Blackout/Power failure

Blackout/Power failure

Complete loss of power. Some literature considers a voltage drop below about 80V to be a blackout as well since most equipment will not operate below these levels.

Sag or Brownout

Sag or Brownout

Decrease in voltage levels which can last for periods ranging from fractions of a second to hours. It could be caused by heavy equipment coming on line such as shop tools, elevators, compressors etc. Also occurs when utility companies deliberately do this to cope with peak load times.

Spike

Spike

A tremendous increase in voltage over a very short period of time often caused by a direct lightning strike on a power line or when power returns after a blackout.

Surge

Surge

A substantial increase in voltage lasting a small fraction of a second, often caused when high powered appliances such as air conditioners are switched off.

Inrush current

Inrush current

The current drawn by any electrical device when power is initially applied. Computer equipment typically draws an inrush current of three to ten times the nominal operating value.