Properties in Cromford were among the 30,000 homes and businesses across Derbyshire to have had their power cut off after an explosion at an electricity substation.
Traffic lights along the A6 between Cromford and Matlock also stopped working as a result.
Firefighters were called to the explosion at the substation, on the B5056 near Winster, yesterday at about 1pm.
Electricity network Western Power Distribution had restored power to about 20,000 customers by 5pm, a spokeswoman for the company said.
She added it could be “a matter of days” before the remaining 10,000 homes had electricity.
The Western Power spokeswoman said the substation fire was out by 5pm but the building had to be assessed for structural damage before an investigation could start.
She said it could be a “couple of days” before the cause of the fire was known.