Cook Strait too strong for cables
Cook Strait’s ferocious currents have been lifting a ‘‘backbone’’ communications cable from the sea floor as the search begins for a heftier replacement.
Transpower – the state-owned enterprise that owns and runs the national grid – is now in the process of finding a company to supply up to 90 kilometres of fibreoptic cable to link the North and South islands.
Tender documents show the existing cable is too light and lifts from the seabed because of the strait’s high tidal flow. Burying the cables was not an option, as they were too close to the interisland electricity cables.
Transpower is now investigating the cost for either one or two cables that were at least three times heavier, ‘‘specifically designed for the conditions in Cook Strait’’.
The new cables, despite weighing up to 20 kilograms a metre, would also need to be flexible enough to contour to the sea floor.
In a statement, Transpower’s Cobus Nel said the two fibre-optic cables formed ‘‘part of our communications backbone’’.
‘‘From our annual inspections, we have identified that one of the Transpower fibre-optic cables’ condition is deteriorating, indicating that it is nearing end of life and a replacement strategy has been established (as per normal business practice with all our assets).
‘‘We have discovered certain sections of these cables are moving more than other sections, due to tidal movements in the strait: this has caused some corrosion in parts of the cable.’’
The cables were originally installed in 1992, and replaced in 2003.
One of the cables – or perhaps two if it was more cost-effective – would likely be replaced in the next one to two years, he said.