Transpower is looking to make a key investment into the Cook Strait electricity cable. 

It's consulting on a $1.4 billion upgrade to the 610 kilometre link connecting the North and South Island.

The existing cables are likely to reach their end of life in the late 2030s. 

Major Electricity Users' Group Chairman John Harbord told Ryan Bridge the link's important when hydro-lakes in the South are low in water.

He says the North Island's often moving forms of renewable electricity down to the South Island.

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