Con Edison: Flawed sensor wiring played key role in blackout

Screens in Times Square are black during a power outage, Saturday, July 13, 2019, in New York. (AP Photo/Michael Owens)

Con Edison has figured out more details about why a relatively small problem escalated into a big blackout in Manhattan earlier this month, the electrical utility said Monday.

The utility had already explained that the July 13 outage happened after a protective system called a relay failed to isolate a faulty high-voltage cable. A relay essentially can trigger a circuit breaker to keep a problem contained.

On Monday, Con Ed explained why the relay system didn't work as expected: because of a flawed connection between some sensors and relays.

The utility said it has fixed the problem and is making sure it won't happen elsewhere in the electrical system.

The blackout affected thousands of people for about five hours along a 40-block stretch including Times Square, Rockefeller Center and other busy areas.


Since we issued our preliminary findings into the cause of the July 13th power outage on the West Side of Manhattan, we have conducted extensive testing of equipment and a thorough review into why our relay protection system did not perform as designed. Our engineers have determined the root cause and taken steps to prevent a recurrence.

As part of our investigation, we reviewed 15 years of operating data and took equipment out of service at our 65th Street substation to conduct diagnostic testing, which allowed us to simulate the event. We identified a flawed connection between some of the sensors and protective relays at the substation. We have corrected that condition.

Out of an abundance of caution, we have taken preventive measures by isolating similar relay equipment at other substations. We will analyze and test the equipment before we put it back in service. Our electrical delivery system continues to operate with multiple layers of relay protection.

The New York City grid is one of the most complex and technologically advanced in the world, with multiple layers of redundancy. In electrical systems, a relay detects abnormal conditions on the electrical delivery system and instantly sends signals to circuit breakers to open and isolate the problem. We are confident that we have identified the cause of the July 13th outage, and taken the corrective actions necessary to provide safe, reliable service for our customers.