Commuters faced delays for the second straight day yesterday during rush hour after smoke shut down the 7 line for more than 90 minutes.

The disruption to the line came a day after power failures to the Lexington Avenue line shut down service three times Tuesday and angered already weary riders.

About 750 riders were trapped on the 7 trains yesterday morning at 6:45 when smoke was detected and power to the line was automatically shut off. Transit officials said the smoke came from an improperly secured metal plate that was jarred loose by the vibrations from passing trains and made contact with the third rail. Though there was no fire, the smoke shut off electricity to the trains, one of which was passing through the Steinway tube, which is the tunnel beneath the East River that connects the 7 line from Queens to Manhattan.

Power returned at 7:45 a.m. with full service restored at 8:21 a.m.

The disruption angered commuters already shell-shocked from Wednesday’s disruption along the Lexington Avenue line when water that seeped through a hole above a subway tunnel below Park Avenue South at 33rd Street damaged cables carrying electricity to train’s signals along the Lexington line. The third delay, also caused by water damage to cables at the line’s stop at Grand Central Terminal, came amid the evening rush hour at 5:22. Service was restored at 6:15 p.m., transit officials said.

The 2-by-3 foot hole where water first seeped out is man-made, transit officials said, though who made it remains under investigation.

The water damage to the cables underscored the subway’s aging infrastructure, the chairman of the city council’s transportation committee, Council Member John Liu, said. It also highlighted the need for the state authority’s $27 billion capital plan to be fully funded by the governor and state legislature.