When large restoration operations occur in cold weather, one of the issues our system faces during the re-energizing process is known as 'cold load'. Cold load is the amount of electricity customers demand as we try to re-energize areas that have been off for extended periods of time. In some cases, this results in greater demand than our system is designed to take all at one time, and shortly after the electricity is restored, circuit breakers automatically trip to protect the system from overload, and the power goes off again.
The main cause of this problem is the large number of electric heaters and furnaces coming on at the same time, which place an unusually heavy load on our system. We ask our customers to help by turning off the breaker switch to their furnaces in their homes if their power is out. All other breaker switches can be left on.
When the electricity is restored, customers should leave the furnace off for about 30 minutes so our system can 'settle out' after restoration, then turn on the furnace and gently bring the temperature of the building up to a comfortable level.