Electricity network company Orion says last week's strong aftershocks in Christchurch damaged at least 70 underground cables.
It expects it will take two months to repair the 11,000 volt cables.
Most of the faults are around the Avon River in the east of the city, and at Sumner.
In comparison, February's earthquake damaged more than 200 11,000 volt cables - with many suffering multiple faults - along with four 66,000 volt cables.
Orion says last week's aftershocks have not significantly delayed efforts to repair the cables damaged in February, which should be mended by late July.
Nearly 1000 homes in Avonside and Bexley have been relying on three diesel generators to supply power since last week.