Traditional power system analysis assumes linear loads from resistance and electromagnetic devices. Many loads are nonlinear because of electronic switching power supplies used in computers, variable frequency ac drives, and uninterruptible power devices. The power system design and analysis for these systems is considerably more complex. Traditional definitions and terms must be redefined for the nonlinear systems. The meters and sensors require a different design. The addition of harmonic currents demands that the wiring and electromagnetic devices must be de-rated. The mathematics for analysis has more terms and is more tedious. The paper provides tools for resolving these problems.