The emergency electric generator was supported with several mount module to isolate any transfer of excitations from a combustion engine to a basement floor of responsible building. But the current mount module can not tackle the external excitations from a basement floor into the power plant so that it may fall into a unstable situation when earthquake events are occurred. One of countermeasures for the earthquake is to install a stopper structure against the rollover of the electric generator at a mount location. The stopper was designed as ‘L-shape’ structure to support the tilting movement and the dynamics of the stopper was not considered in the early stage of development process. In this paper, the dynamics of the stopper was considered by the measured response acceleration response of the basement floor during 100% electrical loading and the contribution of the stopper was analyzed from the spectral results. In addition, the feasibility of the modfied design of the stopper was tested under the same test mode.