S.F. Blackout Blamed on Human Error and Mechanical Failure
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SAN MATEO, Calif. — The San Francisco blackout that affected more than 1 million residents was triggered by a combination of mechanical failure and human error, Pacific Gas & Electric Co. said Wednesday.
Investigators from PG&E; continue to probe the causes of the Dec. 8 outage that shut down San Francisco and parts of San Mateo County.
Investigators said PG&E; workers performing system upgrades at a substation correctly connected 18 safety ground wires, but neglected to remove six of them when they re-energized the lines.
The oversight led to huge power oscillations at the work site and the failure of a safety system designed to prevent such fluctuations.
Investigators must still examine other possible breakdowns in a meticulous and detailed process.
To prevent a repeat of the outage, which lasted for hours, PG&E; has repaired the failed system and implemented a backup of the backup system that went down.
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