But the assurances of the California Independent System Operator and Rosemead-based Southern California Edison, the state's No. 2 electrical utility, failed to ease the worries of Industry-based businessman Jim Randall.

Randall, president of aerospace rivet manufacturer Allfast Fastening Systems Inc., said his plant in Industry already has lost power twice this summer, on June 27 and July 1. The incidents cost the company more than $100,000 per day in lost productivity and materials.

"It's been absolutely killing me," Randall said.

Allfast supplies rivets to military and commercial aircraft manufacturers, including The Boeing Co., Airbus S.A.S. and Bombardier Inc. Its vacuum furnaces heat metals to temperatures as high as 1,800 degrees Fahrenheit and can put considerable strain on local power circuits.

"When the power goes off, everything drops to zero, and it ruins the metal," Randall lamented.

Although Allfast's outages were isolated incidents, they demonstrate what can happen when local power usage overwhelms the equipment that delivers power from utility substations to commercial and residential customers.

On Sunday, about 2,100 SCE customers near the Via Verde Country Club in San Dimas and 4,600 customers in the Stevenson Ranch and Newhall areas lost power in what the utility said may have been heat- related outages. The outages were not caused by lack of power capacity but by a pre-emptive shutdown intended to keep equipment from failing, an SCE official said.

Edison spokesman Steve Conroy said extreme heat and humidity can cause the utility's equipment to overheat. Such issues are not unusual, but they tend to occur during late summer, which is traditionally much warmer than mid-July.

"Yes, we have had transformers that have been pushed," Conroy said. "Do they fail because of high demand? They can, yes.'

Conroy said SCE is taking steps to alleviate equipment stress caused by heightened demand. The company is also advising customers to temper their power use between 4 p.m. and 6 p.m. daily, when total power consumption usually reaches its peak.

He stressed the utility has enough power to meet expected demand this summer, however.

"There are a number of steps we're looking at. Will they result in less outages? The answer is yes, we hope so," he said.