Nowadays, the installation of photovoltaic(PV) systems integrated into structures has increased. Suitable PV systems are difficult to install with an optimal installation angle due to shape and aesthetics of architecture. This is caused by string mismatch depending on incident irradiance. Also, it is reduced the generated power of a PV system. To compensate the generated power of a PV system, a module-level power electronics(MLPEs) such as power optimizer and micro inverter is applied. Also, in some countries, building integrated photovoltaic(BIPV) systems must include a rapid shutdown function using MLPEs for safety. The MLPEs have been studied for improving the generated power. However, research on fault analysis of PV system with the MLPEs is insufficient. In this paper, short circuit fault and ground fault of a PV system are analyzed through the experimental results. A test bed is configurated with 16 series and 3 parallel and each of module is connected with a power optimizer. The short circuit fault is developed between connection of a string. When the string short circuit fault occurred, a reverse current over 500A is confirmed depending on power grid, and the module voltage is regulated to 1V. When the ground fault occurred at positive poles, the string input voltage is reduced to 16V. However, when it occurred at negative poles, the voltage is confirmed higher than inverter input voltage. As a result, at the post-accident, an optimizer is expected to be work for safety to firefighter, engineer and so on. On the other hand, it is confirmed that the accident can affect the optimizer at the time of the accident. Therefore, the PV system has to keep using protection device even using optimizer for safety.