Simple Spot-Network Distribution System. The simple spot-network
distribution system (see Figure 13) should be used for installations that
have heavy loads concentrated in small areas and considerable distances
between such loads. This system has the inherent advantages of any network
system. The system is limited, however, because it is not provided with
secondary loops (refer to para. 220.127.116.11 for additional information).
Primary Selective Network Distribution System. The primary
selective distribution system (see Figure 14) should be used for industrial
applications in which heavy loads are evenly distributed. Each of the
selective network distribution system provides continuity of service in the
event of one primary feeder or transformer failure.
Primary Selective Spot-Network Distribution System. The primary
selective spot-network distribution system (see Figure 15) provides the most
reliable form of electric power distribution. In the event of a primary
feeder failure, the transformers connected to the unfaulted primary feeder
can carry all the load for the short period of time that it takes to transfer
the other transformers to the unfaulted feeder. Each transformer need not
have the total capacity of the load center.