Techniques of effective cellular site facility protection

One of the most challenging electrical protection environments is the cellular/PCS (personal communications system) antenna site. Many failure instances were examined and risk factors have been determined. The results show that typical electrical protection at the network interface does not address certain scenarios likely to occur at cellular tower sites. This article discusses why copper telephone cable and premises equipment are vulnerable to lightning-related events. The National Electric Code (NEC) does not address these lightning-related issues. Some lightning-mitigation techniques used at telephone central offices, which have been addressed previously by BELLCORE, including the concept of isolated ground planes, are discussed as they apply to cell/PCS sites. This article discusses one protection scheme (isolation) for typical telephone facilities into cellular antenna sites and the associated buildings or equipment housing. Also discussed are less specific techniques such as minimizing the ground impedance, eliminating or diverting circulating currents, and special coaxial protection. Ground potential rise (GPR) and electromagnetic induction (EMI) occur at the same time during unbalanced power line faults. The experimental part of the research examines whether isolation at the network interface at cell sites can address GPR and longitudinal induction due to lightning.