The paper puts forward a recent practical issue which has never been addressed before that is associated with resonant grounded networks fed from multiple independent transformers and located in the same substation. This situation is common when the network is not initially designed as a resonant grounding network and the intention of using resonant grounding scheme is to reduce the risk of bushfire due to ground faults. In these situations, undesirable over-voltages are noticed on several practical healthy networks when faults occur on other networks. The paper analyses this phenomenon and investigates the factors impacting these unexpected over-voltages to help industries associated with such phenomenon to achieve the best strategies to avoid it.