A secondary distribution box, also known as a sub-distribution panel, generally supplies power to a specific area. It is designed with inner and outer doors, features a sprayed plastic exterior for safety and appearance, and also has a rainproof top suitable for outdoor work. A feeder usually begins with a feeder breaker at the distribution substation. Many feeders leave substation in a concrete ducts and are routed to a nearby pole. A tertiary. Generally, the secondary distribution systems are designed in single phase for areas of residential customers and in three phase for areas of industrial or commercial customers with high-load densities. From the transformer's low-voltage side (0.