Abstract: In respond to the requirements of national energy conservation and emission reduction policies, and to vigorously promote energy conservation efforts, and help achieve the goals of "carbon peak and carbon neutrality", power grid enterprises and users carry out the replacement of high energy consumption transformers with energy efficiency levels of S9 and S11, including poles-mounted transformers, European and American box-type distribution station transformers and old transformers in distribution rooms. The construction and maintenance personnel mainly employ the mobile box transformer bypass operation method to replace transformers without causing power outage. Due to the limitations of the operating environment and other factors, there is no suitable temporary grounding device outdoors. Therefore, the neutral point of the low-voltage side of the mobile box-type transformer and the grounding of the shell protection are often installed at the neutral point grounding device of the distribution transformer. This paper presents a theoretical analysis and simulation study of voltage transfer and electric shock risks caused by line faults on both the high- and low-voltage sides sharing the grounding device in the above scenario. Furthermore, measures are proposed to mitigate the risk of electric shock during operation.