Utility: Flawed sensor wiring played key role in NYC blackout

(Photo by Michael Appleton/Mayoral Photography Office)

Electrical utility Con Edison says it's figured out more details about why a relatively small problem escalated into a big blackout in Manhattan earlier this month.

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 says 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.