Interruptions / Outages

The term outage is being used less and less. It's been largely replaced by the word interruption. The Emerald Book defines an interruption as, "The complete loss of voltage for a period of time." In order to help understand how long this "time period" is, adjectives like "momentary", "temporary", and "sustained" are used.

• Momentary implies a very short time frame, between a quarter-cycle and a few seconds and usually results from the switching of large blocks of loads.
  
• Temporary refers to a time frame of several seconds to a few minutes. These interruptions come from faults somewhere in the grid, but through switching and reclosure, operation voltage can be quickly restored.
  
• Sustained is a longer term time period. A sustained interruption may last indefinitely. Usually some form of manual intervention is required to restore power in this situation.