Earth? What earth?

Abstract

The word `earth' or `ground' means many different things to many electrical engineers. In an electrical installation these words can be used to mean either the protective conductor in a mains cord; the common bonding network of the building; the earth mass electrodes of the lightning protection system, or the conductor of the mains supply that is connected to an earth mass electrode at the distribution transformer. This paper describes the relevance of connections from an electronic equipment to a protective conductor, common bonding network, or earth mass, for a number of electromagnetic (EM) phenomena. A knowledge of where the currents associated with EM phenomena actually flow is needed for a proper bonding and earthing design for the control of (EM) phenomena. The outcome of such an analysis shows that some EM phenomena are strongly affected by such connections, while some are not. Safety issues are not covered here, except to say that safety should never be compromised for the sake of EMC. So even when EMC is improved by removing a protective conductor (for example, to reduce the amount of hum in an instrumentation or audio system, which is still a common practice) this should never be done if it might contravene safety requirements. (8 pages)