Earth fault current distribution and proof method of global earthing systems

In order to estimate the currents as well as the relevant voltage drops in case of an earth fault, a calculation model was prepared to give an overview of possible dangerous earth potential rises, touch and step voltages. The combination of two inductively coupled loops and a low voltage model for an earth fault in a cable ring structure, which is made up from one single feeder operated with an open circuit breaker led to the calculation of the reduction factor. When inserting typical values for an urban low voltage network, it is shown that the earth fault current returns mainly through the cable sheaths and not via the grounding system of the afflicted ring main unit.