UPDATE, 4:08 p.m.:
Crews have determined that the almost hour-long power outage in South Anchorage was caused by two substations not communicating correctly, said Sarah Wiggers, Chugach Electric spokeswoman.
A crew was working on the Retherford substation, off of Old Seward Highway between Dimond Boulevard and O'Malley Road, when a relay tripped a switch that was already open at the Sand Lake substation, she said.
"It was quite a little chain reaction," Wiggers said.
UPDATE, 11:25 a.m.:
All power was restored at 11:15 a.m., but crews are working at the Sand Lake substation to see why power went down for nearly an hour, said a Chugach Electric spokeswoman.
About 6,300 South Anchorage customers have been without power since 10:18 a.m. Monday, according to Chugach Electric Association.
The outage affects those served by the Sand Lake substation, said Sarah Wiggers, Chugach Electric spokeswoman.
She said two crews are investigating the problem but the cause is still unknown.
The outage area is stretches from Minnesota Drive to Lake Otis Parkway and from O'Malley Road to 64th Avenue, she said.
The outage also cut power to several traffic lights on Dimond Boulevard, she said. The Municipality of Anchorage reported in a Twitter post that traffic on Dimond was moving "very slowly" and recommended use of alternate routes.
CHECK BACK FOR UPDATES ON THIS DEVELOPING STORY.