A contractor who accidentally drove a piling into underground power cables while putting in a sidewalk caused the 41/2-day blackout downtown, the utility says.

The contractor had asked for plans showing where the cables were, but the Seattle City Light maps didn't show the service line that was hit, said Gerald Garman, assistant superintendent of the city-owned utility.The contractor, Granco of Redmond, was not at fault, Garman said Wednesday.

"Obviously, we're not happy with it," Garman said. At the time the line was installed, he added, "officials didn't have the data fetish they have now."

Utility engineers are double-checking the accuracy of other maps, he said.

The piling struck a live wire and touched off the short circuit that sparked the Aug. 31 fire in an underground vault and the 50-block blackout.