Michigan regulators will investigate power outages stemming from a pre-Christmas holiday ice storm that knocked out service to 660,000 customers.
The state Public Service Commission unanimously approved the probe at a meeting Wednesday.
Scores of tree branches broke and fell from the weight of ice during the storm.
Consumers Energy and DTE Energy are Michigan's largest utilities and say they restored power within a week of the storm that hit Dec. 21-22. Customers without electricity at least 120 hours could get a $25 credit.
Regulators say the sheer number of people without power prompted the investigation. They want to know how Consumers and DTE responded to the storm.
Other questions include whether the utilities properly maintained their systems before the storm and addressed downed lines in a timely manner.
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