The utility, however, backed off a request that people turn off holiday lights after taking criticism for spreading bad cheer.
"We want to be in tune with the festive nature of the season," said David Eskelsen, a spokesman for Portland, Ore.-based PacifiCorp, which serves parts of six Western states.
Now the company is asking people to delay turning on holiday lights until after 7 p.m. at night rather than keep the lights off.
Demand for electricity peaked again on PacifiCorp's system when temperatures dipped to the single digits December 10, Eskelsen said.
There have been no reports of widespread outages, but cold temperatures are expected to persist for a while, straining a Western power grid that stretches from northern Mexico to a piece of British Columbia, he said.
Most people heat with natural gas or another fuel, but Eskelsen said heating systems commonly use a blower, which contributes significantly to power demands.
Electric clothes dryers also are big electric users, and PacifiCorp was asking customers to wait until late at night to use them.
Customers also were asked to minimize the use of lights, computers, televisions and other appliances. The utility even asked people to cook with microwaves instead of regular electric ovens.
"We asking people to do easy and simple things," Eskelsen said.
PacifiCorp's Utah division, Rocky Mountain Power, went as far as to make a round of automated phone calls asking customers to cut back on power usage.
Eskelsen said all parts of PacifiCorp's system were under strain trying to deliver about 12,000 megawatts of power. The utility operates in Oregon, Washington, Idaho, Wyoming, Utah and a piece of northern California.
The last time Rocky Mountain Power asked customers to ditch holiday lights was 2000-01, when the utility sent an appeal to the Mormon church, which lights up Temple Square in downtown Salt Lake City.
That holiday season was complicated by California's experiment with deregulated power, which let energy traders game the system and shut down supplies of electricity to drive up prices, Eskelsen said.