Alternating current (ac) power generators produce sinusoidal voltage waveforms. Transmission through powerlines and transformers has little effect on the shape of the voltage. Electronic loads, however, produce distortions in the waveform. The amount of voltage distortion is a function of the amount of current and the impedance of the delivery system. Electronic equipment generally controls the current drawn by starting or stopping the current flow within each voltage cycle. The result is a nonlinear current draw and a distorted current flow. Thus, the introduction of modern electronic systems has required changes in the designs of private and utility electric power systems. Commercial buildings and industrial facilities are likely to contain equipment that distorts the voltage of the electricity supply. Modern designers try to restrict that effect to the smallest possible portion of the system.