"I don't think (Monday) says anything one way or the other about the coming summer months," said Gregg Fishman, a spokesman for the California Independent System Operator, an agency that manages most of the state power grid.

A net increase of up to 9,000 megawatts of power has come online in California since the power crisis that caused rolling blackouts and surging electricity bills in 2000-01, Fishman said. One megawatt powers 750 to 1,000 homes. More than 18 power plants have been built or completed since 2000, most able to produce 50 megawatts.

"But we haven't seen the transmission grid keep up with that capacity," he added.

That means there could be "choke points" in the transmission of power this summer, something that could cause a blackout just like on Monday.

When power use surged on Monday because of record high temperatures, one key transmission line that brought electricity into the region overloaded and had to be shut down, Fishman said.

This affected residents in area cities Arcadia, Covina, El Monte, Temple City, Monrovia, Whittier and others for about 20 minutes Monday evening.

Officials say during the summer months they expect major strains on power systems but will not be caught off guard.

"It was certainly unexpected," said Steve Conroy, spokesman for Southern California Edison, serving the San Gabriel Valley customers who lost power Monday.

Conroy said this is a time when customers should begin taking steps to lower their reliance on electricity during the summer.

The No. 1 demand is air conditioning, but steps can be taken to cool your home without using so much juice, Conroy said.

Edison features tips for residents wanting to make their dwellings more energy efficient on its Web site, www.sce.com.