Reverse Operation of Surge Protective Devices on RS 485 Communication Lines Under Lightning Ground Potential Rise

In protecting against lightning damage, specifically related to RS 485 industrial communication systems, the approach is typically to apply surge protective devices as mitigation measure. However, knowledge about the RS485 communication system dictates that a single point earth is required for its successful operation. Reverse operation of surge protective devices, applied downstream from the data acquisition unit, are likely to override the single point earthing system to introduce a multipoint earthing system, that can lead to exacerbated damage in large industrial plant, compared to before the installation of the surge protective devices. In this paper, the behaviour of a surge protective device applied to a typical industrial communication line, is assessed with support of numerical modelling to demonstrate the anticipated reverse operation of the protective device. This paper raises awareness about lightning ground potential rise and the application of surge protective devices, particularly in the case of wire-line technology, important to the lightning protection system designer.