Thousands of Whanganui residents were left powerless for a brief period yesterday - the second time in three days homes and businesses were blacked out.

But while both faults were traced back to the Peat St substation in Aramoho, electricity supply company Powerco said the cuts were unrelated. Around 6300 properties across parts of the central city, Aramoho, Springvale, St Johns Hill and Westmere lost power between 7am and 8am yesterday due to a fault on a 33kV line connect to the substation.

Phil Marsh, Powerco network operations manager said it was a fault on an 11kV line that caused an outage. It affected around 2500 customers in Aramoho, Springvale, St Johns Hill and Westmere who are supplied by the Peat St substation. Mr Marsh said the cause of the faults was being investigated.