Thousands of homes in Ripley and Heanor were left without power when metal thieves targeted a substation last night.
Electricity was lost in more than 32,000 properties at around 11.30pm after earthing cable was taken in the Heanor area.
Parts of Moorgreen in Eastwood were also affected.
Power was restored by energy suppliers Western Power Distribution (WPD) within six minutes, a spokesman said.
It marks the second incident in a week where a power cut has been caused by metal thieves.
The WPD spokesman said: “Metal theft is a nationwide problem but it has escalated in the last few years and is currently costing Western Power Distribution around £1.5 million a year to put right.
“We’re stepping up our security with CCTV, anti-vandal paint, Smart water and intruder alarms, and we’re working closely with the police at a local and national level. We’ve also recently issued a booklet which identifies all our cables and which is designed to help police and scrap dealers.
“Prosecutions have taken place and have led to prison sentences. We will always prosecute.
“We’ve also used a range of media including television, radio and newspapers to deal pro-actively with this issue, as well as Crimestoppers.”