Topological Grounding Anomalies

Two principal anomalies found in current grounding practices are discussed The ground conductor penetrating a shield, and a grounded but open shield. Good grounding practices are simple when viewed from the topological viewpoint. A system is divided into different zones, each separated from the other by an electromagnetically impervious barrier, and each zone has its own ground system. Because lightning is a broadband phenomenon, the separation of the zones must also be achieved over a broadband if a system is to be protected against the effects of lightning. It is well understood that aircraft avionics systems do not require a connection to earth to be protected against lightning. This is much less recognized for ground equipment and ground facilities. Here, the practice of connecting the signal reference ground to the earth electrode has serious consequences in the event of a lightning strike for the equipment connected to it, unless the ground rod has zero impedance. In the topological approach, such a connection is only permitted if the grounding conductor does not penetrate the barrier surfaces that separate the different zones of the system. Experimental data to support this approach are discussed.