As much as 60 percent of Provo was without electricity for four hours Monday when power equipment failed in subzero temperatures, closing schools and area businesses.

The north half of the city was without electricity until 11 a.m, which closed public schools for the day and postponed classes at Brigham Young University. Many businesses did not open until power was restored.

Glen Spivey, city power distribution manager, said all substations were up by 11 a.m., even though the department still was getting a few calls from residents with power problems. He did not believe that those cases were related.

"We really don't know if the equipment was faulty or if it was from the extreme cold," he said. "We know the cold caused it, but we don't know if the equipment was faulty to begin with."

An outage earlier Monday covered a smaller areas. Electricity first went off at at 1 a.m. when guy wires broke on a power pole at Eighth North and Geneva Road. That outage affected the west part of city, from 16th West to Utah Lake.

Spivey said the line went down when three three-quarter-inch steel bolts that attach the guy wire to the pole broke in half. When the bolts broke, the guy wire fell and it brushed against some energized conductors and burned them.

The larger power outage occurred between 5 a.m. and 6 a.m. when a 44,000-volt switch at 1750 North and about 850 East broke in half. The switch consists of two large porcelain insulators attached to a mounting bracket. It sheared where the insulator attaches to the mounting bracket, Spivey said.

When the switch sheared, the conductor fell into some energized circuits below. The second outage was the worst of the two and included all of BYU campus and Provo from Ninth North to the mouth of Provo Canyon.

Failure of the 44,000-volt switch also caused the Gillespie Substation near the mouth of Provo Canyon to go down at about 6 a.m. That was one of 11 stations down during the outage.

The Provo City Power Plant also lost its power at about 6 a.m, shutting down the city's district heating supply, which is piped into Utah Valley Regional Medical Center and Provo School District's administrative offices. The plant was back in operation by 7:20 a.m.

Classes at Brigham Young University were postponed until 11 a.m.

BYU spokesman Paul Richards said the BYU weather station recorded temperatures at 20 degrees below zero Monday between 6 a.m. and 7 a.m. That temperature ties a record set exactly 40 years ago Monday.

Provo schools were canceled because of the outage. Superintendent Jim Bergera said Monday's closure was only the second closure that he knows of in the district's history.

Although not all schools in the district were affected by the outage, Bergera said the district canceled school because the central schools where lunches are made were without electricity.

Pleasant Grove also reported a minor power outage Monday morning because of the cold weather.

Alan Bezzant, region engineer for Utah Power & Light Co., said about a third of the city was without power for about 45 minutes after a guy wire broke and caused a pole to snap at approximately 6:45 a.m.