More than 3,000 homes were without electricity for more than an hour yesterday.
The blackout affected not only homes and businesses in the Withdean and Hollingbury areas of Brighton, but also traffic bollards and traffic lights to the north of the city.
Seeboard said the fault was at a sub station in Withdean.
Power went off at 4.30pm and was restored by 5.45pm.
Seeboard spokesman Claire Byrd said: "Seeboard apologises for any inconvenience it caused."
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