It may be intermittent or chronic. Noise introduces glitches and errors into executable programs and data files. Also known as brownouts, sags are short term decreases in voltage levels. Electric companies use sags to cope with extraordinary power demands. Hot summer days, when air conditioning requirements are at their peak, will often prompt rolling brownouts.
Sags also reduce the efficiency and life span of electrical equipment, particularly motors.
Also referred to as an impulse, a spike is an instantaneous, dramatic increase in voltage. Akin to the force of a tidal wave, a spike can enter electronic equipment through AC, network, serial or phone lines and damage or completely destroy components. Spikes are typically caused by a nearby lightning strike. Spikes can also occur when utility power comes back on line after having been knocked out in a storm or as the result of a car accident. Spikes cause catastrophic damage to hardware and loss of data.