co-funded by the EU Connecting Europe Fund.

When complete, it will be the first interconnector between Ireland and continental Europe, travelling from east Cork to the north-west coast of Brittany.

Pictured L to R are Michael Behan, Chief Financial Officer, EirGrid, Kieran French, Engineering and Interface Manager, Celtic Interconnector, Captain Ivo Damiaan de Heji, Calypso / Van Oord and Shane Cooney, Onshore Project Manager, Celtic interconnector. Pictured L to R are Michael Behan, Chief Financial Officer, EirGrid, Kieran French, Engineering and Interface Manager, Celtic Interconnector, Captain Ivo Damiaan de Heji, Calypso / Van Oord and Shane Cooney, Onshore Project Manager, Celtic interconnector.

The vessel, which arrived from Norway into the Port of Cork, has started the cable laying along an 84km section of the route. When fully complete, the HVDC cable will span 500km from east Cork to the north-west of Brittany and will allow the exchange of 700MW of electricity, equal to powering 450,000 homes.

The cable is being laid onto the seabed by the Calypso, with burial works done by two further vessels.

The cable lay and burial operations are weather sensitive and are being carried out in summer, to align with the best weather conditions. Marine survey teams have mapped the seabed in advance of works to chart the optimal route for the cable, with EirGrid liaising with local fisheries and marine users throughout.

The HVDC cable which is currently being laid along an 84km section of the Celtic Interconnector routeThe HVDC cable which is currently being laid along an 84km section of the Celtic Interconnector route

Speaking about the marine campaign, Michael Behan said: “EirGrid is proud to welcome this latest phase of works on the Celtic Interconnector project, which really shows the progress being made on this key energy project for Ireland. This feat of engineering that will take place over the coming weeks is testament to the collaboration, innovation and care required to deliver this critical infrastructure. We remain grateful for the continued patience and support of communities, landowners, and stakeholders as we progress this project.”

The cable laying installation is just one element of this strategic infrastructure project being developed by EirGrid and its French counterpart, Réseau de Transport d'Électricité (RTE). The project’s onshore phase has seen approximately 10km of high voltage alternating current (HVAC) cable installed in roads, with HVDC cabling works currently being progressed.

Meanwhile, civil works at the project’s converter station, located at Ballyadam, near Carrigtwohill, are near completion, with internal fitouts of the converter hall progressing well.

Published in Undersea Cables
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Undersea Cables

Undersea cables are vital to Ireland's connectivity, facilitating high-speed internet, telecommunications, and energy transmission. These cables traverse the Irish Sea, connecting Ireland to the United Kingdom and continental Europe, and play a crucial role in global communications.

Submarine Communications Cables:
Ireland is strategically positioned along major transatlantic communication routes. Approximately 75% of transatlantic cables pass near Irish waters, underscoring the nation's significance in global data transmission.
These cables are typically as wide as a garden hose, with the filaments that carry light signals being extremely thin—roughly the diameter of a human hair. They are sheathed in layers of insulation and protection, with cables laid nearer to shore using extra layers of armoring for enhanced protection.

Energy Interconnectors:
In addition to communication cables, undersea interconnectors are being developed to enhance energy security and support the transition to renewable energy sources. The UK has approved the construction of five new subsea interconnector cables to boost the grid's flexibility amidst rising renewable energy. These projects will link the UK with wind farms in Belgium and the Netherlands, and connect England with Germany, Wales with Ireland, and Scotland with Northern Ireland. The cables, with a combined 6GW capacity, are expected to be operational by 2032, increasing the UK's total interconnector capacity to 18GW.

Security Concerns:
The strategic importance of these undersea cables has raised security concerns. Incidents in the Baltics have heightened awareness about the potential risks to subsea infrastructure. Ireland's historical neutrality and limited defense resources have led to calls for enhanced maritime security and defense investments, including modern surveillance technology and international cooperation. The government's response includes participation in EU security projects and collaboration with neighboring countries on maritime security.

In November 2024, a Russian spy ship, the Yantar, was escorted out of the Irish Sea by the Irish navy after it was found patrolling an area with critical submarine pipelines and cables. The vessel's presence heightened concerns due to its proximity to interconnector cables vital for internet services linking Ireland to the UK, operated by major tech companies such as Google and Microsoft.

Regulatory and Policy Framework:
The protection and maintenance of undersea cables fall under the jurisdiction of national governments, with private companies often responsible for their security. In Ireland, the Department of Communications, Climate Action and Environment oversees the regulation of telecommunications infrastructure, including undersea cables. The Irish Naval Service plays a role in monitoring and protecting maritime infrastructure, including undersea cables. Internationally, the United Nations Convention on the Law of the Sea (UNCLOS) provides a framework for the laying and maintenance of submarine cables, recognizing the "freedom of the seas" and the rights of coastal states.

Conclusion:
Undersea cables are indispensable to Ireland's connectivity and economic infrastructure. Given their strategic importance, ongoing efforts are necessary to ensure their protection and resilience against potential threats. This includes enhancing security measures, international cooperation, and adherence to regulatory frameworks to safeguard these critical assets.