SWISS power company ABB has signed an $800 million (£497m) contract to install a 100-mile (160km) cable under the Moray Firth to link up north-east Scotland's power network.

The cable, travelling underground and in trenches on the seabed, will be equipped to bring 1.2 gigawatts, or roughly enough to power 960,000 homes, of renewable energy into the grid by 2030.

"It's a true breakthrough, it's the biggest investment in the Scottish grid for 40 years," said ABB chief executive Ulrich Spiesshofer as he unveiled the contract in London yesterday.

Scottish Hydro Electric Transmission, a subsidiary of SSE, applied last year to build the link, which is set to cost a total of £1.2bn to construct.

In July, energy regulator Ofgem gave the green light for the project, deeming it "the right first step to reinforce the network in northeast Scotland".

As well as hiring ABB, Scottish Hydro plans to bring in other contractors by the end of the year to work on the project, which is due to be finished in 2018.

ABB will put in place a high voltage direct current cable between new converter stations at Blackhillock in Moray and Spittal in Caithness.

The cable will give the growing number of tidal, wave and wind power projects in the region extra capacity to feed into the grid.

The Scottish government has set a target of 100 per cent of the country's electricity coming from renewable sources by 2020.

Mr Spiesshofer said yesterday he did not see any risks to the contract from next week's referendum.

More details on jobs are expected once all the contracts are awarded, but SSE has previously said 600 jobs will be supported during construction.

ABB said it has installed the vast majority of cable links of this kind in the world. "This is where ABB is leading," said Mr Spiesshofer.

The firm is also working on a link for the MeyGen tidal stream project in the Pentland Firth, having won the contract last month.

The Caithness-Moray cable is not the first of its kind in the country. Scottish Power and the National Grid hired Siemens and Prysmian in 2012 to install a 249-mile (400km) cable between Hunterston in Ayrshire and the Wirral peninsula.