More than 2,000 homes in Bushey, Radlett and Aldenham were left in the dark last night during the latest in a series of power cuts.
The electricity supply was stopped shortly before 9pm while EDF Energy engineers repaired a fault in a substation.
Supplies were restored to 2,079 customers by 9.30pm, and to the remaining customers by 3.45am today.
An EDF representative said: "We do understand how much inconvenience any interruption to power can cause, and would like to apologise to all those who have been affected."
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