Norwich ― The power outage that knocked out power to more than half the city Friday evening occurred when a large bird, likely a great blue heron, struck three wires at a Norwich Public Utilities substation and shorted out the system, NPU officials said Tuesday.

The outage knocked out power to 11,775 of NPU’s 22,000 customers for nearly two hours, prompting police to direct traffic at key intersections with dark traffic signals.

“This scenario is exceptionally rare, and there is no recollection of a similar outage occurring on the NPU system over the past 25 years,” NPU spokesman Chris Riley said Tuesday.

NPU released a photo of the dead bird beneath the three exposed pipes that carry the wires, each carrying 13.8 kilovolts of electricity. The pipes are 2 feet apart, so the bird had to have at least a 4-foot wingspan to touch all three pipes at the same time, Riley said.

National Geographic list the great blue heron wingspan at 5.5 to 6.6 feet.

Riley said NPU is investigating whether the pipes can be wrapped with insulation to prevent future accidents.

Claire Bessette