Trucks parking on Omahu Rd may have contributed to the failure of six power poles which collapsed across a busy Hastings road last month, cutting power to businesses and homes for most of the day.
Power company Unison Networks said its investigation would be completed by the end of next week.
Customer care and relationship manager Danny Gough said initial indications were that one of the poles had failed, coming down and triggering a domino effect, pulling over the other poles early on December 21.
"Our discovery to date is that there are marks on the poles which indicate something has come into contact with them," he said.
"There are large trucks parking along there which may have made contact with the pole and we believe that has compromised the integrity of the pole over time," Mr Gough said.
All power poles, including those on Omahu Rd, had been tested before the incident and were found to be fine.
"We have gone about re-testing all of the remaining wooden power poles on Omahu Rd to make sure there are no further incidents and we are confident there won't be," he said.
"But we want to do the testing to ensure the public there are no concerns."
Unison invested more than $40 million on capital works each year to ensure the longevity of the network, to make sure any failure was minimised.
"This was a very rare failure but we are taking it seriously. We had power poles that came down on a busy road in the middle of the day, so we want to make sure no stone is unturned in our investigation."
Mr Gough said Unison was able to supply power generators to those who were without power during the day the poles came down, impacting on the industrial and residential areas of Frimley.
"We were limited to what we could do because we need those generators for emergencies or key customers, like health providers and emergency services."
In a separate incident on Monday, a fire on a power pole in Crosses Rd, near Havelock North, cut electricity to 546 customers in the Arataki area about 5.45am.
Unison said the power was restored to most customers in under five minutes and the remaining customers were connected within 15 minutes.
The damaged power pole was replaced on Monday evening.
The fire started because of a build-up of pollutants, such as pollen and dust, on the insulators.