AUGUSTA – Utility regulators said Friday they have ordered Central Maine Power to refund some $2.75 million in overcharges to more than 13,400 customers who had power lines extended to their homes or businesses after July 1, 2000.

The Public Utilities Commission said CMP billings for new line construction had erroneously included a “profit adder” charge that amounted to 5 percent of total costs for the line from 1999 to February 2004 and was later increased to 10 percent.

Customers must pay the direct costs of line extensions, along with an additional 16 to 21 percent of those amounts to offset indirect administrative and support expenditures.

“The PUC determined that the extra ‘profit adder’ charge was not approved by the commission and the funds collected for the past six years should be refunded,” the PUC said.

The charge came under scrutiny after Peter Marion of Baldwin contacted the PUC’s Consumer Assistance Division with concerns about the amount CMP charged him to extend a power line to his new home.

A call to CMP was not immediately returned.

Most of the 13,000 residential customers and 400 businesses affected by the PUC order should receive a refund by Dec. 1, the commission said.

“This case serves as an excellent reminder that the PUC has resources available to utility customers to help them when they are dealing with a problem,” Kurt Adams, the commission chairman, said.