Variations and discontinuities in the AC power supplied by an electric utility can cause severe performance problems with sensitive electronic equipment. If AC line disturbances reflect through the DC power supplies of equipment such as data processing computers, telecommunications switching centers, or complex process control systems, the result is frequently erratic operation, unscheduled shutdown, or even component failure. Utilities make every effort to deliver clean well-regulated AC power to their customers, but the extent to which they are successful is often beyond utility control. Breaker tripping and reclosure for fault clearance, random switching of heavy loads, lightning strikes, noisy motor controllers, and an endless number of similar occurrences can and will introduce AC line disturbances about which the utility can do little. From a practical point of view, therefore, the user of sensitive electronic equipment should not be surprised if this equipment is exposed to "dirty" power, which, if not cleaned up, can cause equipment problems.
