Speaking before the Joint Oireachtas Communications committee on Tuesday, Slye said undergrounding would not be a practical solution for the interconnector, costing €500m more than pylons.

"Undergrounding is three times more expensive," he said. "As a State body, this is a cost that is not acceptable and cannot be passed on to the consumer.

"The public should not have to pay for the cost of undergrounding when there is no enhancement of service."

Groups in the area had been campaigning for power cables to be placed underground as part of EirGrid's upgrading of the country's energy infrastructure. However, a recent report said that this is not an option for the North South route and now Slye has moved again to confirm this.

He said there are also additional complications involved with undergrounding the North South interconnector. EirGrid has been liaising with Bord Pleanála and landowners on the issue.

"We have liaised with landowners and are inviting them to speak to us. They can make submissions when the public consultation opens," added Slye.

EirGrid will be opening offices in Cavan, Meath and Monaghan and Slye said member of the public can visit to express their concerns or ideas on the project.

EirGrid's upgrade of the network is called Grid25 and a recent report found that one of the routes, Grid West project in Mayo and Roscommon, could potentially run underground cables for a short distance. It was asked at the meeting why this solution was offered only in Grid West.

"In Grid West we found if the voltage was reduced, we could underground 30km of the project," he said. "We are also looking at undergrounding for Grid Link (in the south and east of the country).

"That analysis has been submitted to a panel and we will examine the different options and consult with communities as part of the Grid 25 review. All options must meet regional needs."

Slye said the plans for a 400kv overhead line have already been submitted to Bord Pleanála.