Abstract: This research paper focuses on or proposes a smart uninterruptible power supply system with a phase selector and automatic changeover to intelligently manage three distinct power sources, such as the grid, considered the main power supply, the generator, and solar, considered as backup supply systems, to ensure uninterruptible power to critical applications. The novelty of the proposed design lies in its incorporation of the grid, generator, and solar power sources, along with an automatic changeover switch and source selector, and its ability to avert power supply interruptions when any of the power sources is active or present.