South Carolina Electric & Gas Co. wants to raise electric rates an overall 2.99 percent to help pay for new nuclear units being built north of Columbia.

The Cayce-based utility, part of SCANA Corp., filed for the increase Friday with the S.C. Public Service Commission and the state Office of Regulatory Staff.

The $70 million-a-year request is part of a 10-year series of price hikes expected annually through 2018 to offset the $10 billion costs of building two units at V.C. Summer Nuclear Station in Fairfield County.

The new units will come online in 2017 and 2018. SCE&G jointly owns the nuclear power plant with state-owned utility Santee Cooper of Moncks Corner.

Paying financing costs while construction is ongoing, as opposed to waiting until the project has been completed, lowers the cost of the new units by about $1 billion, according to SCE&G.

The investor-owned utility estimates the pay-as-you-build plan will save customers about $4 billion in electric rates over the life of the new units.

If approved, the monthly bill for a residential customer would rise 3.09 percent, or $4.34, for every 1,000 kilowatts of power used, to $146.63. That's almost $52 a year.

Commercial and industrial customers would also see their bills go up.

The rate hike would take effect in October if approved. SCE&G serves about 673,000 electric customers across South Carolina. About half are in the Charleston area.

Rates for SCE&G customers have jumped 13 times over the past six years. Six of those were connected to the nuclear units. The others were general rate hikes.

Reach Warren L. Wise at 937-5524 or twitter.com/warrenlancewise.