ABSTRACT
Electrical surge arresters (ESAs) must be metal oxide varistors (MOVs) or spark gaps. When a spark gap is specified, the ESA must be enclosed within a metal case. Discharges must be contained within the case; no external corona or arcing is permitted. ESAs must be factory installed with minimum lead lengths within the outer compartment. For all power filter/ESA assemblies, the ESAs must be installed a minimum of 75 mm (3 in.) apart, with terminals at least 75 mm (3 in.) from a grounded surface. For telephone filter/ESA assemblies, the ESAs must have a minimum clearance spacing of 25 mm (1 in.), and terminals must be at least 75 mm (3 in.) from a grounded surface. Each phase, neutral, and telephone circuit conductor must be connected through an ESA to the ground bus.
