Transpower advises that at 4:32pm there was a failure at the Otahuhu substation which caused a momentary voltage dip in the upper North Island. All Transpower's equipment remained in service and supply was maintained.
Transpower Chief Executive Patrick Strange said the incident would not have been noticed by the majority of end use customers.
"The most noticeable effect would have been a flicker of the lights. Some more sensitive large users of electricity may have briefly disconnected in response to the voltage dip."