The two power outages that stranded more than 1,000 riders on two stuck trains and delayed thousands more on the Red Line on Wednesday were caused by unrelated failures, according to Metro.
The transit agency said the outages had different causes, neither of which was related to commercial power from its provider Pepco.
The first outage between the NoMa and Rhode Island Avenue stops was caused by work being done to upgrade the power station there, Metro spokesman Dan Stessel said. Metro had done extensive trackwork in that area over the weekend just days before, but Stessel said it was not related.
About 60 riders trapped on an outbound train there during the meltdown had to be evacuated along the trackbed, then ferried by shuttle buses. All other Red Line trains had to share a single track around the area.
The second outage, which that happened within about an hour of the first. occurred between Friendship Heights and Tenleytown. That trapped a packed eight-car train with some 1,000 people aboard for more than an hour underground.
That one appears to have been caused when a safety device called a protective relay tripped because four eight-car trains were passing through the area, drawing too much power for the relay's setting, Stessel said. The device needed to be adjusted to a higher setting to support that many trains, he said.
The agency had been staging power crews near those trouble spots after the meltdown. But since the causes have been determined, the agency has called them back to normal work around the system, Stessel said.