A block of Person Street, just east of the Market House, was closed for nearly three hours while crews replaced the scorched underground cable. A Public Works Commission official said the secondary power cable shorted out and then exploded at about 2:30 p.m.
Witnesses said smoke came billowing through street man holes.
A parking enforcement officer said she saw a chair outside the Hamburger Heaven restaurant shoot into the air.
"It's a good thing nobody was sitting outside when that happened," the woman said.
The PWC official said it was unclear what caused the shortage, but the cable was expected to be replaced by late Monday.
At least one business, Hamburger Heaven, will be without power until the repair work is complete.
Nobody was injured.