It’s not clear what caused 5,000 NStar customers to briefly lose power in Cambridge this morning, NStar spokesman Mike Durand said.

The power went out at 9:45 a.m., though service was restored to all customers at about 10:15 a.m., Durand said. Crews are investigating an issue on a nearby transmission line as a possible cause, he said.

In a message posted on Twitter, Cambridge police said officers helped to direct traffic at intersections with inoperative signals in East Cambridge.

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