There is an option to extend the alliance for a further five years.
The contract, which is part of one of the largest procurement exercises undertaken by National Grid, will support their increased investment in the electricity transmission network and contribute to long-term security of supply.
The works are required to connect new infrastructure such as wind farms and new generation plant to the grid. They will also cover the enhancement and replacement of existing assets.
The contract, which will come into force in March 2007, is one of two overhead line and four sub-station contracts due to be signed by National Grid in the coming weeks.