Jun. 23--Record electricity use in the Valley is prompting two members of the Arizona Corporation Commission to seek assurances from utilities that they are prepared to deal with what looks like will be a long, hot summer of electric demand.

In separate letters sent to utility executives Wednesday, commission Chairman Jeff Hatch-Miller and commissioner Kris Mayes said electric demand hit a record Tuesday -- unusually early in the summer air conditioning season. Peak demand usually doesn't occur until July or August when summer monsoons combine with high temperatures to cause the heaviest use of air conditioners.

"The Valley's power resources will be put to the test this summer as we contend with the constant threat of wildfires and continued possibility of record heat," Hatch-Miller wrote in a letter to William Post, chairman of Pinnacle West Capital Corp., parent company of Arizona Public Service Co., and Richard Silverman, general manager of Salt River Project. "The monsoon season has yet to arrive and our energy demand appears to be already running at a record pace."

Mayes also noted that electric demand has been "exceptionally high" in the Yuma area, where APS has only a thin capacity reserve, and a brush fire on the Barry M. Goldwater Range required a high- voltage power line to be shut down Wednesday, cutting power to Ajo for three hours.

In a letter to APS President Jack Davis, Mayes questioned whether the utility had underestimated peak demand this summer.

According to figures provided by the ACC and the utilities, the peak electric use in the Valley by customers of APS and SRP reached a record 10,200 megawatts Tuesday.

The utilities thought peak demand could reach as high 10,600 megawatts on Wednesday, but lower-than-expected temperatures and humidity cause the demand to peak at about the same level as Tuesday.

The utilities have projected that the peak demand this summer will hit about 10,860 megawatts.

The Valley has an electric system with a peak capacity of 11,390 megawatts -- only about a 4.8 margin over the predicted peak. However, the capacity is expected to jump to 12,100 megawatts in the first or second week of July when three new transformers are installed at the Westwing substation northwest of Phoenix. That would provide an 11.4percent margin of reserve, assuming the peak- demand forecast is accurate.

"That's a pretty hefty cushion," Hatch-Miller said. "Usually 7percent is considered adequate."

But he said it may not be adequate if wildfires force the shutdown of one or more high-voltage transmission lines feeding the Valley.

"We have plenty of power ... but I am concerned about the fire situation," he said. "People need to be careful. It's a tinderbox out there."

Although wildland fires usually don't damage power lines and towers, high-voltage lines often have to be shut down to ensure the safety of firefighters, he said.

APS spokesman Jim McDonald said the utility is sticking with its peak demand prediction of 10,860 megawatts this summer. Also, he said, the utility is confident the system has sufficient capacity to meet that demand without the need for conservation appeals.

"These are good questions to ask, but our forecast looks solid," he said. "And we have the resources we need."

He added that it's not surprising that a record for peak demand would be set this early in the summer. "This is Arizona. It gets hot, and we're growing," he said. "We set records (for electricity use) every year."

He also was reassuring about Yuma's situation, saying a new transformer will be installed today, adding 40 megawatts of capacity for that city.

SRP spokesman Scott Harelson said his utility also is in good shape this summer. He said SRP customers will benefit from the expansion of the San Tan power plant in Gilbert, which added 550 megawatts of generating capacity in April.

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