Design And Construction of an Automatic Phase Selector

Reliable supply to single-phase loads remains a practical challenge in many residential, commercial and light-industrial settings where three utility phases are available but individual phases are frequently affected by undervoltage, interruption or imbalance. Manual phase changeover is still widely used in such contexts, yet it exposes users to avoidable downtime, switching delay, contact wear and safety risks. This study presents a low-cost automatic phase selector that senses three input phases, ranks the available phases according to programmed priority and voltage availability, and connects the load to the best available line through a relay/TIP41 switching stage. The implemented system used an ATmega328P-PU microcontroller, three voltage-sensing channels, transformer-isolated low-voltage inputs, rectification and 7805 regulation, relay switching, transistor drivers, a 16 x 2 LCD display, and a printed circuit board. The prototype was designed, simulated in Proteus, assembled on a PCB and tested under three operational scenarios: normal operation with phase one active, phase-one interruption with transfer to phase two, and phase-one/phase-two interruption with transfer to phase three. The results showed that the device detected the active phase, displayed phase status, and changed over from a failed line to the next available line without requiring manual intervention. Cost analysis indicated a prototype bill of materials of GH₵ 459.50, equivalent to USD 30.37 at the reported exchange rate. The study therefore demonstrates that a microcontroller-centred phase selector can provide a simple, affordable and locally buildable approach to improving continuity of supply for low-power single-phase loads. Its contribution lies not in replacing certified industrial automatic transfer switches, but in showing how embedded control, structured sensing and low-cost switching can be integrated into a compact prototype for educational, domestic and small-workshop applications. Future versions should improve isolation, incorporate calibrated RMS measurement, add overvoltage and undervoltage thresholds, introduce generator or inverter priority, and include remote fault notification through GSM, SMS or Internet-of-Things modules.