A signal system at the DeKalb Ave. station in Brooklyn lost power at rush hour, knocking the B line out of service.
The B line from the Bronx to Brooklyn was entirely shut down, scrambling service and causing extensive delays on six other lines — the C, F, N, Q, R and W lines.
Brooklyn D line riders, meanwhile, were unable to get to Manhattan, as trains dumped riders out at the 36th St. station.
Southbound D trains were rerouted to the C line in Manhattan and the F line in Brooklyn.
John Raskin, director of the Riders Alliance, said the rush hour woes shows that the subway is deteriorating.
“If Gov. Cuomo doesn’t show a little leadership and step in to fix transit, it’s going to be the 1970s all over again,” Raskin said. “To many riders, it already feels that way.”
Con Edison spokesman Sidney Alvarez said there was a “voltage dip.” The utility company got no report of a power outage, he said.
Con Ed sent crews to the area near the station to pinpoint the problem, according to Alvarez.