BOSTON (CBS) -- Power is now back on for the customers affected by a blackout Sunday morning.
As of 10:30 a.m. power was back to all except a few buildings.
Another power outage is planned for 4-hours overnight after midnight, so crews can fix the substation.
At the height of the blackout, 12,000 customers were without power.
It happened around 3:15 a.m.
The problem is with the Scotia Street substation. This is the same station that was to blame for a blackout in the Back Bay in March, last year.
The affected area was roughly Copley Square to the Charles River and Kenmore Square to Columbus Avenue.
The Massachusetts Turnpike was closed at the entrance of the Prudential Tunnel because the outage was affecting lighting and ventilation in the tunnel.
On Sunday night, the state Department of Transportation announced that the Prudential Tunnel would be closed from 1 to 5 a.m. Monday morning to help NStar repair the substation. Eastbound traffic was set to be detoured at Exit 18 on the Mass Pike to Storrow Drive, although trucks would be sent on an alternate route. Westbound Mass Pike traffic was set to be detoured to Interstate 93 south then to Massachusetts Avenue.
WBZ NewsRadio 1030's Kim Tunnicliffe reports
Scotia Street Substation To Blame For Back Bay Blackout
The tunnel reopened around 11 a.m.
The Blackstone Community Center opened at 10:30 a.m. to provide cool shelter and power to those that need to charge electronic devices.
Mayor Tom Menino is urging anyone with questions or problems to call his 24-hour hotline at 617-635-4500.
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