NEW YORK, July 15 (Xinhua) -- The massive power outage in New York City on Saturday was caused by a malfunctioning relay protection system, the utility company Con Edison said in a statement on Monday.

In a preliminary review of the incident, the power service company said that a relay protection system at the West 65th Street substation did not operate as designed.

The system failure did not isolate a faulted 13,000-volt distribution cable nearby, which "ultimately resulted in isolation of the fault at the West 49th Street transmission substation, and the subsequent loss of several electrical networks," said the statement.

The company said it is continuing with the investigation.

About 72,000 customers in Midtown and Upper West Manhattan lost service during the blackout that started at 6:47 p.m. (2247 GMT) on Saturday. All customers had their power restored in five hours.