In a small section of Piedmont, a golf community of 1,500 homes just north of Haymarket, the lights kept going out.

Beginning July 27, the power shut down for nearly 400 customers four times over 21/2 weeks.

The cause of the outages was a mystery for the Northern Virginia Electric Cooperative (NOVEC), which serves nearly 70,000 customers in Prince William County. "The one at Piedmont got us baffled a little bit," said Allen Barbee, assistant vice president of system operations for the cooperative.

It was a frustrating can't-run-the-air-conditioner, can't-use-the-computer problem for homeowners. "The biggest issue is the heat," said Kathy Stark, who has lived in the subdivision for more than three years.

Stark said her friends with home businesses were not only left in the dark and the heat, but were temporarily out of work. "When your electricity goes out for an hour, you're obviously not working," she said.

After two weeks of probing and failed fixes, Barbee said, NOVEC solved the mystery: A lightning arrestor -- a piece of equipment that protects aerial power lines from lightning -- was itself struck by lightning.

That caused a short in the power line, but the problem was clearing itself, allowing power to run most of the time, Barbee said. The outages were all less than three hours. "Occasionally, it would fail," he said.

The $50 lightning arrestor was replaced last week. "The smallest things can cause the major problems," Barbee said.

NOVEC is continuing to monitor the line. It also plans to install more lines to its Catharpin substation to feed more power to Piedmont.

The $280,000 project should reduce the number of outages in the subdivision, he said. "It's kind of like adding another lane to a highway. You are actually adding capacity to the infrastructure," Barbee said.

The subdivision gets power from two substations, Catharpin and Evergreen, which is on Route 15, also known as James Madison Highway. That's why 400 customers can be without power and 1,000 others can have no interruptions, Barbee said.

Roxanne Lumme, 43, a homemaker in the subdivision, said she often wondered why her electricity would go out and a friend in the community would be running appliances as usual.

Lumme said the outages have been short but "annoying."

She said she had no stories about "having a big dinner party ruined." But an outage did interrupt what she calls "quiet time," the time her two young children watch television. She kept them entertained.