The wire came down at Trenton Station at 5:20 a.m. Monday, taking out two tracks into New York. It was fixed by 9:15 a.m.
Without the tracks, Amtrak trains operated as much as 30 minutes behind schedule.
NJ Transit spokesman Dan Stessel says NJ Transit's Northeast Corridor trains out of Trenton were up to an hour late for most of the morning rush.
Officials are trying to determine what brought the wire down.