55-8 ET 200 Distributed I/O SystemEWA 4NEB 780 6000-02a5.1.4 Potential equalizationDifferences in potential can occur, for example, when different mainssupplies are used. Under these circumstances, potential differences mayoccur between the various parts of a system, if programmable controllers and inputs/outputs are connected bypotential-bonded couplings,or cable shields are connected at both ends and grounded to different parts ofa system.It is important to install potential equalization lines in order to minimizepotential differences and ensure the functionality of the electroniccomponents.Note the following points: The smaller the impedance of the potential equalization line, the higherthe efficiency of potential equalization. If shielded signal cables are installed between certain parts of the systemand connected at both ends to ground/protective conductors, it isimportant to ensure that the impedance of the additional potentialequalization line is not in excess of 10 % of the shield impedance. Select potential equalization lines having a cross-section adequate for themaximum equalization current.The following are empirical values for the cable cross-sections:– 16 mm 2 Cu for potential equalization lines up to 200 m in length– 25 mm2 Cu for potential equalization lines more than 200 m in length Use potential equalization conductors made of copper or galvanized steel. Use connectors with large contact areas to connect the potentialequalization conductors to the ground/protective conductor. Protect the potential equalization conductors against corrosion. Route the potential equalization conductors in such a way that the areasbounded by the potential conductor and the signal lines are as small aspossible.When do differ-ences in potentialoccur?Avoiding potentialdifferencesRules for potentialequalizationRouting cables; connecting and installing bus connectors
