Thousands of people were left without electricity in one part of Derbyshire overnight after thieves stole copper wire from five sub-stations. It meant Central Network was unable to divert power through them when an underground cable failed.
Two thousand homes and businesses in the Ilkeston area were affected. Most have been reconnected but some homes were still without power on Wednesday.
Jonathan Smith of Central Networks said the thieves were risking their lives.
He said: "You've got to reckon that no matter how high the costs of copper are, it's not worth it if your life is in danger."
Derbyshire Police confirmed it was investigating the thefts from sub-stations in the Wood Street and Manners Road area of Ilkeston.
Officers believe the incidents took place at about 2000 GMT on Tuesday.