When choosing a power supply that's right for you, the primary selection criteria are the input voltage, the output voltage, and the output power capacity. Your typical input voltage choices will be either 120–240 V single-phase (the most common), or 230–480 V three-phase. Designing an electrical power distribution system is a crucial process that ensures the safe and efficient delivery of electricity to homes. Primary distribution systems consist of feeders that deliver power from distribution substations to distribution transformers. Many feeders leave substation in a concrete ducts and are routed to a nearby pole. From homes, offices, and industries to dangerous locations, these boxes help prevent electrical overloading and failures.