Hawaiian Electric Co.'s customers on O'ahu will see their average monthly electric bill increase by $6.48 under a rate hike approved by the state Public Utilities Commission.

The PUC approved an interim 4.7 percent rate hike for HECO's 294,000 customers, and that will raise company revenues by $61.1 million.

The effective date for the increase has not yet been set.

"For a small business, it's frustrating," said Elmer Guzman, owner of the Poke Stop in Waipahu. "It's hard when our costs are always rising."

HECO said the rate hike is necessary to pay for more than $200 million in new capital investment projects.

"We know how difficult a rate increase is in this economy, but it is our responsibility to meet the energy needs of our customers," said Robbie Alm, HECO executive vice president.

The typical residential household using 600 kilowatt-hours a month will see its monthly bill go from $122.58 to $129.06, HECO said.

The electric company is seeking an additional 2 percent rate increase, which would raise HECO's annual revenues by another $25.7 million.

That request is still under review by the PUC. The PUC said it will issue a final order on the 4.7 percent interim rate hike and the outstanding 2 percent request at a later date.

According to HECO, the rate increase will pay for a number of projects that have been completed in the past two years, including: