PORTLAND — The parent company of Central Maine Power is selling three natural gas utilities in New England to help pay for a $1.4 billion power grid upgrade in Maine.

Utility company UIL Holdings said today that it will buy Southern Connecticut Gas Co., Connecticut Natural Gas Corp. and the Berkshire Gas Co. of Massachusetts from Iberdrola USA for $885 million.

Iberdrola USA, a subsidiary of the Spanish energy company, says the deal will help fund power grid improvements in Maine, where CMP plans to double the capacity of the grid with a new 345,000-volt transmission line from Orrington to Eliot.

Iberdrola will fund the improvements, about half with cash, and half through borrowing. The money will be recouped from New England ratepayers.

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