Georgia Power spokesman Jeff Wilson said the company is still investigating the cause of the Monday morning blast. He said it could take a few weeks to determine what happened.
The explosion blew off manhole covers and knocked power out for hours to many stores and homes. No injuries were reported and there was only minimal property damage.
The affected area included River Street, the site of many of Savannah's tourist attractions, shops and restaurants.
Georgia Power is in the second year of a $50 million five-year upgrade in the underground power network downtown.