Last week more than 100,000 people were left without power after a Transpower pylon fell when contractors removed too many nuts from bolts connecting the tower to a base plate.
Contact said more than 20,000 of its customers were impacted by the outage.
"For us, it's about doing the right thing. We have a responsibility to keep the lights on, and when our customers are impacted by incidents out of their control, we need to step up and do the right thing," said chief executive Mike Fuge.
Starting from Thursday, Contact's Northland and Far North customers would receive a text message, or email, advising them of the refunds.
The refunds would be automatically included in their next bill.
Contact said its main priority for now was making sure its customers were fairly compensated.
Any claim processes would be followed up "in the coming months".
Security of supply fully restored
Transpower on Wednesday evening said it had "restored full security of electricity supply into Northland" with the installation of "additional temporary structures and returning the second 220 kV circuit to service".
"Restoring the second circuit was more complex given its position under the fallen tower," Transpower executive general manager grid delivery Mark Ryall said.
"Our crews have managed to transfer the conductor to the three additional poles erected over the last few days. Northland now has full security of power supply with this circuit returned to service."
A new permanent tower was next on Transpower's list, he said.
"That design work has started already. The temporary structures are sufficiently robust and resilient to provide for security of supply until the permanent fix is in place."
Transpower was conducting its own internal investigation into what led to the old tower's fall, as well as cooperating with the Electricity Authority's separate probe, he said.
RNZ
