EirGrid is insisting that its controversial new GridLink project cannot be located underground.
The third phase of the public consultation process comes to an end today, but the power company insists that there is still no clear plan yet for the route of the infrastructure project which is meeting stiff opposition from communities across Munster and Leinster.
The company says there will be further consultation with the public before it even gets to the planning stage to erect hundreds of pylons.
But John Lowry - project manager on the GridLink project - said that the type of power generated and used here means that running the cables underground is not feasible.
"People are asking 'Why can't this be undergrounded?' - what we have on the transmission system is what we call AC [alternating current] electricity," he said.
"That's the electricity that is generated by every power station across the country, it's the power that comes into all of our homes, it’s the power that's utilised across every transmission system in Europe and right across the world.
"To do this project using that electricity is not technically feasible."
The government has been accused of emotional blackmail after warning that putting new power lines underground will mean higher bills.
Energy Minister Pat Rabbitte said that putting new lines underground will mean higher electricity bills for 50years.
Opponents of the pylon scheme have accused the Minister of undermining the public consultation process, which ends today.
Fianna Fáil's Dara Calleary says the Ministers' comments will interfere with the final decision.
"These objections are genuine," he said.
"They're based on health, they're based on genuine economic reasons as well. They will have to be assessed by An Bord Pleanála.
"And for the head of Government and members of the Government to dismiss these concerns prejudges what is supposed to be an independent, statutory planning process."