Falling fuel prices will give Duke Energy’s customers in North Carolina a temporary reprieve from the rate hikes of early this year.

The N.C. Utilities Commission has approved rate adjustments that will cut typical customer bills by about $2.49 a month beginning Sept. 1. That will partly offset a $7 monthly increase that went into effect for residential customers in February.

The changes don’t affect customers of Progress Energy Carolinas, now a Duke subsidiary. It will affect some 1.8 million other Duke Energy customers in North Carolina, including about 170,000 customers in Durham, Chapel Hill and other parts of the western Triangle.

In South Carolina, Duke has asked for a decrease that would effectively wipe out the $6 monthly rate increase approved in January. It will go into effect Oct. 1 if the S.C. utilities commission approves.

But the rate drops are likely to be only a pause in an upswing of electric rates in both states. Duke and Progress plan to seek general rate hikes in both North and South Carolina later this year.

Duke’s increased reliance on natural gas to fuel its power plants, as well as falling gas prices, account for the falling rates.

Duke, which for years has relied on coal and nuclear power, used 43 percent more natural gas in 2011 than in 2010, it told North Carolina regulators. Gas prices fell 6 percent.

Natural gas is flooding energy markets as the controversial drilling technique called hydraulic fracturing, or fracking, taps deposits in the Northeast and Southwest.

Rates in both states are adjusted each year to reflect changing fuel costs, which utilities pass to customers without markups.

The North Carolina adjustments approved Thursday equalize Duke’s actual fuel expenses with projected costs for 2011, when the company spent less than expected. They also include Duke’s cost of complying with a 2007 renewable-energy law.

Henderson: 704-358-5051 Twitter: @bhender