The commercial operation of one of the biggest energy projects in the history of the state has been deferred after testing revealed it was affecting phone lines.
Households in north county Dublin reported buzzing, noise and interference on landlines after the official opening of the east-west interconnector.
The 500-megawatt cable runs beneath the Irish Sea from Wales and then underground from Rush, Co Dublin, to Meath.
Eircom said investigations identified the faults may have been related to the state-of-the-art infrastructure.
"Both parties are aware and are working together to identify what exactly is the scale and scope of it," said a spokesman.
The commercial operation of the interconnector was due to start on October 1, after it was built ahead of schedule for 570 million euro.
Officially opened a month ago, it was the single biggest energy infrastructural investment since the commissioning of the hydroelectric Ardnacrusha power station in Co Clare in 1929.
The connection can be used to export excess energy generated here to markets in Britain, or to import it into the state. But an Eirgrid spokesman confirmed its operation was delayed when testing started.
Complaints were made from households in Ballyboughal, Oldtown and Rush - where residents had campaigned for years against the cable running through the town.
"During testing the power line successfully transferred on both direction at full capacity," he said. "Some localised telephone interference was reported during the course of that testing and further tests are taking place. There are no telephones affected at present because it isn't being operated commercially."