Around 2,500 homes and businesses in north Belfast were left without electricity after vandals attacked a NIE substation in the Ballygomartin Road area.
Emergency teams worked overnight in an effort to restore supply following the incident at Lyndhurst Meadows in the early hours of Friday morning.
Police said they received a report around 12.20am that two bins had been pushed against the substation and set on fire.
A PSNI spokeswoman said they are appealing for anyone with information to contact police at Tennent Street on the non emergency 101 number.
Supply was restored to the majority of premises by 1.45am, with the final 200 customers back to normal by 7.30am.
Kevin McDowell of NIE Networks said: “Vandals are risking their own and other people’s lives by approaching substations and causing deliberate damage. There is live high voltage equipment inside, and interfering with it can be unforgiving.”
DUP MLA William Humphrey thanked the NIE engineers for their efforts, and added: “Those responsible need to take a hard look at themselves and recognise how much danger, inconvenience and expense they have caused.”