Asymmetries of earthing arrangements and equipotential bonding systems in buildings and the effects on EMC

Abstract

Asymmetric building structures force to build the earthing arrangements, the armouring of the building and the equipotential bonding system to be asymmetric as well. Another reason of asymmetries in earthing and equipotential bonding arrangements in symmetric building structures is the unawareness of planners and construction workers. As a consequence the building's electromagnetic compatibility (EMC) characteristic is influenced negatively and problems (such as interferences, failures or errors) when using sensitive electronic devices can occur. Both the ohmic and the inductive interference can be recognized as stray-currents in the PEN and PE conductors as well as in the earthing arrangement and the equipotential bonding system. As these currents are concentrated in the asymmetric zones, borderlines of buildings (armouring) and the PE/PEN/EB system they cause there relevant electromagnetic fields. The coupling of currents into the building installation can be caused by the external fields of high-voltage or railway facilities, by the fields of current-carrying low-voltage cables inside the building, by the asymmetric load of facilities (back current over PEN and EB conductors and building armouring). If the building structure is symmetric, both the currents and the fields extinguish in the ideal case or at least can be held low. In the contrary, the case of having an asymmetric building structure the external electromagnetic fields or the stray-currents can be amplified. The task of the EMC is to protect facilities against electromagnetic fields according to the limits which are specified in the actual standards. Since the fields in buildings are generally low, in this article low-frequency interfering fields are dealt with, which can interfere with sensitive equipment (i.e. in a hospital). Electromagnetic fields in the low-frequency range are the aim of the article (16.7 Hz or 50 Hz).