LOS ANGELES - Wildfires near Los Angeles are close enough for Southern California Edison workers to keep a watchful eye on high-voltage powerlines, but through Friday morning only about 1,000 customers were without power, a spokesman for the utility said.

Several wildfires in Southern California by Friday morning were not affecting the major powerlines that make up the regional power grid, said Stephanie McCorkle of the California Independent System Operator, which manages the grid.

Southern California Edison spokesman Steve Conroy said workers were closely watching progress of several fires, and that one was about a mile from a transmission corridor for 220-kilovolt lines. On Friday morning, the fires were not advancing toward the lines, Conroy said.

Both the utility and the Cal ISO will continue to watch the advance of fires toward the major powerlines through the weekend, as a heat wave with triple-digit temperatures Fahrenheit is not to break until Sunday, forecasters say.

Southern California Edison is one of the largest utilities in the United States. It delivers power to about 4.9 million residential and business customers. SCE is a subsidiary of Edison International (EIX.N), and based in Rosemead in suburban Los Angeles.

The 1,000 SCE customer outages were caused by issues dealing with local distribution lines and local stations, and not equipment or lines on the high-voltage Cal ISO system.

All of this is happening on Friday, during the highest demand for electricity in 2009 in California.

McCorkle said the Cal ISO system, which transmits about 80 percent of the electricity used in California, expects demand of about 45,450 megawatts, which would top the high so far this summer of 43,637 MW on July 20.

A megawatt in Southern California can serve about 650 average households on average. That number of households served drops during high heat of summer as each customer boosts usage.

In Los Angeles, highs should reach about 102 degrees Fahrenheit (39 Celsius) on Friday, and higher than 110 F (43 C) in some parts of the San Bernardino Valley near Los Angeles.

There is enough reserve margin that unless powerlines are rendered inoperable unexpectedly by the fires, the system should hold, McCorkle and Conroy said.

Friday is the third day of a heat wave in California, causing more demand to power air conditioners helping residents and businesses battle the heat.

The record peak demand on the Cal ISO system of 50,270 MW was reached in July 2006, during a heat wave that led to more than 2 million customers losing electricity in the state. (Reporting by Bernie Woodall; Editing by Christian Wiessner)