SEPTA shut down service on its busiest Regional Rail line Saturday, stranding more than 300 passengers for hours on the Main Line and forcing Amtrak to halt service between Philadelphia and Harrisburg.

The pantograph on the roof of a Paoli-Thorndale train — that’s the mechanism that connects the train to overhead power lines — got snagged with cables as the train approached 30th Street Station at about 3:30 p.m. Saturday, said Andrew Busch, a SEPTA spokesperson.

Amtrak, which operates the line, cut power on the Paoli-Thorndale line and stranded four SEPTA trains in service. Amtrak also halted service on its Harrisburg rail line, which runs adjacent to the SEPTA Main Line tracks.

SEPTA announced early Sunday morning that service had been restored on the Paoli-Thorndale line.

More than 300 passengers on four SEPTA trains were stranded for up to 2½ hours as SEPTA dispatched shuttle buses to the rescue. Trains were stuck in Ardmore, Wynnefield, Overbrook, and Merion.

“It took a while to scrounge up some bus operators to get out to the four locations,” said Busch.

Inconvenienced passengers took to social media to complain they had not been informed by the transit agency about the cause of delays. Busch said SEPTA would review its communications procedures.

Only service on the Paoli-Thorndale line was halted, but the disruption rippled out to other Regional Rail lines Saturday afternoon, causing some delays, Busch said.

The Paoli-Thorndale line is SEPTA’s busiest route, carrying about 20,000 passengers on weekdays, and about 11,000 to 12,000 passengers on a typical Saturday.