UNDERGROUND SERVICE on the Green Line was suspended for 2½ hours Tuesday morning when an overhead wire between Arlington and Copley Stations sustained damage that knocked out the system.

Thousands of riders spilled out of subway stations at about 8:20 a.m. and had to find other ways to get where they were going as service was shut down between Government Center and Kenmore in both directions.

An MBTA spokesman said buses were rushed into service while repairs were made but customers were also asked to use the Orange Line and commuter rail to reach their destinations. The spokesman said customers on only two trains, about 300 people, were stranded between stations and had to be escorted to the nearest subway platform. No injuries were reported, the spokesman said.

Officials said late in the day that the wire problem stemmed from the failure of an insulator in the overhead catenary system. “This section had been thoroughly inspected less than a week ago. The MBTA power department will keep working to identify the root cause of the failure,” a T spokesman said in an emailed statement.

The incident was another reminder of how fragile the MBTA’s system can be with its aging equipment and power systems. In February, the derailment of a Red Line train at Andrew Station snarled the morning commute. The cause of that incident has never been officially explained.

Gov. Charlie Baker, who is running for reelection this year, has said his goal is to get the T into working shape but much of the equipment he is counting on to help do that is not scheduled to arrive before voters head to the polls in November. Jay Gonzalez, who is seeking the Democratic nomination for governor, planned to ride the Green Line after 5 p.m. to talk to riders about problems on the T.