L.M. Kennedy, Joslyn Electronic Systems Division
Experience has established that AC and/or DC powered electrical/electronic equipment is particularly vulnerable to damage from lightning, switching surges and other overvoltage disturbances originating on power distribution facilities! Some types of electromechanical devices are also susceptible to damage from excessive transient voltages from these sources. Overvoltages are also generated within a load complex by switching of equipment, but their magnitudes are generally lower than surges from primary distribution circuits. The application of arresters that are specifically designed for limiting surge voltages on utilization circuits has proven to be an effective means of preventing equipment damage from these common sources of exposure. Overvoltage surges such as discussed above are inherent in the operation of a power distribution network and cannot be prevented. Providing adequate protection to insure service continuity and minimize maintenance expense must be assumed by the user. AC and/or DC powered equipment is usually designed to withstand "normal" overvoltage conditions such as limited voltage variation and the surges normally experienced when energizing equipment units. This is an economical practice because protection against abnormal over-voltages can be provided for an entire installation by the application of a properly selected and installed power arrester and/or signal protector. The following sections discuss the electrical and physical properties to be taken into consideration with regard to the nature of the problem (equipment protection), proper selection of an arrester for the defined problem and installation instructions.