Power has been restored after it was cut to more than 6000 Whanganui properties, including Whanganui East, Gonville, Castlecliff and some in the central city on Friday morning.
The outage occurred at 7.45am with power returning by 8.15am.
A Transpower spokesperson said the system was inadvertently tripped during routine upgrade work at the Whanganui substation.
Transpower is following up the cause to ensure it doesn't happen again and apologised for the sudden outage.
"We were pleased we were able to get it on quickly, because there was a crew close by."
