Noise often originates in electrical motors and motor control devices, electric arc furnaces, electric welders, relays, and remote atmospheric discharges such as lightning. Although less destructive than a large rapid transient, electrical noise can cause computers to malfunction and can interfere with the operation of communications equipment or other sensitive electronic equipment. Voltage Sags A voltage sag is a short duration decrease in voltage values. Voltage sags longer than two minutes are classified as undervoltages. Sags can cause computers and other sensitive equipment to malfunction or simply shut off.
Undervoltage conditions can damage certain types of electrical equipment.
Interruptions Interruptions occur when voltage levels drop to zero. Interruptions are classified as momentary, temporary, or long-term. Momentary interruptions occur when service is interrupted, but then is automatically restored in less than two seconds. Temporary interruptions occur when service is interrupted for more than two seconds, but is automatically restored in less than 2 minutes. Long-term interruptions last longer than two minutes and may require field work to restore service.