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An Aurora Energy spokeswoman said the surge in Millers Flat happened while contractors were doing maintenance on a transformer about 2.30pm yesterday.
The work caused a secondary fault and voltage surge.
"Thankfully no-one has been hurt, although we understand the power is still off for some properties in Teviot Rd and surrounding area."
Aurora had also been advised there was damage to electrical equipment in some properties, the spokeswoman said.
Twenty-one customers were affected by the outage and houses were inspected one by one to make sure it was safe before power was restored.
All houses were expected to have their power back on by last night.
Customers who had damaged equipment were asked to contact their insurance company in the first instance, she said.