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Human error led to massive power outage in downtown Seattle

By Casey McNerthney
By Casey McNerthney

Human error – described as an “oversight” in a Seattle City Light briefing – led to the massive power outage that left thousands of customers in the dark May 25.

Quick facts:

  • Roughly 12,000 Seattle City Light meters were affected during the May 25 outage.
  • Human error was the cause.
  • Locations that went dark included: Pike Place Market, Seattle's tallest building Columbia Tower, and Seattle Public Library.
  • Outage started about 11:30 p.m. Lasted about an hour.

“We have determined that an oversight during testing of newly installed equipment was responsible for the outage,” Larry Weis, City Light CEO and general manager, said at a briefing Thursday, eight days after the outage.

Weis later said the agency determined the “oversight” cause earlier in the week. He said the agency wanted to be certain about the cause. He didn’t say specifically why city leaders waited eight days to explain that human error cut power to 12,000 downtown Seattle customers.

He also said no one would be fired because of the mistake.

“We apologize to everyone affected and inconvenienced by the power outage,” Weis said.

City Light only charges for electricity used. Weis did not say if businesses interrupted during the middle of their work day would receive any kind of compensation for the roughly hour-long outage.

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He said crews were testing new relays that were installed at the Massachusetts substation and worked with older relays. A relay is a device that senses changes in electric current and the signals the circuit breakers to protest equipment from surges and faults.

“When a crew tests relays, some of the breakers are locked so that they do not sense test signals from the relays and do not open,” Weis said. “In this instance, our crews blocked out the primary breakers, but overlooked the backup breakers.

City Light is already halfway through an effort to install test switches for all substation relays, Weis said. That work is part of the agency’s strategic plan initiative to upgrade infrastructure is expected to reduce some of the complexity involved in the testing that led to the outage, Weis said.

Cox Media Group

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