NEW YORK (CBSNewYork) – Con Edison says it has pinpointed the root cause behind the blackout this month on the west side.

Con Ed had said the lights went out July 13 because of a problem at its 65th Street substation.

A system that was supposed to detect and isolate a faulty cable didn’t work.

Con Ed says it examined the equipment and poured over 15 years of data before identifying a flawed connection between some sensors and protective relays.

More than 72,000 Con Edison customers, from Fifth Avenue to the Hudson River and the West 30s to 72nd Street, were plunged into darkness around 6:47 p.m. as a result.

The problem is fixed, and Con Ed says it’s taken preventative measures at other substations.