Radial, Loop, & Network Systems

There are three basic types of distribution system designs: Radial, Loop, or Network.

Radial System Graphic As you might expect, you can use combinations of these three systems, and this is frequently done. The Radial distribution system is the cheapest to build, and is widely used in sparsely populated areas. A radial system has only one power source for a group of customers. A power failure, short-circuit, or a downed power line would interrupt power in the entire line which must be fixed before power can be restored.

Loop System GraphicA loop system, as the name implies, loops through the service area and returns to the original point. The loop is usually tied into an alternate power source. By placing switches in strategic locations, the utility can supply power to the customer from either direction.

If one source of power fails, switches are thrown (automatically or manually), and power can be fed to customers from the other source.

The loop system provides better continuity of service than the radial system, with only short interruptions for switching. In the event of power failures due to faults on the line, the utility has only to find the fault and switch around it to restore service. The fault itself can then be repaired with a minimum of customer interruptions.

The loop system is more expensive than the radial because more switches and conductors are required, but the resultant improved system reliability is often worth the price.

Network System GraphicNetwork systems are the most complicated and are interlocking loop systems. A given customer can be supplied from two, three, four, or more different power supplies. Obviously, the big advantage of such a system is added reliability. However, it is also the most expensive. For this reason it is usually used only in congested, high load density municipal or downtown areas.