Northern Ireland Electricity (NIE) says vandals who broke into one of its high-voltage substations in north Belfast put lives at risk.
More than 150 homes were temporarily left without power on Christmas Eve as a result of the incident.
Engineers worked through the night to reconnect supplies.
Roy Coulter of NIE said the vandals had set a piece of equipment on fire and that children could have been in danger as the unit was left open.
"They really put a lot of people at risk here on a very cold night," he said.
"They also put themselves at considerable risk and the Fire and Rescue Service who had to put the fire out."