July 25 (Bloomberg) -- California, the most populous state in the U.S., declared its second electricity emergency in two days as high temperatures drove demand for power.

The state called a stage 1 emergency, which is a public appeal for conservation, the California Independent System Operator said on its Web site. A stage 1 was declared yesterday and upgraded to stage 2, which allows utilities to curtail supplies to certain customers.

Utilities in other parts of the country have contended with blackouts caused by severe summer weather this month. About 600,000 customers were affected July 21 in the Midwest after heavy thunderstorms damaged equipment. A July 17 failure in New York City's Queens borough left 25,000 without power. Conservation and power curtailments helped avoid rolling blackouts yesterday in California, though equipment failures did cut electricity for thousands of people.

``We're happy that we got by yesterday, but please do not stop your conservation,'' Yakout Mansour, chief executive of the system operator, said at a briefing today. The system operator hopes to meet demand today without upgrading to stage 2, he said.

California utilities yesterday curtailed supplies of about 850 megawatts and conservation saved 1,400 megawatts more, Mansour said.

Demand today is expected to peak at about 50,157 megawatts, said the system operator, which manages most of the state's network. That would fall short of a record 50,270 megawatts set yesterday. One megawatt is enough for about 800 U.S. homes.

Heat Wave

Electricity consumption is surging amid a heat wave that has pushed temperatures to record levels in many cities. The high temperature in Fresno in the central part of the state is forecast to hit 112 degrees Fahrenheit (44 Celsius) today, matching a record set in 1931, the National Weather Service said.

Temperatures this afternoon reached 107 degrees in Concord, 96 in San Jose and 95 in Santa Rosa, the weather service said.

``These are clearly extreme weather conditions,'' Joe Desmond, undersecretary of energy affairs at the California Resources Agency, said at the briefing.

The state called its first stage 1 emergency of the year on July 22. Stage 1 may be called when the reserve margin, a measure of surplus power, falls to less than 7 percent. A stage 2 comes at less than 5 percent, and a stage 3, which would result in rolling blackouts, would be at less than 1.5 percent.

Electricity officials said power demand may ease as the weather cools later this week.

Cooler Weather

``Hopefully by Thursday and Friday, demand should be considerably lower and back into normal range,'' Gregg Fishman, a spokesman with the system operator, said in a telephone interview.

The high in Fresno is forecast to fall to 103 degrees by July 28, the weather service said.

``The system is weakening, but not as fast as we anticipated, so things will stay warmer than they would be for this time of year,'' Diana Henderson, a National Weather Service forecaster in Monterey, California, said in an interview.

Millions of people in California have suffered disruptions in electricity supplies because of damage to equipment caused by the heat and high level of demand.

At PG&E Corp.'s Pacific Gas & Electric, 1.1 million customers have lost power since July 21, spokesman Brian Swanson said. As of 2:40 p.m., about 26,000 remained without electricity.

``The challenge we are facing is the sheer number of different outage locations we need to get to,'' Swanson said. ``It requires a lot of manpower.''

In the Dark

About 20,000 customers without power are in 700 different clusters around the San Francisco area, Swanson said. Each customer represents a single home or business, so the number of people affected is higher.

Edison International's Southern California Edison has 9,300 customers without power. The company said yesterday that a total of 765,000 customers had supplies interrupted since July 13.

Utility crews from PacifiCorp, which serves states including Oregon and Washington, plan to help Southern California Edison to restore service, spokesman Tom Boyd said.

In the Midwest, Ameren Corp.'s utilities are still trying to restore power to about 142,000 customers in Missouri and Illinois, down from a July 17 peak of 600,000, spokesman Tim Fox said. Consolidated Edison Inc. has 208 customers without power from the Queens failure, spokesman Alfonso Quiroz said today.

Sempra Energy also owns a utility providing electricity in California.

To contact the reporter on this story: Greg Chang in San Francisco at gchang1@bloomberg.net

Last Updated: July 25, 2006 18:58 EDT