One of two power transformers at the Transpower Edgecumbe substation is out of service for emergency repairs, reducing the security of supply to most of the Whakatane district.
In a statement Horizon Networks said while emergency repairs were being carried out, there had been no impact on customer supply.
Transpower expects the transformer to be back in service and the security of supply restored by Friday.
While on one transformer there is a very low probability of a failure on the remaining transformer.
But should an event occur, customers can expect an extended outage of supply.