Rocky Mountain Power is asking the Utah Public Service Commission to grant a rate increase of $66.9 million, effective early next year.

If approved, the hike would cost the average residential customer about an extra $2.70 per month, or about 4.5 percent on average, the company said.

"The proposed increases range between 4 to 6 percent for different customer classes," Rocky Mountain Power spokesman Jeff Hymas wrote in an e-mail to the Deseret News.

He added that residential customers would receive the lowest increases, based on the proposal.

"Because customer demand for electricity is growing, Rocky Mountain Power has been investing billions of dollars in new generating plants, transmission systems and distribution facilities," he said. "As these investments begin to provide service to customers, it's appropriate that their costs become part of customer rates."

Michele Beck, executive director of the Utah Office of Consumer Services, told the Deseret News that according to the utility's research, a 4.5 percent increase would be particularly unwarranted for homeowners.

"Their own study … doesn't justify giving that rate increase to the residential consumers," she said.

Beck said Rocky Mountain Power submitted information in its request indicating that residential electric customers should be subject to a 0.6 percent increase, much less than the 4.5 percent average being requested.

Under the proposal, the utility wants to raise its fixed monthly "customer charge" to $5.70 from the current level of $3. The charge is a regulated amount that each residential consumer is required to pay to cover expenses such as administrative costs and the costs of a meter and a power line to a home.

Beck said her agency is still in the process of reviewing the documentation for the request. Preliminary hearings on the proposal would likely take place this fall, with a decision possibly coming by December.

In April, the commission granted the utility a 3.34 percent hike. The utility had originally requested a $160 million rate increase in July 2008, but eventually agreed on the $45 million amount.

E-mail: jlee@desnews.com