The double-digit percentage increase in the “standard offer” electric rates for medium and large business customers of Bangor Hydro-Electric Co. and Central Maine Power approved this week might not be as difficult to swallow as it sounds, a Bangor Hydro spokeswoman said Wednesday.

The medium business customers of CMP that rely on the standard offer will see a rate increase of 23 percent starting Sept. 1, while large business customers will see an increase of 32 percent. Bangor Hydro’ s medium business customers will see a rate increase of 21 percent and large business customers will have an increase just under 20 percent.

Yet those increases, Bangor-Hydro spokeswoman Susan E. Faloon said, affect on average only about 13 percent of the total bill that the 1,000 or so businesses pay monthly.

“We bill for that but that money doesn’ t go to us. We are just responsible for the delivery. There is absolutely no change to the delivery portion of the bill,” Faloon said Wednesday. “They will not see a 20 percent increase in their whole bill. It’ s just a supply portion of the bill.

“That ends up being about 13 percent of the whole bill on average,” she added. “For the businesses, the kilowatt-hour charges increase only about 2 cents per kilowatt hour on average. That’ s how it affects our customers.”

The Maine Public Utilities Commission on Tuesday approved the double-digit increase in the “standard offer” rates for medium and large business customers to help offset increasing natural gas and oil costs, commissioners said.

Residential and small commercial customers served by both utilities will not see an increase in their standard offer rates until February 2009. The PUC will seek bids for that power later this year.

At Bangor Hydro, small-class customers are defined as those whose peak demand is up to 25 kilowatts. Medium-class customers have peak usage of between 25 and 500 kilowatts, and any businesses that use more are called large-class.

Faloon estimated that about 60 percent of the 1,700 medium-class customers, plus three or four large-class customers, would be affected by the rate increase.

A CMP spokeswoman declined to comment on the increase, saying it was a PUC matter.