What type of underground electric system has a single source of feed?

The radial underground electric system is characterized by having a single source of feed. In this configuration, electricity flows from the power source through a series of lines to the loads, with each customer or circuit served directly from this main source. The system is designed so that if the main feeder fails, the sections of the system downstream from that point also lose power, which can be a drawback in terms of reliability.

In contrast, other types of systems operate differently. A looped system has multiple feed points, creating a closed loop that allows electricity to take alternative paths if one section fails, enhancing reliability. A network system is more complex, involving multiple sources and interconnected pathways that allow for redundancy and load balancing. Duplicate systems provide an additional layer of reliability by having parallel paths for the electricity, ensuring that if one path fails, the other can continue to supply power.

Thus, the radial system's straightforward design, with its single feed point, clearly distinguishes it from these other configurations, confirming it as the correct choice.