DETROIT (AP) _ Crews struggled for the second day Wednesday in the steamy heat to restore power to Detroit city buildings, schools, police stations and jails after the century-old municipal power system failed.

The outage, which began Tuesday afternoon, trapped people in elevators and on elevated trains and turned some intersections into traffic free-for-alls at rush hour. School ended early, city workers went home, court hearings adjourned unexpectedly and inmates were put on lockdown.

Police reported no crime or traffic accidents related to the outage during the night.

``We felt pretty lucky that no one was hurt,'' said Gregory Bowens, a spokesman for Mayor Dennis Archer.

The 911 emergency system in the city of 1 million was not affected.

Bowens said he could not predict when electricity would be fully restored to the 4,500 buildings, 87,000 street lights and 1,250 traffic signals powered by the city Public Lighting Department.

``The reality is, the backup to the backup failed and that never happened before,'' he said.

Residential and business customers supplied by Detroit Edison in the nation's 10th-largest city did not lose power.

By 9 a.m. Wednesday, crews had restored 70 percent of the electricity to 1,400 city- and county-owned buildings, all primarily in the downtown area, plus traffic lights, Bowens said. But classes Wednesday for 170,000 public school students were canceled.

``We've heard some grumbling in the hallways from other employees. One of them said the temperature in his office was 89 degrees. And they've turned off the down escalator,'' assistant city ombudsman Stina Santiestevan said.

With a high of 88 degrees Wednesday, Santiestevan didn't say how hot her office was. ``I'm not sure we want to know,'' she said. ``But it was my luck, I had to wear a suit today to the City Council meeting. I told them, `Watch out _ I may show up tomorrow in shorts and a halter top.'''

Detroit City Airport's tower operated with emergency receivers, but passengers had to be searched with hand-held metal detectors instead of the walk-through kind.

Repairs on one of three lines that connect the Public Lighting Department to Detroit Edison were under way when a second failed Tuesday, the mayor said. The remaining line could not handle the load, and the city's entire generating system shut down.

Detroit Edison said it warned the city to scale back power usage Monday after the first line failed. ``They were in the process of doing that, but it didn't happen quick enough,'' spokesman Scott Simons said.

Much of the electricity used in the outage's early stages came from generators the city had bought as a hedge against the Y2K computer bug, which caused far fewer problems than feared.

``Y2K turned out to be this big nothing,'' Bowens said. ``But the one and a half million dollars the city spent on generators turned out to be money well spent.''

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On the Net:

City of Detroit: http://www.cit.detroit.mi.us

Detroit Edison Co.: http://www.detroitedison.com