Mesh grounding to suppress potential differences between telecommunications equipment caused by direct lightning strikes

Abstract

When lightning hits a building, telecommunications equipment within the building is occasionally damaged due to induced voltage in the telecommunications cables, power-feeding cables, and grounding wires installed in the building. This induced voltage is caused by the lightning current flowing into the pillars and girders of the building. To suppress these induced voltages, mesh-wiring and branch-wiring grounding systems have been designed to protect connected devices from lightning. However, there have been few experimental reports and little quantitative analysis on the efficiency of these grounding systems. Therefore, we have studied the impedances of pillars and girders, and the lightning current distribution in a building, through experiments using an actual reinforced concrete building. In this article, based on our previous results concerning the lightning current distribution, we investigate the induced voltage in the grounding wires experimentally and theoretically. From the relationship between the current distribution in the pillars and girders, and the induced voltages in the grounding wires installed in the floor, we found that the induced voltages can be estimated by applying vector-potential methods to the current in the girders. By measuring the induced-voltage differences between a single-wiring, a branch-wiring, and a mesh-wiring grounding system, we also found that the mesh-wiring system provides the best protection for the telecommunications equipment and reduces the induced voltage between devices to one-fifth of that with the single-wiring or branch-wiring systems. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(3): 56–65, 1999