The Estlink 1 power cable, one of two electricity connections with Finland, will be turned on again on Saturday.
Both Estlink cables failed around September 10, near doubling electricity prices in Estonia, although the Estlink 2 cable was restored a few days later.
Estlink 2 is likely to be switched off soon to complete repairs, which were put off until Estlink 1 was working again.
The Competition Authority began an investigation into the failures, which pushed electricity prices from around 37 euros per megawatt hour to 65 euros.
“The simultaneous failure of both links has meant a significant price increase for customers. For that reason the authority will investigate if Elering's actions have been in line with regulations,” Märt Ots, the head of the authority, said.
The investigation will focus on the reasons of the failures. It will also ask whether the failures could have been prevented.