A state watchdog for power prices has issued a warning to customers of electricity supplier North American Power, which charges variable rates for electricity after the conclusion of a six-month fixed contract.

The Maine Office of the Public Advocate said thousands of Emera Maine and Central Maine Power customers signed up earlier this year for six-month contracts with North American Power that are now set to expire.

“When the fixed rate term expires, customers are automatically rolled over to a variable rate, where the price changes each month based on wholesale market prices,” the consumer warning from Public Advocate Tim Schneider said, noting that power prices are expected to spike again this winter. “Last winter, some variable rates went as high as 25 cents per kilowatt-hour, or nearly four times the standard offer price, costing some customers hundreds of dollars in excess costs.”

Schneider wrote that customers of North American Power are supposed to receive notices of the change to variable pricing, but some customers haven’t been notified of the switch back to variable rates.

“North American Power is supposed to let customers know their contract is expiring, but we know some customers haven’t gotten notice, and we’re concerned that those who have received notice may not understand the potential costs of switching to a variable rate,” Schneider said in the statement.

He recommended customers ask North American Power when their contracts expire by calling 888-313-9086 or emailing customercare@NAPower.com.

For customers already on variable rate plans that could expose them to spikes in price this winter, he suggested a switch to the standard offer price negotiated each year by the Maine Public Utilities Commission or exploration of other options for competitive electricity providers.

Darren is a Portland-based reporter for the Bangor Daily News writing about the Maine economy and business. He's interested in putting economic data in context and finding the stories behind the numbers.