The fire on Christchurch's Port Hills is burning under the high voltage power lines that connect Ashburton and Christchurch.
Transpower says it thinks a build-up of soot affected transmission yesterday, causing a circuit outage at its Bromley substation.
39,000 customers in the east of Christchurch lost electricity just before 2.45pm on Wednesday.
The local lines company, Orion, says it restored power within 25 minutes.
General manager, Steve MacDonald, spoke to Corin Dann.
