Systems and methods for detecting ground fault at the common DC bus in a high impedance ground system. A fault detection component can detect characteristics of an electrical signal including phase number (n) and fundamental frequency (H). A fast Fourier transform is performed at (n×H) and (2n×H), and the two values are compared. A healthy system (no ground fault) can display a large difference between (n×H) and (2n×H), while in an unhealthy system the difference can be minimal. A system and method of detecting variable phase number and fundamental frequency can be used in the calculation to perform the ground fault detection when these characteristics are variable.