Under voltages and over voltages are caused by faults on power lines, and the subsequent actions of fault clearing devices. Also, by heavy loads, such as machinery start-up and by the slow reaction of power company regulating equipment. Since computer equipment is designed to operate close to nominal voltages, the effects of these voltage variations can cause serious problems. Voltages can drop as much as 20% of nominal. This can result in expensive and time consuming errors, loss of information, downtime, recovery and rerun costs and possible equipment damage.