Marine cable

The marine cable is approximately 385km long.

The majority of the project concentrated on routeing the subsea high voltage direct current (DC) cables from Ardneil Bay in Ayrshire, Scotland to a landfall point at Leasowe on the Wirral. The marine cable is approximately 385km long and passes through International, Scottish, Northern Irish, Isle of Man and English and Welsh territorial waters. As well as being the longest 2,200MW (megawatt) capacity HVDC (high voltage direct current) cable in the world, it is the first subsea link to use a DC voltage level of 600,000 volts (600kV). 

There are two cables, which in shallow waters (less than 40 metres) have been laid in a paired bundle. In deeper waters the two cables have been laid separately, typically at a distance of 30m apart.

The cables have been buried approximately 1.5 metres below the seabed for the great majority of the route. At crossings with existing cables and pipelines, or where seabed conditions prevent burial of the cables, they have been laid on the seabed and covered by rock armour to protect them from damage.

The cables have been laid in approximately 120km sections connected by cable joints.

Work completed in 2017

In early 2017, we brought the marine cables ashore in Scotland. This was done in a slightly different way than the cable-pulling operation in the southern section carried out in 2014 (see section below) because of the difference in water depth. For a leaflet describing the work in Scotland please see here and to see footage of the operation please see here.

We then completed the remainder of the marine cable-laying and connected the marine cables to the land cables in Scotland and Leasowe, Wirral.

Work in 2015 and 2016

In 2015 and 2016 we continued with our surveys as required and began the main cable-laying at sea, moving from Liverpool Bay northwards.

In Scotland, we completed the work to pull both pipes from the working barge to our temporary compound at Portencross Road.

Work to the end of 2014

Our main marine work in 2013 was to prepare for bringing the cable ashore under the sea wall and common at Leasowe.

In October 2014 we completed the operation to lay the first 36km of the cable system (comprising three bundled cables – two power and one fibre optic) under the sea wall at Leasowe, Wirral, and out into Liverpool Bay.

The cables were pulled under the sea wall through pipes that we installed in 2013. For more information on this work view the press release here or the fact sheet here or to see time lapse photography of the operation see the video below.

Time-lapse video

During 2014 we also started preparations to bring the cable ashore at Ardneil Bay, North Ayrshire. This involved using a working barge, anchored a few hundred metres from the shore, and a drilling machine on land to drill horizontally under the golf course and beach.  At the end of the year, we started installing the first of two 600-metre long plastic pipes through the drill hole we had created, pulling the pipe from a barge moored offshore. 

During both 2013 and 2014 we also periodically carried out UXO surveys along the cable route in Beaufort’s Dyke using Remotely Operated Towed Vehicle (ROTV) and Remotely Operated Vehicle (ROV) equipment. We also carried out a trial of the main marine cable burial system in several areas along the cable route.