In energy conversion studies, some situations have been aimed at up to now. According to this, while the direct voltage is converted from some renewable energy sources to the alternating voltage, the shape of the voltage must be close to the sinus. Therefore, the works are being done on inverters with multi-levels. As the level of the inverters increases, the number of switches and control signals on them increases and it becomes harder to find the possible errors. Finding faults of a device with a large number of transistors with control signals is important, very difficult, and time-consuming task. This paper addresses the issue of determining fault conditions for a multi-level inverter with a very complex switching scheme. The results are analyzed and evaluated after the values obtained in the simulation are validated by the experimental study. For different switch fault conditions at the applications, the harmonic distortion of the alternating voltage is measured and made into tables. After that, different fault conditions of the 21-level inverter structure are explained when fault curves are created from the distortion value of the fault signals.