Duke Energy is asking its customers in North Carolina and South Carolina to reduce electricity usage during the next 24 hours to help avoid potentially high energy demand caused by the extreme cold. A statement from the Charlotte-based utility says the most critical time to reduce usage is Thursday between 5 a.m. and 10 a.m. Vice President of Transmission System Operations Nelson Peeler says if it becomes necessary, Duke Energy will institute rotating or sustained outages across its grid.