About 750 homes in the Mexborough area were left without power after thieves broke into an electricity substation unit.
Police were alerted to a break-in at the unit on Harlington Road, Adwick-upon-Dearne, at about 3.20am on October 2.
Thieves had stolen steel covers and tried to cut through cables, meaning many homes did not have their power restored until 7.15am that morning.
Acting Insp Wayne Goodwin, a metal theft specialist, said: “Offenders who target live sites are not only risking their own lives for something of very little value but their crime can cause wider disruption.
Mick Hickling of Northern Powergrid said: “The cable they have attempted to take is worth very little, yet the cost of repairing the damage is significant.”
Anyone with information about the incident is asked to call South Yorkshire Police on 101, quoting incident number 89 of October 2, 2013.